A DISSERTATION ON “EVALUATION OF ANTERIOR SEGMENT IMAGING TECHNIQUES IN DIAGNOSIS OF KERATOCONUS” by Optom. Ankit Varshney

1. A DISSERTATION ON
“EVALUATION OF ANTERIOR SEGMENT IMAGING
TECHNIQUES IN DIAGNOSIS OF KERATOCONUS”
BY
ANKIT S. VARSHNEY
(2nd
YEAR, M. OPTOMETRY)
Under the guidance of
Dr. Priti Kapadia (M.S. Ophthal)
Dr. Mahendrasinh Chauhan (M.S. Ophthal, D.O.M.S.)
HARI JYOT COLLEGE OF OPTOMETRY,
ROTARY EYE INSTITUTE, NAVSARI.
2013- 2014.
Affiliated to
VEER NARMAD SOUTH GUJARAT UNIVERSITY, SURAT

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“EVALUATION OF ANTERIOR SEGMENT IMAGING
TECHNIQUES IN DIAGNOSIS OF KERATOCONUS”
A Dissertation SUBMITTED TO THE
VEER NARMAD SOUTH GUJARAT UNIVERSITY, SURAT.
In partial fulfilment of the regulations for the award of
THE DEGREE OF MASTER IN OPTOMETRY
BY
ANKIT S. VARSHNEY
(2nd
YEAR, M. OPTOMETRY)
Under the guidance of
Dr. Priti Kapadia (M.S. Ophthal)
Dr. Mahendrasinh Chauhan (M.S. Ophthal, D.O.M.S.)
HARI JYOT COLLEGE OF OPTOMETRY,
ROTARY EYE INSTITUTE, NAVSARI.
2013 - 2014.
Affiliated to
VEER NARMAD SOUTH GUJARAT UNIVERSITY,
SURAT

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ACKNOWLEDGEMENT
There are a number of people to whom I would like to express my heartfelt
gratitude for helping me with this thesis.
I am highly indebted to Dr. Priti Kapadia (M.S Ophthalmology) Professor
and Head in Dept. Of Ophthalmology, GMC, Surat.
Dr. Mahendrasinh Chauhan (M.S Ophthalmology, D.O.M.S.) Principal of
Shree Bharatimaiya College of Optometry, Surat and Mr. Nirav Mehta
(M.Optom) Rotary Eye Institute, Navsari without whose, constant support,
guidance and constructive criticism this study would not have been
possible.
I am very thankful to Mr. Sanjay Ahir and Mr. Abhinav for their guidance
and Statistic work during complication.
My hearted thanks to my dearest friend Keyur N. Sharma (M. Optom,
Fiacle, Fasco), Hima Patel (B.Optom), Disha Mistry (B.Optom) and the
staff of I Vue Laser Vision.
My whole hearted thanks to My Optometry student of Shree Bharatimaiya
college of Optometry, who helped me at some or other stage during this
study.
I am thankful to My Parents & Sisters.
Who have been constant sources of inspiration and support throughout my
academic career.
Last, but not the least I am thankful to all my patients who have co-
operated with me and without them, this study would not have been
possible. ANKIT S.VARSHNEY

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INDEX
1. INTRODUCTION………………………………………………………….. 5
2. AIM AND OBJECTIVES….………………………………………………..7
3. BASIC CONSIDERATIONS……………………………………………….8
4. REVIEW OF LITERATURE………………………………………………27
5. MATERIALS AND METHODS……………………………..…...……….31
6. OBSERVATIONS AND DISCUSSION….……………………………….34
7. SUMMARY …………..………………………………………………...…42
8. CONCLUSION……………………...…………………………….……….43
9. BIBLIOGRAPHY………………………………………………………….45

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1. INTRODUTION
Keratoconus is a bilateral, noninflammatory, progressive disorder characterized
by corneal ectasia, thinning and protrusion1. The disease induces myopia,
irregular astigmatism and has well defined slit lamp findings. The diagnosis of
more advanced keratoconus is not complicated, because of the typical
biomicroscopic and topographic findings, but the detection of subclinical or
forme fruste cases may impose difficulty3, 4
.
Currently the diagnosis of keratoconus is based on biomicroscopic findings,
corneal topography and ultrasound pachymetry. Placido-disk based corneal
topography only examines the anterior surface of the cornea and alteration in
the reference point or viewing angle may result in inaccuracy of curvature
measurement. Height data give a more accurate representation of the true shape
of the corneal surface because they are independent of axis, orientation and
position.
Corneal thickness is a valuable indicator of the health and physiology of the
cornea. Specifically, central corneal thickness (CCT) measurements are vitally
important for the diagnosis, treatment, and management of various ocular
conditions. For instance, Central corneal thickness is essential information in
situations where the cornea is thinned, either pathologically as in the case of
Keratoconus or intentionally via refractive surgery. In refractive surgery,
central corneal thickness is a crucial determinant of the amount of treatment that
needs to occur for the desired refractive outcome and also for the avoidance of
postoperative keratorefractive complications (Fakhry, Artola et al. 2002).
Ultrasound pachymetry requires the use of topical anaesthetic and contact with
the cornea. It is based on the reflection of sound from the anterior and posterior
corneal surfaces although the exact posterior corneal reflection point for
ultrasound waves is not known (Ehlers, Shah et al. 2008)18
.

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The Pentacam Comprehensive Eye Scanner uses a rotating Scheimpflug camera
and measures both anterior and posterior corneal surfaces by an elevation based
system. It allows the measurement of local elevation points by fitting the
corneal shape to a best fit sphere reference surface with variable diameters or to
an ellipsoid surface. Examination of the posterior corneal surface is important in
the early diagnosis of keratoconus as epithelial compensation can mask the
presence of an underlying cone on the anterior surface11
.
Elevation-based topography offers important advances over Placido-disc based
devices. The ability to image the posterior cornea and to produce an accurate
pachymetric map is itself significant. Elevation subtraction maps are also more
accurate in determining the cone morphology and in separating the false-
positive keratoconus suspect cases.
The goal of the present study is to compare central corneal thickness
measurements and corneal curvature from three instruments in corneas that have
been thinned due to keratoconus. Because each instrument is based on different
principles, measurements can biased when measured in abnormally thin corneas.
The purpose of our study was to diagnose the cases of Keratoconus with the help
of Pentacam, Corneal topography and Ultrasound pachymetry and to compare
the efficiency of these three methods for the diagnosis of Keratoconus.

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2. AIM AND OBJECTIVES
AIM:
The aim of this study was to diagnose the cases of Keratoconus with the help of
Pentacam, Corneal topography and Ultrasound pachymetry and to compare the
efficiency of these three methods for the diagnosis of Keratoconus.
OBJECTIVES:
1. To find the prevalence of keratoconus eyes at Lasik center.
2. To compare the results of Ultrasound Pachymeter (UP) and Oculus
Pentacam Scheimpflug system in measuring central corneal thickness
(CCT).
3. To compare the results of Oculus Pentacam Scheimpflug system and
Corneal topography (TMS-1) in measuring corneal curvature.

