It is a clinical entity characterized by
noninflammatory and noninfective, progressive,
bilateral thinning of the cornea with ectasia of
This is mostly bilateral condition, girls between 15-
20 years affected more, overall incidence rate
estimated to be 0.15 to 0.20 percent.
It manifests by adolescence, resulting in
considerable visual impairment owing to the
development of high degree irregular myopic
Keratoconus is classified into four stages by
Krumeich et al.
Eccentric corneal steepness
Myopia and/or astigmatism < 5D
Corneal radius ≤ 48D
Vogt’s striae - no corneal scar
Myopia and/or astigmatism > 5D < 8D
Corneal radius ≤ 53 D
No corneal scar
Corneal thickness ≥ 400 µm
Definite etiology is unknown. 95% of patients do not show
evidence of specific hereditary pattern. Pattern of
inheritance is variable. Several theories have been put
forward to explain the etiology of keratoconus.
Alteration in the levels of following enzymes have been
Increased level of epithelial lysosomal enzymes.
Decreased level of alpha-1 proteinase inhibitor in the
Decreased levels of glucose-6 phosphate dehydrogenase in
CONNECTIVE TISSUE ABNORMALITY THEORY
There is association of keratoconus with some connective
Due to the occasional association of trisomy-21 with
keratoconus, genetic abnormality may be the cause.
It is proposed because of the manifestations of the disease
Habitual eye rubbing in some diseases like vernal catarrh,
Down syndrome and poorly sighted patients of Leber’s
tapetoretinal degeneration are associated with
Gradual decrease in vision, photophobia,
monocular diplopia or monocular polyopia.
Severe photophobia and watering is seen in cases
of hydrops. Particularly adolescent females are
There is conical protrusion of the cornea with
central thinning and the apex of the cone is usually
Munson’s sign is a V-shaped conformation
of the lower lid produced by the ectatic cornea
Rizzuti’s sign is a sharply focused beam of
light near the nasal limbus, produced by
lateral illumination of the cornea in patients
with advanced keratoconus.
Slit lamp examination
The Fleischer ring is a yellow-brown to
olive-green ring of pigment which may or
may not completely surround the base of
Formed when hemosiderin (iron) pigment
is deposited deep in the epithelium
Fleischer's ring often becomes thinner and
more discrete with progression
Seen approximately 50% of all cases.
Locating this ring initially may be made easier by
using a cobalt filter and carefully focusing on the
superior half of the cornea's epithelium.
Once located, the ring should be viewed in white
light to assess its extent.
Lines of Vogt:
Small and brushlike lines, generally vertical but they can be
Found in the deep layers of the stroma and form along the
meridian of greatest curvature.
Disappear when gentle pressure is exerted on the globe
through the lid.
Significant thinning (up to 1/5th cornea thickness)
in the advanced stages of the disease and a
diagnostic criterion based on comparison of
central and peripheral corneal thickness has been
Additionally, as the disease progresses, the cone is
often displaced inferiorly. The steepest part of the
cornea (apex) is generally the thinnest.
Sub-epithelial corneal scarring, not generally seen
early, may occur as keratoconus progresses because
of ruptures in Bowman's membrane which is then
filled with connective tissue
Deep opacity of the cornea are also common in
Corneal hydrops occurs in advanced cases, when
Descemet's membrane ruptures, aqueous flows into
the cornea and reseals
Keratoconus patients who are having an acute
episode of corneal hydrops report a sudden loss of
vision and a visible white spot on the cornea.
Corneal hydrops causes edema and opacification.
As Descemet's regenerates, edema and opacification
decreases. Occasionally, hydrops can benefit
keratoconus patients who have extremely steep
corneas. If the cornea scars, a flatter cornea often
results, making it easier to fit with a contact lens.
An increased incidence of hydrops has also been
reported in keratoconus patients with Down's
Early keratoconus usually manifests as a small
island of irregular astigmatism in the inferior
As the cornea bulges outward, the amount of
astigmatism increases due to the progressive
distortion of the corneal surface.
These changes can easily be seen as irregular mires
on keratometry readings and on corneal
Many objective signs are present in keratoconus.
Retinoscopy shows a scissoring reflex.
On direct ophthalmoscopy there is a dark round
shadow in the corneal midperiphery due to total
internal reflection of the light surrounding the
central bright red fundus reflex and separating it
from the normal red peripheral reflex. It is called
a Charleux oil droplet reflex.
The photokeratoscope or topographer placido disc
can provide an overview of the cornea and can show
the relative steepness of any corneal area.
