Download to read offline
More Related Content
Similar to REFRACTIVE SURGERY PRESENTATION.pptx
More from BARNABASMUGABI
REFRACTIVE SURGERY PRESENTATION.pptx
- 1. PATIENT HISTORY,EXAMINATION AND ANCILLARYTESTS PRESENTER:DR.MUGABI BARNABAS MODERATOR: DR.SSALI
- 2. • The goalof 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.
- 4. Psychosocial approach • Patientswith 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 • Onsetof refractive error • Stability • Anisometropia • Age and presyopia
- 8. Use of ContactLens • 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 andInfection • 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 • Pathologicalfindings such as retinal tears or atrophy or optic nerve head atrophy • Corneal opacities and scars • Iridodenesis • Lens subluxation
- 12. Previous Surgeries • Refractivesurgery • 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- predisposeto 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 • Cardiacpacemakers 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 • Apositive 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 Slitlamp examination • Blepharitis and meibomitis • Keratitis and punctate keratopathy, scarring, dystrophies • Conjunctival scars, bleb, buckle • Cataract
- 20. Fundoscopy • Peripheral retinalpathology • Diabetic retinopathy • Macular edema, epiretinal membranes and degenerative changes in the macula • ONH abnormality
- 21.
- 22. Topography and tomographysciences • 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.
- 46. Instantaneous power andcurvature • 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 mapsare 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 onthis map, there are three patterns of the cone: • a. Nipple • b. Oval • c. Globus
- 54. Elevation maps • Elevationmaps 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 thereference 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- meancentral 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.
- 68.
- 69. PACHYMETRY MAPS • Thereare 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.
- 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 • Cornealthickness 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 • Measuresthe slope of the cornea • Affected by keratorefractive surgery • Abnormal corneal topometry is the main cause of spherical aberrations
- 89. • Corneal surfacemay take one of four main shapes: • Spheric • Aspheric oblate • Aspheric prolate • Aspheric hyperprolate
- 94. • Corneal topometryis 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.
- 96. Refractive Error: OpticalPrinciples 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: OpticalPrinciples 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.
- 99. Hartmann-Shack • In anaberration-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 extentof 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.
- 107.
- 108.
- 110. Higher-Order Aberrations • Mayor 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.
- 113.
- 114. • HOAs cannotbe 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-orderaberrations • There are numerous other higher-order aberrations, of which only a small number are of clinical interest