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3. BASIC CONSIDERATION
The cornea, a transparent tissue that covers the front of the eye, performs
approximately 2/3 of the optical refraction and focuses light towards the lens
and the retina. Thus, even slight variations in the shape of the cornea can
significantly diminish visual performance. It is reported though, that localized
loss of corneal thickness, and likely also degradation of corneal mechanical
properties, cause gradual tissue protrusion, which results in a more conical
appearance of the cornea that imposes blurred vision. Surgical interventions and
diseases of corneal tissue have been found to result in substantial changes in
corneal tissue structure, which can then also alter the biomechanical properties
of the cornea. The surgical procedures used to perform cornea l refractive
surgery result in changes in the corneal tissue structure, which affect the central
corneal thickness (CCT) and curvature of the cornea. Corneal refractive surgery
and corneal diseases thus can alter corneal biomechanics. Keratoconus is the
most frequently occurring disease of the cornea caused by a non -inflammatory
deterioration of the corneal structure 9.
Keratoconus, which was first described in detail in 1854 (derived from the
Greek terms kerato, meaning cornea, and konos meaning cone) is a bilateral,
non-inflammatory, asymmetric corneal degenerative disease that compromises
the structural integrity of the collagen matrix within the corneal stroma. 1 The
hallmark characteristic is the development of a localized, cone-shaped ectasia
(bulge or hernia) that is accompanied by thinning of the stroma in the area of
the cone. Corneal thinning normally occurs in the inferior-temporal as well as
the central cornea, although superior localizations have also been described.
This leads to increased irregular astigmatism as well as a steeper corneal
curvature causing myopia and has well defined slit lamp findings 3,
4. While the
spherocylindrical components of the refractive error can be corrected in the
patient’s refractive prescription, it is the residual irregular astigmatism that
cannot be easily corrected. This causes retinal image blur and poor visual
acuity. Keratoconus can cause mild to severe loss of vision. Even with advanced

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cases, patients do not “go blind” as there will always be the perception of light.
It typically presents in adolescence and progresses in a variable manner.
There are two types of Keratoconus: Posterior and Anterior.
Posterior Keratoconus is a rare condition in which the posterior corneal
surface has a conical protrusion into the anterior stroma which is a result of the
absence of stromal tissue. It is non-progressive and does not affect visual acuity
to any great extent.
Anterior Keratoconus, (hereafter, referred to as Keratoconus) or conical
cornea is a noninflammatory progressive ectatic and thinning disease process of
the cornea. The manifest behaviour of the disease is characterised by central
corneal stromal thinning, distorted corneal curvature, apical stromal scarring,
and anterior protrusion. These features impair vision due to the development of
irregular myopic astigmatism. Although most cases seen clinically are bilateral,
the disease is usually more severe in one eye than the other (Zadnik et al.,
2002). Unilateral cases have been reported, although the apparently unaffected
eye assumes a very mild keratoconic form. Kennedy et al. (1986) reported that
Keratoconus was bilateral in 59% and unilateral in 41% of cases. There are
many conflicting views and lines of evidence concerning whether or not
Keratoconus expresses any sex-linkage. While some authors believe that it
affects both sexes equally (Reardon and Lowther, 1973), Woodward (1984)
reported a greater prevalence among females in cases reported in the literature
before 1955. Still, others believe a male predominance (Karseras and Ruben,
1976; Korb et al. 1982; Lim and Vogt, 2002). The disease becomes manifest
around puberty in most cases, and the most common mean age of onset occurs at

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around age 16 (Krachmer et al. 1984; Ridley, 1956), although new cases have
been claimed to occur as early as two years (Bennett, 1986).
The progression is slow, taking up to five to six years to develop, thereafter
remaining stationary for many years. In others, there is rapid progression over
one or two years, followed by a long quiescent period (Duke-Elder, 1965).
It has well-described clinical signs, but early forms of the disease may go
undetected unless the anterior corneal topography is studied. The diagnosis of
more advanced keratoconus is not complicated, because of the typical
biomicroscopic and topographic findings, but the detection of subclinical or
forme fruste cases may impose difficulty. Early disease (Forme fruste
Keratoconus) is now best detected with Pentacam or elevation based
topography10, 11
. It is particularly important to detect the disease among
refractive surgery candidates, as keratorefractive procedures may worsen their
condition12
. Corneal protrusion causes high myopia and irregular astigmatism,
affecting visual quality.
FORME FRUSTE KERATOCONUS
Forme fruste Keratoconus, or subclinical Keratoconus, is an early form of
the disease that does not affect the patients best spectacle corrected visual
acuity, and does not present evidence of progression. Forme fruste Keratoconus
was first described by Amsler24
. It is essentially an extremely mild form of
Keratoconus that manifests as a central or para central zone of irregular
astigmatism.25
By definition, forme fruste of Keratoconus is characterized by
the lack of progression, having as a result the absence of diagnosis, if no special
examinations such as corneal topography are undertaken. Fo rme fruste of
Keratoconus is a contraindication for LASIK surgery and the diagnosis is very
important in refractive surgery candidates12
.

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3. 1. EPIDEMIOLOGY OF KERATOCONUS
An estimation of the frequency of Keratoconus varies widely depending upon
the source. Although the disease occurs in all races (Rabinowitz, 1998), there
appears to be a geographical influence on prevalence rate for the disease.
The incidence and prevalence of keratoconus in the general population has
been estimated to be between 5 and 23, and 5.4 per 10,000, respectively. A low
incidence of the disease is apparent in Japan, Taiwan, and Singapore (Khoo
1989; Chen et al., 2001), Mediterranean and Middle Eastern areas appear to
demonstrate high incidence and an increased manifestation (Totan et al., 2001;
Tabbara, 1999).
Differences on the rates reported are attributed to different definitions and
diagnostic criteria employed between studies. However, it would not be
surprising to expect an increase in the incidence and prevalence rates of this
disease over the next few years with the current wide spread use of corneal
topography leading to improved diagnosis13
. Keratoconus affects both genders,
although it is unclear whether significant differences between males and females
exist14
. Keratoconus, classically, has its onset at puberty and is progressive until
the third to fourth decade of life, when it usually arrests. It is most commonly
an isolated condition, despite multiple singular reports of coexistence with other
disorders.
Commonly recognized associations include Down syndrome, Leber‘s
congenital amaurosis, and connective tissue disorders. For example, patients
with advanced keratoconus have been reported to have a high incidence of
mitral valve prolapse. Atopy, eye rubbing, and hard contact lenses have also
been reported to be highly associated with this disorder15
.