There is even separation of the rings in the spherical
In astigmatic cornea uneven spacing of the
rings,especially inferiorly-in the keratoconic cornea
should be noted
The central rings may show a tear-drop configuration
With the handheld keratoscopes, such as the Klein
keratoscope, early keratoconus is characterized by a
downward deviation of the horizontal axis of the
Placido disk reflection
The Keratometer also aids diagnosis.
o Classification based on keratometry-
1. Mild- <45D in both meridians
2. Moderate- 45-52D in both meridians
3. Advanced- >52D in both meridians
4. Severe- >62D in both meridians
The initial keratometric sign of keratoconus is absence of
parallelism and inclination of the mires. These can easily
be missed in mild or early cases.
COMPUTER ASSISTED VIDEO KERATOSCOPY
It is one of the most important diagnostic aids for
very early as well as abortive forms of keratoconus
in the other eye of the patients with unilateral
keratoconus or in the family members.
Data of videokeratoscopic image are analyzed by
computers and depicted as color coded maps. Red
color indicates myopic refraction or ectasia and
blue color indicates hypermetropic refraction or
flattening of the cornea.
Slit lamp pachymetry shows thinning in the centre of the
apex. Ultrasonic pachymetry shows exact thickness of
cornea at different places.
Thinning in the inferior quadrant can be diagnostic of
keratoconus. Central or paracentral corneal thickness of
less than 450 µm is abnormal.
If the reading decreases by nearly 20 µm towards the
inferior periphery on successive pachymetric readings, it is
suspicious of keratoconus. Increase in the progressive
thinning of the cornea is a true index of keratoconus.
Provides a color coded map of
the corneal surface.
The power in diopters of the
steepest and flattest meridians
and their axes are calculated
Steep curvatures are marked
orange or red
Flat curvature in blue or violet
Normal curvatures in green or
Keratoconus is a clinical diagnosis and Forme Fruste
KC is a subtle topographic abnormality before
clinical manifestation of the disease.
The aim of topography and tomography in refractive
surgery clinic is to rule out keratoectatic disease
either in form of frank keratoconus or subtle FFKC
as they are contraindications to the procedure.
The suspicious signs for keratoconus include:
Axial map abnormalities
1. K greater than 48 D.
2. Skewed radial axis greater than 21 degrees.
3. Inferior -Superior ratio greater than 1.42D.
4. Corneal astigmatism greater than 6 D.
5. Against the rule astigmatism.
6. Superior-Inferior difference at the 5-mm zone >2.5
On the elevation maps
1. Isolated island or tongue-like extension on either surface
2. Elevation values greater than 12 microns on the anterior elevation
map in the central 5 mm.
3. Elevation values greater than 15 microns on the posterior elevation
Pachymetry/corneal thickness map: On Scheimpflug devices
1. Thinnest location less than 470 microns.
2. Displacement of the thinnest point >500 microns from the center.
3. Pachymetry difference asymmetry in two eyes at thinnest point >30
4. S-I difference at the 5 mm circle >30 microns.
5. Cone-like pattern on the thickness map.
The most elevated points on the anterior and the
posterior elevation maps should be correlated to the
highest power on Axial/Saggital curvature map and
the thinnest point on the global pachymetry map.
If all the above match, it is called as the “fourpoint
touch” and is a hallmark of suspect cornea, especially
if the apex is decentered by more than 500 microns
and the peripheral thickness readings of the upper
and lower half at the 7-mm zone also show a
significant difference of greater than 100 microns.
In patients who have never worn contact lenses .
Occur due to basal epithelial cell drop out as a result
the epithelium slides from the periphery as the
Thus a hurricane, vortex or swirl stain may occur.
Rabinovitz criteria for diagnosis of keratoconus
1. Central corneal power >47.2D
2. Inferior superior dioptric assymetry over 1.2D
3. Skewed radial axes of astigmatism by more than
4. Difference in central power of more than 1D
between the fellow eye.
This is due to thinning of periphery of the cornea which
gradually progresses towards the centre. It is present at or soon
after birth. So it is thought to be a developmental anomaly.
Perforation can occur in this condition with minimal ocular
2. POSTERIOR KERATOCONUS
It is nonprogressive, dome shaped posterior excavation in the
cornea which may be small and circumscribed( keratoconus
posticus circumscriptus) or may be diffuse( keratoconus
posticus totalis). It is considered to be a congenital defect.
Origin is prior to 5th or 6th month of gestation. Traumatic
etiology is also reported.
3. PELLUCID MARGINAL DEGENERATION
It is a bilateral peripheral corneal ectatic disorder
characterized by a band of thinning of 1-2 mm width
typically in the inferior cornea. Maximum corneal
protrusion occurs superior to the area of thinning.
There is no other abnormality and it occurs in 2nd to 5th
Mild keratoconus can be corrected with spectacles.
