The document discusses various aspects of patient evaluation and treatment options for refractive surgery. It describes evaluating a patient's psychosocial factors, medical and ocular history, and examination findings to determine suitability for different refractive surgery techniques. A variety of surgical options are outlined including corneal procedures like LASIK, PRK, and lens-based procedures. Topics like wavefront analysis and assessing higher-order aberrations are also summarized.

1. REFRACTIVE
SURGERIES
-Shreya

2.  The goal of refractive surgery is to reduce
dependence on contact lenses or glasses for
use in routine daily activities.
 A wide variety of surgical techniques and
technologies are available, and all require an
appropriate preoperative evaluation to
determine the best technique and ensure the
optimal outcome for each patient individually.

3. PATIENT EVALUATION

4. Psychosocial approach
 Patients with unreasonable high expectations and
those with type-A and compulsive personalities
are not good candidates for refractive surgery
 A good candidate is that who understands that the
refractive surgery is not risk-free, follows
instructions, is willing to wear glasses after the
surgery
 A good surgeon is that who does not give unreal
promises, tells that patient the reasonable
expected visual acuity and visual function and
discusses the issue of enhancement.

5. Social History
 Profession
 Patient expectations
 Suitability for post-operative care

6. Ocular history
 Refractive
 Use of Contact Lens
 Dry Eye Syndrome (DES)
 Chronic Allergy and Infection
 Ocular trauma
 Previous Surgeries

7. Refractive history
 Onset of refractive error
 Stability
 Anisometropia
 Age and presyopia

8. Use of Contact Lens
 Type
 Wearing schedule
 Type of cleaning solution, cleaning practices
Using CLs should be stopped 2–4 weeks prior to
examination:
 Alters the topographic features of corneal
surface
 Cause of apparent irregular astigmatism
 Changes the amount, type and axis of
astigmatism
 Can alter corneal thickness

9. Dry Eye Syndrome (DES)
 Stability of the tear film-Tear film break-up time
(TBUT)
 Tear production- Schirmer, flourescein
clearance
 Ocular surface disease- Corneal stains and
impression cytology
 Tarsal transillumination to visualize the
meibomian glands

10. Chronic Allergy and Infection
 Constant rubbing and development of
keratoconus.
 Constant rubbing and post LASIK
complications such as flap dislocation.
 Chronic infections and post surgery
complications

11. Ocular trauma
 Pathological findings such as retinal tears or
atrophy or optic nerve head atrophy
 Corneal opacities and scars
 Iridodenesis
 Lens subluxation

12. Previous Surgeries
 Refractive surgery
 Cataract surgery- IOL, technique, date of
surgery
 Retinal surgery
 Squint surgery
 Pterygium surgery
 Glaucoma and Previous Glaucoma Surgery

13.  Keratoconus and ectatic Corneal Disorders
Other Pathologies-
 Recurrent corneal erosion, corneal ulceration
or ocular infections

14. General history
 Diabetes
 Hypertension
 Allergy and Atopic Disease
 Collagen Vascular Diseases and Inflammatory
Disorders
 Keloid Formation Diseases
 Pregnancy and Nursing
 Immunodeficiency

15. Medications
 Anticoagulants- predispose to conjunctival
hemorrhage or expulsive choroidal hemorrhage
during intraocular refractive surgery
 Isotrentoin, Amiodarone, hormone replacement
therapy and antihistamines- delays corneal
epithelial healing
 Immunosuppressants and high dose systemic
steroids- predispose to infections.
 5-Hydroxy-tryptamine (Sumatriptan)- increased
risk of vascular occlusion when IOP is raised
during application of suction ring.