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3. 2. CLINICAL CHARACTERISTICS
The ocular symptoms and signs of keratoconus vary depending on disease
severity. At incipient stages, also referred to as subclinical or forme fruste,
keratoconus does not normally produce any symptoms and thus can go unnoticed
by the patient and practitioner unless specific tests (i.e., corneal topography or
Pentacam) are undertaken for diagnosis15, 17
. Disease progression is manifested
by a significant loss of visual acuity which cannot be compensated with
spectacles.
The first symptom of Keratoconus is a deterioration of vision which usually
appears in one eye only as a result of regular or irregular myopic astigmatism.
Glare, ghost image, monocular diplopia, photophobia, and frequent changes of
glasses are usually first reported by patients (Edrington et al., 1995). The period
between the onset of disease and the first clinical signs or symptoms is very
difficult to detect. In the early stage, myopic astigmatism and a scissors motion
can be detected using retinoscopy, a circular shadow can be seen through
ophthalmoscopy, and irregular or distorted mires accompanied by an increase in
corneal steepness can also be seen using keratometry (Robinowitz, 1998).
In moderate to advanced stages, one or more of the following signs may be
detectable by biomicroscope slit-lamp examination of the cornea: stromal
thinning, conical protrusion (figure 1.A. and 1.B.), apical stromal scarring,
Fleischer’s ring, and Vogt’s striae (Edrington et al., 1995; Zadnik et al.,
1996). Fleischer’s ring is a yellowbrown to olive-green pigment forming an
incomplete annulus seen at the base of the cone as a result of haemosiderin
(iron) deposition in basal epithelial cells created by corneal stretching in the
advanced stage of Keratoconus (figure 1.C. and 1.D.). Vogt’s striae are fine
vertical lines, which represent folds in the posterior stroma and Descemet’s
layer and disappear transiently on gentle pressure (figure 1.E.). Further clinical
signs include Munson’s sign and Rizzuti’s sign (Maguire and Meyer, 1988).

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These two signs are useful confirmative external indicators associated with the
disease.
Munson’s sign is a V-shaped angulation of the lower eyelid in terms of the
upper lid rising when the patient looks downwards (figure 1.H.). Rizzuti’s sign
is a triangular focused beam seen near the nasal limbus, formed by lateral
illumination of the cornea in cases with severe Keratoconus.
One more clinical sign seen in the advanced stage is acute or hydrops
Keratoconus, characterised by a massive influx of aqueous humour into the
stroma as a result of a tear in Descemet’s membrane and endothelium (figure
1.I. and 1.J.). The cornea then becomes densely edematous, leading to a severe
reduction in visual acuity. Within 6 weeks, any endothelial damage has usually
healed by enlargement of nearby cells and the stretching of these endothelial
cells to cover the breaks. Tuft et al. (1994) assessed clinical factors associated
with the development of corneal hydrops in Keratoconus patients and found that
hydrops were more common in younger males and in subjects with severe
allergic eye disease. Further, corneal hydrops is frequently seen in cases of
Down’s syndrome (Bron et al., 1978).

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Figure 1. Key clinical signs of keratoconus.
A, B. Highlight corneal thinning and
conical protrusion visible in an
optical section in Keratoconus.
(Indicated by arrows).
C, D. Fleisher’s ring, a partial or complete
iron deposition ring in deep
epithelium encircling the base of the
cone, is visible (indicated by arrows)
using C. a cobalt blue filter and
D. white light
E. Vogt’s vertical striae are visible at the
corneal apex of a keratoconic cornea
(Indicated by arrow).
F, G. Show prominent corneal nerves
indicated by arrows (F. 20x, G. 40x
magnification).
H. Munson’s sign (conical protrusion
noted on down gaze).
I, J. Acute Corneal hydrops due to rupture
in Descemet’s membrane (I. 20x,
J. 10X magnification).

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3. 3. DIAGNOSIS OF KERATOCONUS
INTRODUCTION
CORNEAL CURVATURE CAN BE MEASURED BY:
 CORNEAL TOPOGRAPHY (Placido-disk based computer videokeratoscopes) (figure 2)
Corneal topography is becoming an invaluable clinical tool because it
provides information about corneal curvature which has direct relevance to
optical elements of the cornea beyond the central 3 mm measured by the
keratometer. However, the detection and identification of the very early stage of
Keratoconus and the ability to distinguish it from other disorders is still
difficult. As reported by Wilson (1991), prior to the introduction of the
videokeratoscope, the detection of early Keratoconus was one of the main
reasons for using Amsler’s Placido disc. It was used to monitor progressive
alterations in the anterior corneal surface in Keratoconus by monitoring the
uniformity mires of a Placido disc. In 1984, Klyce introduced a new computer-
based analysis of keratoscope images that produced three-dimensional wire
models of corneal surface distortion. This technique offered the opportunity to
evaluate the patterns of power distribution seen in the earliest stages of
Keratoconus. It also offered the opportunity for earlier diagnosis and better
understanding of the degree of corneal irregularity compatible with a given level
of visual function.
Maguire and Bourne (1989) used this procedure to detect the presence of
Keratoconus in patients without slit lamp or keratometry based evidence of
Keratoconus. They reported that corneal topography analysis systems were
useful in the detection and description of corneal irregularity in the early stages,
but only if used by an expert examiner. With the development of
computerassisted videokeratoscopes in the mid 1980s, it became apparent that
some corneas have the topographic features of mild Keratoconus in the absence
of other clinical signs (Maguire and Lowery, 1991; Harrison and Maguire,
1995). Rabinowitz and McDonnell (1989) developed algorithms for the detection
of Keratoconus that are available on some corneal topographers and made the
following observations: 18

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• Power differences are noted between the superior and inferior
paracentral corneal regions in Keratoconus and are measurable as the l-S
value.
• Central corneal power is higher in Keratoconus than normal eyes.
• There is a difference in the progression of corneal steepening in the two
eyes of a Keratoconus patient.
This approach permits a positive identification of early suspected
Keratoconus, if the central corneal power is greater than 47.2 D or if the l -S
value is greater than 1.4 D. It also generates a positive result for clinical
Keratoconus if the central corneal power is greater than 48.7 D or the l-S value
is greater than 1.9 D. A study was designed to evaluate the topography of a
large series of Keratoconus patients using computer-assisted topographic
analysis. This work indicated the technique had many potential applications for
the study of Keratoconus (Wilson et al. 1991). Other work using the same
procedure at two to three-month intervals for a two-year period on patients with
Keratoconus in one eye, showed no evidence of Keratoconus in the contralateral
eye (Maguire and Lowry 1991).
These findings pointed to the use of effective topography-assisted systems
in documenting subclinical cone progression. Further, they may be a useful tool
in the study of the true incidence and natural progression of subclinical
Keratoconus.
Maeda and colleagues (1994) developed an automated system to dif ferentiate
clinical Keratoconus from other corneal topographies using videokeratography.
They concluded that this system could be used to distinguish clinical
Keratoconus from other corneal topographies. In addition, this quantitative
classification method might also aid in refining the clinical interpretation of
topographic maps.
Finally, Dastjerdi and Hashemi (1998) utilised videokeratographs to map three
groups of patients (the first group were known Keratoconus, the second group