Retinoscopy is difficult; a normal subjective
refraction is required.
Monocular keratoconus is usually best dealt with
using spectacle correction.
In this group of patients, motivation for contact lens
wear tends to be poor.
Contact lenses are considered when vision is not correctible
to 6/9 by spectacles and patients become symptomatic.
Rigid gas permeable (RGP) contact lenses are the lenses of
The aim is to provide the best vision possible with the
maximum comfort so that the lenses can be worn for a long
period of time.
Based on shape of cone
Nipple cone : small diameter (5 mm.); round shape; easiest
to fit with contact lenses
Oval large diameter(>5 mm.); often displaced inferiorly;
more difficult to fit with lenses
Globus largest diameter (>6 mm.); 75% of cornea affected;
most difficult to fit with lens
1. Three-point-touch design
Three-point-touch actually refers to the area of apical
central contact and two other areas of bearing or contact at
the mid-periphery in the horizontal direction.
The three-point-touch design is the most popular and the
most widely fitted design
The aim is to distribute the weight of the contact lens as
evenly as possible between the cone and the peripheral
The ideal fit should show an apical contact area of 2-
3mm with mid-peripheral contact.
Adequate edge clearance is required to ensure tear
2. Apical clearance
In this type of fitting technique, the lens vaults the cone and
clears the central cornea, resting on the paracentral cornea.
These lenses tend to be small in diameter and have small
The potential advantages of reducing central corneal
scarring are outweighed by the disadvantages like poor
tear film, corneal oedema, and poor visual acuity as a result
of bubbles becoming trapped under the lens.
3. Flat fitting
The flat fitting method places almost the entire weight of the lens on
The lens tends to be held in position by the top lid.
Good visual acuity is obtained as a result of apical touch.
Alignment can be obtained in early keratoconus; however, flat fitting
lenses can lead to progression/ acceleration of apical changes and
This type of fitting is useful where the apex of the cone is displaced.
Piggy back lenses - RGP-CL over a SOFT CL
Can be used in pts who are uncomfortable with RGP wear,
more so in pts prone to epithelial erosion at apex of cone
ROSE-K design RGP -are specially designed for
keratoconic eyes with a diagnostic set of 26 lenses with base
curves ranging from 5.1 to 7.6 mm in 0.1 increments, a std
lens diameter of 8.7mm
Scleral lenses play a very significant role in cases of
advanced keratoconus where corneal lenses do not
work and corneal surgery is contra-indicated.
Scleral lenses completely neutralise any corneal
irregularity and can help patients maintain a normal
quality of life
Custom made lens
Two zones in the peripheral posterior curvature
a) Central zone : to vault steep central cornea .It is of
varying steepness depending of the patients cornea.
b) Peripheral zone is with a 45D curvature designed to
vault the mid periphery and limbal cornea
Boston scleral lens prosthetic device
Fluid ventilated scleral lens
Designed to enclose a bubble free reservoir of fluid
over the corneal surface
Series of breaches are created between haptic
bearing surface of the lens and underlying sclera.
This will facilitate the aspiration of surface tears into
the reservoir so that intrusion of air bubble during a
blink is prevented.
Shape of haptic confirms exactly to that of
underlying sclera to maintain functionality and
prevents intrusion of air bubbles.
Collagen cross linking
A newer and less invasive technique that shows promise in
keratoconus management is combined riboflavin-ultraviolet
type A rays( UVA ) collagen cross-linking.
This procedure consists of photopolymerization of corneal
stroma by combining vitamin B2 (photosensitizing
substance) with UVA.
This process increases rigidity of corneal collagen and thus
reduces the likelihood of further ectasia.
•Using topical anaesthesia, 7mm circle is marked on the
cornea using a thornton marker.
•Epithelium of the marked area is scraped off using a
•A corneal abrasion is created to facilitate riboflavin
diffusion into the cornea.
•One drop of riboflavin 0.1% and 20% dextran
ophthalmic solution is instilled topically in the eye every
2 minutes for 30 minutes.
•At the end of the 30-minute pretreatment period, the eye
is examined with blue light for the presence of a yellow
flare in the anterior chamber, indicating adequate
riboflavin saturation of the corneal tissue.
When the yellow flare in the anterior chamber is confirmed,
the eye is aligned under the UV-A light with the treatment
plane at 50 mm from the UV-A beam aperture. Focussed on
the apex of cornea at a distance of 10-12m to obtain a
radiant energy of 5.4J/cm2 for 5 min
The correct aperture setting is selected for the size of the
eye; the eye is irradiated for 30 minutes, during which time
instillation of riboflavin is continued (one drop every 5
After completion of the procedure,eye is washed with
BSS , an antibiotic drop is instilled and a bandage
contact lens is applied.