16. Other Conditions
 Cardiac pacemakers and implanted
defibrillators, due to the unknown effects of the
laser’s electromagnetic emissions.
 Epilepsy: patients that have not had an
epileptic episode for twelve months or more
may be considered for treatment.
 History of frequent fainting: low threshold for
vasovagal attack.
 Hepatitis B and C: potential risk to surgical
staff

17. Family History
 A positive history of any of the followings warrants
further careful ocular evaluation prior to surgical
intervention:
 KC and ectatic corneal disorders.
 Glaucoma.
 Past history of high intraocular pressure after
topical steroid application.
 Corneal dystrophy or degeneration.
 Retinal pathology (e.g. retinal holes, tears, or
detachment)

18. Examination

19. Examination
 Visual acuity- BCVA, UCVA
 Clinical Refraction- Manifest and cycloplegic
refraction
 Pupillometry
 Tear film tests
 IOP measurements
 Ocular motility
 Orbital anatomy

20. External and Slit lamp
examination
 Blepharitis and meibomitis
 Keratitis and punctate keratopathy, scarring,
dystrophies
 Conjunctival scars, bleb, buckle
 Cataract

21. Fundoscopy
 Peripheral retinal pathology
 Diabetic retinopathy
 Macular edema, epiretinal membranes and
degenerative changes in the macula
 ONH abnormality

22. Corneal imaging

23. Topography and tomography
sciences
 Corneal topography- Placido-based machines consisting
of two maps: anterior sagittal (axial) and anterior
tangential (instantaneous) curvature maps.
 Corneal tomography-
 maps and images given by Scheimpflug-based machines
 topographic maps with more maps and profiles of both
corneal surfaces and corneal pachymetry map.
 most important screening test for refractive surgery to
detect abnormalities, diagnose early cases of ectatic
corneal diseases and classify these diseases, diagnose
post keratorefractive ectasia and put the plan for the best
choice in refractive surgery.

46. Enantiomorphism

47. Instantaneous power and
curvature
 Also called meridional or tangential power
 Better sensitivity to peripheral changes
 less “smoothing” of the curvature
 In these maps, diopters are relative units of
curvature and are not the equivalent of
diopters of corneal power.

50.  Tangential maps are more susceptible to local
curvature changes, because it depends on
circles
 Each point on the tangential map is
independent of any reference axis- less
affected by misalignments.

51.  Determination of morphologic patterns of the
cone in ectatic corneal disorders
 Depending on this map, there are three
patterns of the cone:
 a. Nipple
 b. Oval
 c. Globus

55. Elevation maps
 Elevation maps describe the height details of
the measured corneal surface by matching it
with a reference surface(RS) above which
points are considered elevations and expressed
in plus values and below which points are
considered depressions and expressed in
minus values.

57. Position of the reference sphere
 Float mode - RS is adjusted with the corneal
surface such that all elevations are equal to all
depressions.
 Non-float mode – RS touches the apex of
cornea

59. Parameters
 Radius- mean central radii of measured
corneal surface
 Diameter - diameter of the used zone of the
cornea

61. Types of RS
 Best fit sphere (BFS)
 Best fit ellipsoid (BFE)
 Best fit toric ellipsoid (BFTE)

62. Best fit sphere

69. CONE LOCATION

70. PACHYMETRY MAPS
There are three main land marks on the
pachymetry map:
 cornea apex
 thinnest location
 two opposing points on the vertical meridian at
the central 5 mm circle
The two opposing points are superior (S) and
inferior (I); the normal S-I difference is <30
microns

76. Belin/Ambrosio enhanced
ectasia
 Elevation based classification system for early
detection of ectatic corneal diseases (ECDs).
 Principle of ‘enhanced best fit sphere’ (BFS)
1. Belin/Ambrosio ectasia display (BAD)
2. Pachymetric data
3. Numeric values

78. Principle

81. Progression index
 Min- Pachymetric progression index minimum
Half meridian with smallest progression index.
(green)
 Max- Pachymetric progression index maximum
Half meridian with largest progression index. (blue)
 Avg- Pachymetric progression index average
Ratio of individual progression to normative
progression.
 ARTmax- Ambrosio Relational Thickness
maximum
Ratio of thinnest corneal thickness to pachymetric

82. Deviation parameters
 Df- deviation of front elevation difference map
 Db- deviation of back elevation difference map
 Dp- deviation of average pacymetric
progression
 Dt- deviation of minimum thickness
 Da- deviation of ARTmax
 D- total deviation value

83. Pachymetry profiles
 Corneal thickness spatial profile (CTSP)
describes the average progression of
thickness starting from the thinnest location to
corneal periphery in relation to zones
concentric with the thinnest location.
 Percentage thickness increase (PTI) describes
the percentage of progression of the same.