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were suspected, and the third group were normal). Using the highest rate of
steeping as a sole index compared with six other measures, and utilising a
discriminate analysis technique for a period of one year, their study showed
high power and efficacy in differentiating the first two groups of Keratoconus
from normal eyes (94.9% accuracy). The above literature indicated that the
authors used the highest reading (greatest power) on the topographic maps as an
index for the point of maximum steepness (peak of cone) on the surface of the
cornea to assess the existence of Keratoconus and its position. In other words
the colour-coded contour map of corneal powers conveys topographic
information using colour association and pattern recognition (figure 3).
Normal powers were shown as green, very low powers were shown as cool
or blue colours, and high powers were shown as warm or red colours (Klyce,
1984; Maguire et al, 1987).
In summary, the topography is designed to map the extent of astigmatism
on the surface of cornea, and to classify the stages of Keratoconus and monitor
its progression.
Figure 2 Figure 3

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CORNEAL THICKNESS CAN BE MEASURED BY:
Pachymetry (Greek words: Pachos = thick + metry = to measure) is term used
for the measurement of corneal thickness. It is an important indicator of health
status of the cornea especially of corneal endothelial pump function. It estimates
the corneal barrier and endothelial pump function. It also measures corneal
rigidity and consequently has an impact on the accuracy of intraocular pressure
(IOP) measurement. The normal corneal thickness varies from central to
peripheral limbus. It ranges from 0.7 to 0.9 mm at the limbus and varies 0.49
mm and 0.56mm at the centre. The Central corneal thickness (CCT) reading of
0.70 mm or more is indicative of endothelial decompensation. The mean CCT as
shown by various studies is 0.51 – 0.52 mm (standard deviation 0.02-0.04 mm).
 Factors affecting central corneal thickness:
The CCT was found to be higher in younger patients, male patients and
diabetic patients.
Central corneal thickness does not correlate with refraction or systemic
hypertension.
 Role in clinical practice
1. Assessing the thinness of the cornea as in corneal disorders like
Keratoconus, Keratoglobus, Post LASIK ectasia, Terrien’s and Pellucid
marginal degenerations.
2. Contact lens: To assess corneal edema and in orthokeratology.
3. Refractive surgeries: a) preoperative screening and b) treatment plan
of keratorefractive procedures like LASIK, astigmatic keratotomy, and
previously even prior to radial keratotomy.
4. Glaucoma: for applying correction factor in actual intraocular pressure
(IOP) determination.
5. Congenital Glaucoma: To assess the amount of corneal edema.

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Undoubtedly, central corneal thickness decreases in keratoconic corneas.
As regards the biomechanical properties of the cornea, scientists view the
stroma as primarily responsible for most of the biomechanical stability of the
cornea. In terms of Keratoconus, the thinking is that the apical corneal stroma
becomes weak due to thinning tissue. In advanced cases, the tissue begins to
bulge and consequently changes the shape of the cornea.
The progress of disease is associated with central corneal thinning and with
an increase in central corneal curvature (Insler and Cooper, 1986). In attempts
to measure the central and peripheral corneal thickness of 20 Keratoconus eyes
using ultrasound pachymetry Gromacki and Barr (1994) found that the average
central corneal thickness for Keratoconus corneas was 0.52 mm compared to
0.56 mm for normal corneas. Furthermore, there was no difference in peripheral
corneal thickness between Keratoconus and normal corneas.
However, ultrasound pachymetry is only capable of revealing average
readings of central corneal thickness (Wheeler et al. 1992), it does not allow the
identification of the thinnest corneal site. Consequently, central corneal
thickness and apical central thickness were measured using Pentacam and
ultrasonic pachymetry in one eye of 72 normal subjects and 64 eyes of 36
keratoconus patients (Gherghel et al., 2003). The study showed that the
Pentacam provided good agreement with ultrasonic pachymetry for norm al eyes.
In keratoconic eyes, however, Pentacam measurements were significantly lower
than those obtained by ultrasonic pachymetry. Using the Paradigm ultrasound
biomicroscope, Avitabile and coworkers (2004) sought to classify the stages of
Keratoconus based on corneal thickness of 60 eyes, and to measure central and
peripheral corneal thickness at different stages. They found that central corneal
thickness values ranged between 0.278-0.592 mm, whereas corneal peripheral
thickness values lay in the 0.475-0.992 mm range.

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 Techniques of Pachymetric Measurements2
There are two types of Pachymetric techniques:
A. Spot measurements: These technologies include traditional optical
pachymetry, specular and confocal microscopy, ultrasound pachymetry,
and optical low coherence reflectometry.
B. Wide area mapping: These provide the capability to map a wide area of
the cornea. Pachymetric mapping technologies include slit scanning
optical pachymetry and very high frequency ultrasound imaging.
Pachymetric mapping provides several advantages over spot
measurements. Mapping can reveal abnormal patterns such as
Keratoconus and pellucid marginal degeneration. Despite these
advantages, conventional ultrasound spot pachymetry is still the
standard because of its reliability, ease of use, and relatively low cost.
 ULTRASONIC PACHYMETRY (FIGURE 4)
This is the most commonly used method these days and is regarded as the
gold standard. In 1980, Henderson and Kremer introduced the ultrasonic
pachymeter.
Principle:
The ultrasonic pachymetry measurements depend on the reflection of
ultrasonic waves from the anterior and posterior corneal surfaces. It is the
measurement of the time difference (transit time) between echoes of ultrasonic
signal pulses from the transducer of the probe and the reflected signal from the
front and back surface of the cornea to the transducer.
Corneal thickness is calculated by following simple formula:
Corneal thickness = (Transit time + Propagation velocity)/2
The sound velocity through normal cornea is taken as 1640m/ sec. Kremer
et al selected this sound velocity because it gave him the average reading of
0.512±0.035mm which was same as given by optical pachymetry.

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There are 3 major components of Ultrasonic pachymeter:
a. Probe handle
It consists of a piezoelectric crystal which vibrates at frequency of 10 -
20MHz. This is a hand held probe which is very small, light and easier to
use clinically. Some probes also have a digital read outs where the
readings can be read directly.
b. Transducer
It sends ultrasound rays through the probe to the cornea and receives
echoes from the cornea.
c. Probe tip
The diameter of the tip should not be more than 2 mm, so that ultrasound
beam spreads over a lesser area and the place where the tip of the probe is
kept can be seen. The probe tip should be smooth enough to avoid damage
to the corneal epithelium. A wide probe tip and a wide transducer beam
reduce the accuracy of the corneal thickness reading.
When performing the measurement the probe tip has to be placed
perpendicular to the centre of cornea. As corneal thickness increase
peripherally, lateral displacement of the probe may cause elevated
readings as well as shift of the probe out of the correct perpendicular
position.
Figure 4

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Advantages
 Fast
 Simpler : therefore easier for paramedical staff to use
 Requires minimal observer judgment and is therefore consistent and
repeatable between observers thereby eliminating interobserver variation.
 Portable
 Dry (no coupling medium required)
 Can be used intraoperatively
Disadvantages
 Contact method
 Accuracy is dependent on the perpendicularity of the probe’s application
to the cornea.
 Reproducibility relies on precise probe placement on the center of the
cornea.
 Difficult to control the patients gaze during repeated measurements, so
that the placement of the probe is difficult to reproduce.
 There is variable sound speed in wet and dry tissues.
 Low resolution
 Not accurate in edematous corneas
Thus, to summarize, examiner’s experience can influence the reliability of
measurements.
 ELEVATION BASED TOPOGRAPHY
Measurement of Placido-disk based corneal topography and central
corneal thickness are widely used methods in the diagnosis of keratoconus,
however they are of limited use. Placido-disk based corneal topography only
examines the anterior surface of the cornea and alteration in the reference point
or viewing angle may result in inaccuracy of curvature measurement 19, 20
.
Ultrasound pachymetry, which is widely used for the measurement of central
corneal thickness, is a contact device and precise measurement depends on
correct probe alignment and centration 21
.