The contact lens is removed once the abrasion has
Postoperative medications include an antibiotic and
a steroid for 2 weeks postoperatively.
LASIK Xtra basically means LASIK combined with C3R to treat
Keratoconus and also for ectasia following LASIK surgery.
LASIK Xtra embodies a proper evolution of LASIK technique, the
refractive surgery technique which has received the most
enthusiastic acclaim worldwide. This technique uses the excimer
laser to remodel the curve of the cornea and surgically correct
myopia, hypermetropia, astigmatism and presbyopia in a rapid and
Just like LASIK procedure, the LASIK Xtra technique is also
successfully employed to re-treat previous interventions that were
partly or incompletely satisfactory. Generally, the procedure is
bilateral, i.e. the sight defect is corrected in both eyes in a single
It is pain-free, both during and after the procedure.
In addition to standard LASIK results, the LASIK Xtra
technique restores the strength of corneas weakened by
It enables normal activity to be resumed immediately:
e.g. work and sport.
Furthermore, bilateral correction also notably facilitates
WHO CAN USE LASIK XTRA?
The ideal candidate for LASIK Xtra has a stable refraction,
healthy corneas and certain physiological characteristics
(essentially, an adequate corneal thickness); in addition the
candidate must be highly motivated to reduce or eliminate
any dependence on glasses and lenses.
There must be no other eye diseases present.
For women at an advanced stage of pregnancy, it is preferable
that they do not undergo laser sight correction until their
eyesight stabilises, after the birth.
Previous surgery is not a contraindication. Indeed, LASIK
Xtra often perfects unsatisfactory results of previous surgery.
LASIK Xtra strengthening effect allows to broaden the
inclusion criteria for potential patients, opening the
possibility for many ineligible LASIK patients to become
candidates for LASIK Xtra – although this evaluation is
specifically carried out by the surgeon on a case-by-case
To assess suitability for the procedure and the nature of
the eyesight defect, it is indispensable that the patient
undergo a thorough preoperative check. On the basis of
this the specialist can plan a tailor-made treatment.
RISKS AND COMPLICATIONS
With the LASIK technique, no major or serious events have ever
been reported, involving loss of the eye or of eyesight. Infection is
extremely rare, but can be resolved with antibiotic treatment.
On rare occasions it may be the case that when vision has settled,
the results obtained do not fully meet expectations. This depends on
the natural reactivity of the eye which, if the treatments are equal,
differs from person to person.
In these rare cases, termed “under-corrections” or “over-
corrections”, the extreme flexibility of the LASIK Xtra technique
allows for a subsequent intervention to perfect the results obtained,
with no risk for the patient
Intracorneal stromal rings
Act as passive spacing agents which flatten the cornea
Made of PMMA
Amount of correction depends on the ring thickness, more
thicker the ring more correction.
On insertion they shorten the arc of ant corneal surface, iron out
gross irregularities and in effect create a second limbus.
Various corneal ring-kerarings, intacs.
An important potential benefit of treating
keratoconus with INTACS inserts is to delay or
eliminate the need for a corneal graft.
Patients with mild to moderate keratoconus appear
to be the best candidates.
Migration of rings
Extrusion or progressive thinning
New vessel formation
The gold standard surgery
Success rate is more than 90%.
In this procedure, the keratoconic cornea is
prepared by removing the central area of the cornea,
and a full-thickness corneal button is sutured in its
Usually trephines between 8.0-8.5 mm are used.
Fleischer’s ring can be used as the limit of the conical
Contact lenses are often required after this
procedure for best visual rehabilitation.
Deep Anterior Lamellar Keratoplasty
Partial corneal transplant.
The cornea is removed to the depth of posterior stroma, and the donor
button is sutured in place.
This technique is technically difficult, and visual acuity is inferior to
that obtained after penetrating keratoplasty.
As a result, use of lamellar keratoplasty is largely confined to the
treatment of large cones or keratoglobus when tectonic support is
This technique requires less recovery time, and poses less chance for
corneal graft rejection or failure.
Its disadvantages include vascularization and haziness of the graft
It involves placing a hot ring (Holmium yag laser,
2100nm) along the base of the cone to heat and
traumatize the cornea, resulting in a corneal scar which
reduces the corneal curvature.
It allows a flatter contact lens to be fitted..
The disadvantages of the procedure
o transitory corneal haze
o development of corneal scarring
Used to correct high myopia and associated
astigmatism of selected keratoconus patients.
Anterior chamber phakic intraocular lens have also
been combined with intacs with good results.
The Intacs implantation is followed by toric phakic
intraocular lens implantation to correct the residual
myopic and astigmatic refractive error.
“Five point” management algorithm for keratoconus