the preparations to make in accessing whether a patient is fit for surgery

1. PATIENT HISTORY,EXAMINATION AND
ANCILLARY TESTS
PRESENTER:DR.MUGABI BARNABAS
MODERATOR: DR.SSALI

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

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

13. • Pterygium surgery
• Glaucoma and Previous Glaucoma Surgery
• 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
• Visual acuity- BCVA, UCVA
• Clinical Refraction- Manifest and cycloplegic refraction
• Pupillometry
• Tear film tests
• IOP measurements
• Ocular motility
• Orbital anatomy

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

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

21. Corneal imaging

22. 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.

45. Enantiomorphism

46. 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.

49. • 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.
• Determination of morphologic patterns of the cone in ectatic corneal
disorders

50. • Depending on this map, there are three patterns of the cone:
• a. Nipple
• b. Oval
• c. Globus

54. 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.

56. 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

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

60. Types of RS
• Best fit sphere (BFS)
• Best fit ellipsoid (BFE)
• Best fit toric ellipsoid (BFTE)

61. Best fit sphere

68. CONE LOCATION

69. 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

75. 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

77. Principle

80. 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

81. 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

82. 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.

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

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

94. • 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

95. Wavefront science

96. 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

97. Refractive Error: Optical Principles and
Wavefront Analysis
• Measures lower-order aberrations (sphere and cylinder) and higher-
order aberrations (spherical aberration, coma, trefoil).
• Used in calculating custom ablations to enhance vision.

98. Hartmann-Shack

99. Hartmann-Shack
• 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

100. Hartmann-Shack
• 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

107. • Defocus

108. • Astigmatic aberration

110. 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

112. Spherical aberration

113. Trefoil

114. • 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

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