24. 23 | P a g e
With the advent of the Pentacam Comprehensive Eye Scanner (Oculus,
Wetzlar, Germany) anterior and posterior corneal surface elevation data
measurement and pachymetry map detection have become possible. Height data
give a more accurate representation of the true shape of the corneal surface
because they are independent of axis, orientation and position 10, 11, 19
. The
Pentacam have the advantage of being non-contact methods.
 PENTACAM
The Pentacam Rotating Scheimpflug tomographer (Oculus, Wetzlar,
Germany) (figure 5) utilises a combination of a slit illumination system and a
Scheimpflug camera using blue light emitting diodes (LEDs) (475 nm UV-free),
which rotates to analyse the anterior segment. It has a rotating Scheimpflug
camera that takes up to 50 slit images of the anterior segment in less than 2
seconds. Software is then used to construct a three dimensional image. A second
camera captures eye movements and makes appropriate corrections. It calculates
data for corneal topography (anterior and posterior corneal surface) and
thickness, anterior chamber depth (ACD), lens opacification and lens thickness.
It analyses the complete anterior segment, corneal topography,
quantification of the lens density, anterior chamber, angle measurements, and
utility to monitor new therapeutic modalities like collagen crosslinking
treatment for Keratoconus.
Figure 5

25. 24 | P a g e
Principle:
The Pentacam (Oculus Inc., Germany) is based on the true elevation
measurement and images the anterior segment (cornea + lens) of the eye by a
rotating Scheimpflug camera measurement which supplies pictures in three
dimensions. The centre of the cornea is measured very precisely because of this
rotational imaging process. The corneal thickness is displayed as a colour
image, showing the entire area from limbus to limbus.
Advantages:
 Noninvasive, non contact
 Even minute eye movements are captured and corrected simultaneously.
 It gives precise representation and repeatability.
 The high quality of the Scheimpflug image allows pre and post operative
monitoring as in the case of an intraocular contact lens.
Disadvantages:
It underestimates the corneal thickness in comparison to ultrasonic
pachymetry.
MAPPING KERATOCONUS BY PENTACAM
The posterior surface of the cornea usually reveals the first detectable
thinning, and protrusion of this surface. Nevertheless, the back surface of the
cornea is never as precise as the front, because its curvature and he ight are
calculated by looking through the front surface of the cornea, making the back
surface a virtual image.
In Keratoconus, the sagittal or tangential map, pachymetry map, and
posterior elevation map all show the same “hot spot” point (figure 6). A hot
spot in the same location on all three maps indicates an irregularity such as a
Keratoconus.
Screenings for Keratoconus are as follows:
1. Anterior and posterior elevation maps: In the anterior elevation map
differences between the best fit sphere and the corneal contour of less
than +12μm are considered normal, between +12μm and +15μm are

26. 25 | P a g e
suspicious, and more than +15μm are typically considered as keratoconus.
Similar numbers about 5μm higher apply to posterior elevation maps.
2. Anterior curvature map: The steepening of the cornea, irregular
astigmatism, inferior steepening (I – S difference), location of steepest
point and the thinnest point on the cornea may help in the diagnosis of
keratoconus.
Figure 6
BELIN – AMBROSIO ENHANCED ECTASIA (figure 7)
This new display combines elevation and pachymetry data. The
pachymetry progression analysis is known, and the elevation maps using the
best fit sphere (BFS) are displayed. It is extremely sensitive for early detection
and evaluation of Keratoconus and reliable detection of a forme fruste
Keratoconus in very early stages.
KAPOOR
ANU
19/06/1982
14/12/2013
Real position False placement

27. 26 | P a g e
The Belin/Ambrosio display is the first screening tool which represents
height data of the anterior and posterior corneal surface in combination with a
progression analysis of the corneal thickness. In addition to its overall more
precise Keratoconus detection this screening facilitates early detection in
particular. The corneal thickness progression analysis is calculated using
concentric rings, starting at the thinnest point and extending to the periphery.
The evaluation of deviations from the standard elevation map and the expanded
elevation map is made easier by displaying the results in green , yellow and red.
Figure 7
THICKNESS DISTRIBUTION MAP:
Corneal thickness progression graph detects a suspect abnormal abrupt
increase of the thickness values from the thinnest point towards the limbus.
Patient lines (red) should be between the lines and follow the curve of the
normative data. Prog. Index of the graph should be less than 1.2. (Figure 7)

28. 27 | P a g e
4. REVIEW OF LITERATURE
1. Evaluation of keratometric, Pachymetric and elevation parameters
of keratoconic corneas with Pentacam22
.
By: Miháltz K, Kovács I, Takács A, and Nagy ZZ.
Pub.: Cornea 2009; 28:976-80. IF: 2.106
PURPOSE: The purpose of this study was to evaluate the alteration of
keratometric, pachymetric, and elevation parameters of keratoconic and normal
corneas with the Pentacam Scheimpflug camera.
METHODS: Pentacam measurements were performed on 41 eyes of 24 patients
with keratoconus and 70 eyes of 41 normal subjects. In each eye, keratometric
values, central and minimal pachymetry, and anterior and posterior elevation
were evaluated. Receiver operating characteristic curves were used to compare
the sensitivity and specificity of the different parameters. Predictors of
keratometric, pachymetric, and elevation data were evaluated by logistic
regression analysis. Confirmatory factor analysis was performed in the KC
group to quantify the validity of critical parameters for keratoconus.
RESULTS: All parameters were significantly different in the keratoconus group
compared with the normal control group. Receiver operating characteristic curve
analyses showed the best predictive accuracy for posterior and anterior
elevation (0.97 and 0.96) followed by minimal and central pachymetry (0.89 and
0.88). The optimal cutoff point for posterior elevation was 15.5 micron for the
discrimination of keratoconus corneas from normal. Logistic regression analysis
showed best fit to the data for the model completed with the height data of the
Pentacam. Confirmatory factor analysis explained a 3-factor model satisfactorily
showing minimal pachymetry (-0.99), anterior elevation (0.98), and keratometry
(0.95) as the most representative clinical variables of the disease.
CONCLUSION: Posterior and anterior elevation, pachymetric, and keratometric
parameters measured by the Pentacam camera can effectively discriminate
keratoconus from normal corneas serving as a useful diagnostic tool for disease
staging.