89. Corneal topometry
 Measures the slope of the cornea
 Affected by keratorefractive surgery
 Abnormal corneal topometry is the main cause
of spherical aberrations

90. Corneal surface may take one of four main
shapes:
 Spheric
 Aspheric oblate
 Aspheric prolate
 Aspheric hyperprolate.

96.  Corneal topometry is expressed by Q-value
 Normal Q-value is –1 to 0
 Q-value is positive (>0) in oblate cornea
 Q-value is negative (<-1) in prolate and
hyperprolate cornea
 Q-value is plano (=0) in spherical cornea
 Abnormal Q-value results in spherical
aberrations

97. Wavefront science

98. Refractive Error: Optical Principles
and Wavefront Analysis
 One of the major applications of the wave theory of
light is in wavefront analysis.
 Currently, wavefront analysis can be performed
clinically by 4 methods:
1. Hartmann-Shack
2. Tscherning
3. Thin-beam single-ray tracing
4. Optical path difference
 Measures lower-order aberrations (sphere and
cylinder) and higher-order aberrations (spherical
aberration, coma, trefoil).
 Used in calculating custom ablations to enhance
vision.

99. Hartmann-Shack

100.  In an aberration-free eye, all the rays would emerge in
parallel, and the reflected wavefront would be a flat
plane (piston).
 In reality, the wavefront is not flat.
 To determine the shape of the reflected wavefront, an
array of lenses samples parts of the wavefront and
focuses light on a detector
 The extent of the divergence of the lenslet images from
their expected focal points determines the wavefront
error.
 Optical aberrations measured by the aberrometer can
be resolved into a variety of basic shapes, the
combination of which represents the total aberration of
the patient’s ocular system.

104. Low order aberrations
 Low order aberrations (LOAs) are aberrations
associated with the spherocylindrical refractive
errors.
 Can be corrected with glasses.
 LOAs constitute 85% of aberrations
 There are three types of LOAs- tilt, defocus
and astigmatic aberrations.

105. Tilt

106. Defocus

107. Astigmatic aberration

109. Higher-Order Aberrations
 May or may not be associated with refractive
errors
 HOAs result from media irregularities or
opacities
 Although there is a wide range and types of
HOAs, the main types are coma, trefoil and
spherical aberrations
 HOAs impact vision more severe than LOAs
 Coma is a central aberration and affects
central vision, whereas trefoils and spherical
are peripheral aberrations

111. Spherical aberration

112. Trefoil

113.  HOAs cannot be corrected with classic optics
 Coma results from a variation of magnification
(refractive power) over the entrance pupil. It
affects central vision
 Trefoil aberration results from regular
alternating variation in magnification along the
meridians in corneal periphery. It affects
peripheral vision.
 Spherical aberration results from abnormal Q
value. It affects peripheral vision

114.  Other higher-order aberrations
 There are numerous other higher-order
aberrations, of which only a small number
are of clinical interest.

115. Measurement metrics
 Objective visual function is measured at
corneal level (corneal wavefront) and at
pupillary level (ocular wavefront) by root mean
square method (RMS)
 Deviation averaged over the entire wavefront
in reference to the perfect wavefront.
 Quantitative value
 For large deviations
 Normal emmetropic eyes- ≤0.4µm.