29. 28 | P a g e
2. Corneal thickness measurements in normal and keratoconic eyes:
Pentacam comprehensive eye scanner versus and ultrasound
Pachymetry27
.
By: Omur Ozlenen Uc¸akhan, MD, Muhip Ozkan, PhD, Ayfer Kanpolat, MD.
J Cataract Refract Surg 2006; 32:970–977 Q 2006 ASCRS and ESCRS
PURPOSE: To compare central corneal thickness (CCT) measurements taken
with the Pentacam comprehensive eye scanner (CES) and ultrasound pachymetry
(UP) in normal and keratoconic corneas.
SETTING: Department of Ophthalmology, Ankara University School of
Medicine, Ankara, Turkey.
METHODS: In a prospective study, 2 CCT measurements were taken with the
Pentacam CES and UP in that sequence from 1 eye of 45 consecutiv e patients
with myopia (group A) and 62 consecutive patients with keratoconus (group B).
Eyes with keratoconus were further divided into 3 subgroups, mild, moderate,
and severe, according to the mean keratometry readings.
RESULTS: Pentacam CES (rZ 0.994) and UP (r Z0.993) demonstrated very high
and comparable reproducibility in group A. In group B, Pentacam CES displayed
better reproducibility (rZ0.988) than UP (r Z0.969). The mean CCT
measurements of Pentacam CES and UP were not significantly different in group
A (P Z 0.37) and in eyes with mild keratoconus (P Z 0.29), whereas significant
differences between all instrument pairs were evident in group B and in
moderate and severely keratoconic eyes (P<0.05). There were significant linear
correlations between CCT measurements of Pentacam CES and UP groups A, B,
and mildly keratoconic eyes (P<0.001).
CONCLUSIONS: Results suggest that whereas Pentacam CES and UP may be
used interchangeably in normal eyes in the clinical setting for the measurement
of CCT, one should be cautious interpreting corneal thickness data from
Pentacam CES and UP in eyes with keratoconus. Whereas, in normal and mildly
keratoconic eyes, Pentacam CES and UP demonstrated very high and comparable
reproducibility, in moderately keratoconic eyes, Pentacam CES readings showed
better reproducibility than UP.

30. 29 | P a g e
3. Mild topographic abnormalities that becomes more suspicious on
Scheimpflug imaging5
.
By: Wolf A, Abdallat W, Kollias A, Frohlich SJ, Grueterich M,
Lackerbauer CA.
Pub.: EJO 2009; 19(1):10-7
PURPOSE: Although several screening methods exist, postoperative corneal
ectasia after refractive surgery is a severe complication. One possibility for this
might be the fact that screening methods may fail in detection of preoperative
risk factors such as forme fruste keratoconus (FFKC).
METHODS: Retrospective evaluation of four cases that showed only mild
changes of FFKC on placido-based topography but revealed indicative findings
on Scheimpflug imaging (Pentacam®).
RESULTS: While in placido-based topography evaluation of corneal topography
did not show a clear FFKC, the evaluation of corneal topography on
Scheimpflug imaging together with the data of spatial corneal thickness revealed
distinctive FFKC in all cases presented.
CONCLUSIONS: Although both methods bear the risk of not detecting pre-
existing FFKC, Scheimpflug imaging seems superior to placido-based corneal
topography alone. (Eur J Ophthalmol 2009; 19: 10-7)
KEY WORDS: Scheimpflug imaging, Placido-based corneal topography, Forme
fruste keratoconus

31. 30 | P a g e
4. Reproducibility and repeatability of corneal thickness measurement
in keratoconus using the rotating Scheimpflug camera and ultrasound
pachymetry21
.
By: de Sanctis U, Missolungi A, Mutani B, Richiardi L, Grignolo FM.
Pub.: AJO 2007; 144(5):712-8
PURPOSE: To assess repeatability, reproducibility, and agreement of rotating
Scheimpflug camera (Pentacam Oculus, Wetzlar, Germany) and ultrasound
pachymetry in measuring central thickness of keratoconic corneas.
DESIGN: Method-comparison study.
METHODS: In 33 patients with keratoconus (one eye per patient), two
examiners each used both pachymetric methods to measure central corneal
thickness (CCT); in the same session, measurements then were repeated by
examiner 1 (A.M.). The difference between two examiners and between first and
second measurements by examiner 1, with both methods and the difference
between the two pachymetric methods in measuring central thickness of
keratoconic corneas were noted.
RESULTS: With the rotating Scheimpflug camera, inter-examiner correlation
was higher (intra-class correlation coefficient [ICC], 0.98 vs. 0.76) and inter-
examiner variability was lower (95% limits of agreement [95% LoA], -14.8 to
13.8 μm vs. -18.0 to +49.5 μm) than with ultrasound pachymetry. Both methods
showed close first to second-measurement correlation (ICC, > 90), but the
rotating Scheimpflug camera had lower variability (95% LoA, -14.5 to 14.2 μm
vs. -27.4 to 26.0 μm). Mean CCT was 478.9 ±34.6 μm with the rotating
Scheimpflug camera and 486.6 ±30 μm with ultrasound pachymetry. Although
the mean difference was small (-7.8 μm), the 95% LoA (-43.8 to 28.2 μm)
showed that the difference between the two methods can be considerable.
CONCLUSIONS: In keratoconic corneas, the rotating Scheimpflug camera
provides measurements of central thickness that are more reproducible and
repeatable than those obtained with ultrasound pachymetry. The rotating
Scheimpflug camera seems to be suitable for disease staging and follow-up,
when corneal thickness measurements may be repeated over time by different
examiners.

32. 31 | P a g e
5. MATERIALS AND METHODS
5. 1. Study Design
This is a prospective, randomized, hospital based, comparative study done to
find the prevalence of keratoconus eyes at our centre within a period of 6 month
and to compare the accuracy of Pentacam with Ultrasound pachymetry and
corneal Topography in assessing corneal thickness (CT) and corneal curvature
respectively, in 60 eyes of 30 patients diagnosed to have Keratoconus.
INCLUSION CRITERIA:
Both eyes of every patient have undergone a complete ophthalmologic
evaluation. If all of the following conditions are satisfied, the patient is eligible
for the study:
• Age: ≥10 as smaller children will not cooperate well with the instruments to
40 years as beyond this age the keratoconus will be in advanced stage and we
are concerned in identifying mild to moderate stage.
• Irregular corneal surface in either eye determined by distortion of
keratometric mires, of the Retinoscopic scissor reflex, or higher astigmatism
in prescription.
• Either Vogt’s striae in the deep stroma or Munson’s sign or corneal scarring
characteristic of keratoconus in either eye.
• No gender preference.
EXCLUSION CRITERIA:
If a patient has the following condition she/he is excluded from the Study:
• Age: below 10 years and above 40 years
• Bilateral corneal transplants.
• Non-keratoconic corneal disease in both eyes: Pellucid Marginal
Degeneration, Terrien’s Marginal Degeneration, Keratoglobus.

33. 32 | P a g e
5. 2. Subjects and Methods
All patients attended a Lasik centre for periods of 6 month (November 2013 -
April 2014) were studied. Total no. of patients examined were 415 in Lasik
centre. In all patients we did examination with all 3 instruments and patients
who showed signs of Keratoconus were recruited and further compared in detail
by all three instruments in relation to their accuracy for measuring CCT and
corneal curvature. The eye evaluation for Keratoconus by Pentacam, Corneal
topography and Pachymetry for each patient was achieved at a single session
lasting approximately 30 minutes. We have measured average and steep corneal
curvature both, because highest rate of steepening may be a useful measure for
keratoconus screening.
The clinical assessment routine for each patient included the following:
1. Demographic details:
For identification of patients and statistical analysis: history regarding name,
age, gender, residence, occupation, case register no. was noted.
2. Preliminary examinations:
In all patients visual acuity, refraction and slit lamp for anterior segment was
evaluated. The participants were informed about the purpose of the study and
gave informed consent before inclusion.
3. Corneal topographic measurements:
Corneal topographic measurements were taken with the Oculus corneal
topographer (Oculus Easygraph Topographic Modeling System). The corneal
topographer system consists of the topographer itself and a personal computer.
The software is almost fully automated. After the patient’s data were entered,
the program changed to imaging mode. The patients were instructed to place
their chin in the chin rest and press their foreheads against the forehead straps,
and asked to keep both eyes open and fixate on the target, in the centre of the
red fixation beam. The image was then focused and centred manually by moving
the joystick in the respective directions. Topographic images were taken at 5 to
6 seconds after a complete blink, when the tear film layer is the most stable .

34. 33 | P a g e
4. Pentacam measurements:
All eyes were examined with the Pentacam (Oculus Inc.). The readings were
taken as recommended in the instruction manual. The Pentacam system consists
of the Pentacam itself and a personal computer. The software is almost fully
automated. After the patient’s data were entered, the program changed to
imaging mode. Briefly, the patients were instructed to place their chin in the
chin rest and press their foreheads against the forehead straps, and asked to keep
both eyes open and fixate on the black target, in the centre of the blue fixation
beam. The examiner sees a real-time image of the patient’s eye on the computer
screen. The image was then focused and centred manually by moving the
Pentacam in the respective directions. Markings on the screen indicate the
direction; the operator should move the joystick of the camera. As soon as the
image is perfectly aligned, the patient was asked not to move and to keep his or
her eye open, and the scan was started. After attaining perfect alignment, the
instrument automatically capture 25 Scheimpflug images of anterior segment
within 2 seconds. For each eye one high quality image was recorded.
5. ULTRASOUND PACHYMETRY:
The cornea was then anaesthetized with topical 0.5% proparacaine and five
reading were taken with Ultrasound pachymeter (Sonomed). The patients were
instructed to look straight ahead and fixate on a target. The hand held probe was
applied perpendicularly on the centre of the cornea under anaesthesia. All five
pachymetry readings were carried out by one examiner. In all cases, the fi ve
measurements were used for further comparative analysis.
In our study the following data were then exported to a Performa sheet :
Keratometry values in the flat (K1) and steep (K2) meridian, corneal thickness
at the centre (central pachymetry) and at the thinnest point of the cornea
(minimal pachymetry) and the topographical Keratoconus classification Indices.

35. 34 | P a g e
PROFORMA
Pt. Name: Reg. No.
Age/Sex: Occupation:
Presenting complains:
INVESTIGATIONS
OD OS
Ant. Seg. Examination:
Pentacam __________ __________
Central pachymetry:
Ultrasound
Pachymeter __________ __________
Pentacam
K1/K2/Axis __________ __________
Corneal Curvature:
Corneal
Topography
K1/K2/Axis __________ __________
Topographical Keratoconus
Classification (TKC): __________ __________

36. 35 | P a g e
6. OBSERVATION & DISCUSSION
The results of various observations were documented and charted.
TABLE 1- Gender Distribution
Gender No. %
MALE 13 43.33
FEMALE 17 56.67
TOTAL 30 100
In our study, out of 415 patients 30 participants were enrolled having
keratoconus, where population included were 13(43.33%) males and 17(56.67%)
females’ subjects, the incidence was 7.22%. The incidence and prevalence of
keratoconus in the general population has been estimated to be between 5 and
23, and 5.4 per 10,000, respectively (Barr JT, Wilson BS, Gordon MO, et al). A
low incidence of the disease is apparent in Japan, Taiwan, and Singapore (Khoo
1989; Chen et al., 2001). The female ratio was slightly higher as female were
more concerned about their cosmetic, thus coming for Lasik treatment.
Figure 1- Pie chart showing the gender distribution
56.67 %
Gender
MALE
FEMALE

37. 36 | P a g e
TABLE 2- Age Distribution
Age No. %
11-15 YRS 1 3.33
16-20 YRS 7 23.33
21-25 YRS 13 43.33
26-30 YRS 6 20
31-35 YRS 1 3.33
36-40 YRS 2 6.67
The age of the subjects ranged from (11 to 40 years) with the mean age of 23.9
years ± 5.7. Amongst them the prevalence rate was 43.33% i.e. higher at the age
of 21 to 25 years who were diagnosed with Keratoconus. The majority of
patients coming for Lasik workup were concerned about cosmetics at the time of
marriage that were having the age group between 21 – 25 years.
Figure 2- Column chart showing the age distribution
0
2
4
6
8
10
12
14
11-15
years
16-20
years
21-25
years
26-30
years
31-35
years
36-40
years
1
7
13
6
1
2
No.ofPatients
AGE
Age Distribution

38. 37 | P a g e
TABLE 3- Mean Corneal thickness in 60 Eyes
Instruments Mean corneal thickness (μ) P - Value
ULTRASOUND PACHYMETER
503 ± 50.04 (S.D.)
0.0001
PENTACAM 499 ± 50.32 (S.D.)
With the help of statistics by using Paired t-test 23, we found the p-value
0.0001 which is < 0.05, thus the difference found is statistically significant.
The mean central corneal thickness found with ultrasound pachymetry was 503 ±
50.04µm and with Pentacam was 499 ± 50.32µm which was slightly lesser. The
Pentacam gives lesser corneal thickness as it measures the thinnest location than
ultrasound pachymetry which indicates the possibility of corneal ectasia.
Gherghel D, Hosking SL, Mantry S, Banerjee S, Naroo SA, Shah S. 26
found
that more than one third of subjects with KCN developed manifest KCN in the
other eye over 8 years. These authors reported the mean central corneal
thickness found with ultrasound pachymetry was higher i.e. 510 ± 49.24µm and
with Pentacam was 491 ± 51.32µm which was slightly lesser, which co-relate
with our study.
In another study, based on topographic maps from the Pentacam, Ucakhan et
al stated that KCN should be highly suspected in eyes with anterior elevation
greater than 15 µm and posterior elevation greater than 20 µm, corneal thickness
less than 500 µm. Subjects who had anterior elevation between 12 and 15 µm,
posterior elevation between 15 and 20 µm with a corresponding location of
thinnest pachymetry point less than 500 µm were diagnosed as KCN suspect , but
reported that the Pentacam gives thinnest pachymetry at the apex of keratoconus
than the ultrasound pachymetry, as the examiner was not aware of keratoconus
apex.