116. RMS= √(+0.25)2+(-0.40)2+(+0.30)2
=0.559µm

117. Types of refractive surgeries

118. Types
 Corneal
 Intraocular

119. Corneal
 Incisional
 Excimer laser
 Non laser lamellar
 Collagen shrinkage
 Collagen cross linking

120. Corneal- incisional
 Radial keratotomy RK- (historical)
 Astigmatic keratotomy-
1. Arcuate keratotomy AK
2. Femto laser assisted arcuate keratotomy
FLAAK
3. Limbal relaxing incision LRI

121. Cornea- Excimer laser
Surface ablation
 Photorefractive keratectomy- PRK
 Laser subepithelial keratomileusis LASEK
 Epipolis lasik
Lamellar
 LASIK
 Femto LASIK
 Refractive lenticule SMILE

122. Photo refractive treatment
 Surface Ablation (SA)
 Bowman layer and anterior stroma.
 Photorefractive Keratectomy (PRK): The
epithelium is debrided and removed either
mechanically or by 20% alcohol
 Laser Subepithelial Keratomileusis (LASEK):
The epithelium is loosened by 20% alcohol
and moved aside, but ultimately preserved,
then re-positioned after ablation

123.  Epipolis LASIK (Epi-LASIK): The epithelium is
moved mechanically by a mechanical
microkeratome (MMK), but ultimately
preserved, then re-positioned after ablation
 Transepithelial Photorefractive Keratectomy
(TE-PRK): The epithelium is not removed but
ablated with a specific profile designed to
remove the epithelium and simultaneously
correct the refractive error

124. Diagrammatic comparison of single and multizone
keratectomies.
A. Depth of ablation required to correct 12.00 D of myopia
in a single pass.
B. Depiction of how the use of multiple zones reduces the

125. Lamellar Ablation (LA)
 Photoablation is performed on anterior stroma
under a lamellar flap created with either a
MMK or femtosecond laser
 The lamellar type is called laser in situ
keratomileusis (LASIK).

126. Surface-Lamellar Ablation
(SLA)
 Photoablation is performed just sub Bowman
layer under a very thin lamellar flap created
with either a MMK or femtosecond laser,
therefore, it is called sub Bowman
keratomileusis (SBK).

127. SMILE
 Small incision lenticule extraction

128. Cornea- Non laser lamellar
 Epikeratophakia (historical)
 Epikeratoplasty (historical)
 Intra stromal corneal ring segments
-keratoconus
-Post LASIK ectasia

130. Collagen Shrinkage Techniques
 Alteration in corneal biomechanics can also be
achieved by collagen shrinkage.
 Heating collagen to a critical temperature of
58°–76°C causes it to shrink, inducing
changes in the corneal curvature.
 Thermokeratoplasty and conductive
keratoplasty (CK) are avoided in the central
cornea because of scarring but can be used in
the midperiphery to cause local collagen
contraction with concurrent central corneal
steepening

131. Collagen shrinkage
 Laser thermokeratoplasty
 Conductive keratoplasty
Corneal collagen cross linking

132. Conductive keratoplasty

133. Intra ocular
 Phakic
 Pseudophakic

134. Phakic IOLs
 Phakic IOLs (PIOLs) are additive lenses
implanted into the anterior or posterior
chambers of the eye to compensate for
refractive errors and at the same time
preserving the crystalline lens and
accommodation

135.  Three types of PIOLs are currently available:
 1. Angle-Supported (anterior chamber)
 2. Iris-Fixated (anterior chamber)
 3. Sulcus-Supported (posterior chamber)
 The power of a phakic lens is independent of
the axial length of the eye. Rather, it depends
on central corneal power (K-readings), ACD
and patient refraction.

136. Indications
 PIOLs are usually indicated where
photoablation is relatively or absolutely
contraindicated.
 PIOLs are implanted in case of:
 1. High refractive errors
 2. Thin corneas.
 3. Abnormal (suspicious) corneal tomography.
 4. Dry eye.

137. Refractive lens exchange (RLE)
 Refractive lens exchange (RLE) is extracting
the clear crystalline lens and implantation of
an IOL to compensate for refractive errors
 It can be considered as one of the refractive
options to treat refractive errors, but has very
limited indications and carries almost the same
risks of cataract extraction

138.  Monofocal IOL
 Toric IOL
 Multifocal IOL
 Accomodating IOL

139. THANK YOU!