39. 38 | P a g e
However, to know whether Pentacam or Ultrasound pachymetry is better for
measuring corneal thickness in Keratoconus eyes, we have tested the Co -
efficient of Variation statistically, which was found to be:
C.V1 = 83.4088(Pentacam) and C.V2 = 83.8738(Ultrasound Pachymetry)
Therefore, statistically it was proved that Co-efficient of Variation of
Pentacam < Ultrasound pachymetry which means Pentacam is better option in
finding corneal thickness in Keratoconus eyes than Ultrasound pachymetry.
Figure 3- Column chart showing the Mean Corneal Thickness in 60 eyes in
microns.
496
498
500
502
504
Ultrasound Pachymeter Pentacam
CornealPachymetry
Instruments
Mean corneal thickness (μ)

40. 39 | P a g e
TABLE 4 – No. of eyes diagnosed Keratoconus on Pachymetry finding
Instruments No. of eyes Percentage (%)
ULTRASOUND PACHYMETER 32 53.33
PENTACAM 60 100
According to pachymetry findings, pentacam was able to diagnose keratoconus
in all the eyes i.e. 100% while ultrasound pachymetry was able to detect in only
32 eyes i.e. 53.33%, thus were under diagnosed. The difference found is
significant when testing with two different pachymetry instruments; this means
pentacam was more consistent in diagnosing keratoconus.
Figure 4 – No. of eyes diagnosed Keratoconus on Pachymetry finding.
0
10
20
30
40
50
60
Ultrasound
Pachymeter
Pentacam
32
60
No.ofeyes
Instruments
No. of eyes
Ultrasound Pachymeter
Pentacam

41. 40 | P a g e
TABLE 5 – Mean of average Corneal curvature readings in Dioptres
Instruments MEAN of Avg. Corneal Curvature Reading (D) P-Value
CORNEAL TOPOGRAPHY
45.82 ± 2.92 (S.D.)
0.768206
PENTACAM 45.79 ± 3.23 (S.D.)
With the help of statistics by using Paired t-test 23, we found the p-value
0.768206 which is > 0.05, thus the difference found is statistically insignificant.
The mean Avg. corneal curvature found with corneal topography was 45.82 ±
2.92D and with Pentacam was 45.79 ± 3.23D which was slightly lesser.
However, to know whether Pentacam or corneal topography is better for
measuring corneal curvature in Keratoconus eyes, we have tested the Co-
efficient of Variation statistically, which was found to be:
C.V1 = 6.3771(Pentacam) and C.V2 = 7.0752 (Corneal topography)
Therefore, Co-efficient of Variation of Pentacam < Corneal topography which
means Pentacam is better option in finding corneal curvature in Keratoconus
eyes than Corneal topography.
Figure 5- Column chart showing the Mean Avg. Corneal Curvature.
45.77
45.78
45.79
45.8
45.81
45.82
Corneal
Topography
Pentacam
45.82
45.79
CornealAvg.Curvature(D)
Instruments
Mean of Avg. Corneal Curvature
Corneal Topography
Pentacam

42. 41 | P a g e
TABLE 6 – Mean of Steep Corneal curvature readings in Dioptres
Instruments MEAN of Steep Corneal Curvature Reading (D) P-Value
CORNEAL TOPOGRAPHY
47.03 ± 3.60 (S.D.)
0.542775
PENTACAM 46.96 ± 3.88 (S.D.)
With the help of statistics by using Paired t-test 23, we found the p-value
0.542775 which is > 0.05, thus the difference found is statistically insignificant.
The mean steep corneal curvature found with corneal topography was 47.03 ±
3.60D and with Pentacam was 46.96 ± 3.88D which was slightly lesser.
In the study done by Saad A, Gatinel D25
, The mean +/- SD of highest rate of
steepening was 3.60 +/- 1.70 D/mm (range 1.59 to 7.53 D/mm) in the clinically
obvious keratoconus group, 1.59 +/- 0.21 D/mm (range 1.35 to 1.98 D/mm) in the
keratoconus suspect group, and 0.72 +/- 0.31 D/mm (range 0.18 to 1.63 D/mm) in
normal eyes. There was a statistically insignificant difference in the means of
highest rate of steepening in the Pentacam and corneal topography (p > 0.05). He
concluded that the highest rate of steepening may be a useful measure for
keratoconus screening with corneal topography.
However, to know whether Pentacam or corneal topography is better for
measuring corneal curvature in Keratoconus eyes, we have tested the Co -
efficient of Variation statistically, which was found to be:
C.V1 = 7.5955 (Pentacam) and C.V2 = 8.2024 (Corneal topography)
Therefore, Co-efficient of Variation of Pentacam < Corneal topography which
means Pentacam is better option in finding corneal curvature in Keratoconus
eyes than Corneal topography.

43. 42 | P a g e
Figure 6- Column chart showing the Mean steep corneal curvature.
46.9
46.95
47
47.05
C T Pentacam
47.03
46.96
CornealSteepCuravture(D)
Instruments
Mean of steep corneal curvature
C T
Pentacam

44. 43 | P a g e
7. SUMMARY
In this prospective, randomized, hospital based and comparative study, 415
patients were examined within 6 months from which 30 patients with
Keratoconus were detected.
The population included were 13(43.33%) males and 17(56.67%) females’
subjects ranged from (11 to 40 years) with the mean age of 23.9 years ± 5.7.
The incidence in our setup was about 7.22% and the prevalence rate was
43.33% i.e. higher at the age of 21 to 25 years who were diagnosed with
Keratoconus.
Again, Ultrasound pachymetry was only able to detect 32 eyes with Keratoconus
thus 28 eyes were under diagnosed from it while Pentacam was able to detect all
60 eyes of keratoconus.
The p-value was 0.0001 which is < 0.05, i.e. statistically significant when
testing with two different pachymetry instruments, at 5% level of significance
and the mean central corneal thickness found with ultrasound pach ymetry was
503 ± 50.04µm and with Pentacam was 499 ± 50.32µm .
Mean average and mean steep corneal curvature found with corneal topography
was 45.82 ± 2.92D and with Pentacam was 45.79 ± 3.23D and 47.03 ± 3.60D
and with Pentacam was 46.96 ± 3.88D respectively.
When measuring average and steep corneal curvature, the p-value was 0.768206
and 0.542775 which is > 0.05 respectively, thus the difference found is
statistically insignificant when testing with two different corneal curvature
measuring instruments, at 5% level of significance.

45. 44 | P a g e
8. CONCLUSION
Early diagnosis of KCN is an important clinical issue because the incidence
being 7.22% in our setup. We also know that cross- linking can halt the
progression of this ectatic disease. Instruments which diagnose Keratoconus at
early stage can avoid relative blindness due to Keratoconus. By halting
Keratoconus to go into its last stage, we can decrease the incidence of
keratoplasty, the last choice of treatment. The study clearly proves the
superiority of Pentacam in accurate early diagnosis of keratoconus in
comparison to corneal topography and Ultrasound pachymetry by 50%.
Though the instrument is 15 times more costly then Ultrasound pachymeter, it is
recommended at centres where premium Lasik surgeries are performed.

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