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COMPARE AND CONTRAST: CORNEAL REFRACTIVE SURGERIES.pptx
- 1. 1 COMPARE AND CONTRAST KERATO-REFRACTIVESURGERIES DR. FASHOLA M.B.
- 2. 2 Outline Introduction Cornea History Laser biophysics Keratorefractive surgeries Videos Comparison Conclusion
- 3. 3 Introduction Refractive surgeriesare a wide variety of surgical procedures aimed at changing the refractive status of an eye by altering the principal refractive components of the eye. The principal refractive components of the eye are the cornea and the lens. The axial length of the globe (AP diameter) also contributes to the eye’s refractive state.
- 4. 4 Introduction Refractive surgeriescan be broadly classified into corneal and lenticular procedures. Kerato-refractive surgeries (KRS) modulate the shape of the cornea to reduce refractive error, and reduce dependency on glasses and contact lenses. KRS include surface ablation procedures, “flap” or “cap” procedures, thermal procedures, incisional procedures, and surgical- addition or subtraction procedures.
- 5. 5 Introduction The eyeis a compound optical system. Incident light is focused through the cornea and lens unto the fovea. The majority of the optical power of the eye derives from the combined effect of the air–tear interface and the corneal curvature. Photocredit: Internet
- 6. 6 Cornea The corneais a transparent avascular tissue, it contributes to 2/3rd of the refractive power of the eye. It has five distinct layers. There is an increase in thickness from central to the periphery, the CCT ranges from 551-565μ and the PCT from 612-640μ. Photocredit: Internet
- 7. 7 Cornea It isconvex and aspheric (Prolate). It measures 11–12 mm horizontally and 9–11 mm vertically. The anterior curvature is about 7.8 mm and posterior curvature is about 6.5 mm. Refractive power (about 42D) Anterior curvature is about +48D Posterior curvature is about -6D Photocredit: Internet
- 8. 8 History Year Ophthalmologist Procedure 1898Dr. Lans (Netherlands) Basic principles of Radial keratotomy laid up 1930 Tsutomu Sato (Japan) Pioneering work on corneal incisions 1948 Jose Barraquer (Colombia) First corneal reshaping surgery (freezing a flap of cornea, reshaping it & placing it back 1960s Fyodorov et al (Russia) Radial Keratotomy 1975 Anthony Gasset et al Thermokeratoplasty 1978 Leo Bores (US) Radial keratotomy 1975- 1979 Srinavasan (USA IBM Labs) Excimer laser developed
- 9. 9 Year Ophthalmologist Procedure 1983Stephen Trokel (USA) Excimer laser modified for ophthalmic use 1988 Theo Seiler (Germany) First excimer treatment on human eye 1989 Pallikaris (Greece) & Buratto (Italy) Experimentation with PRK 1995 FDA approves excimer laser for PRK for myopia 1999 First excimer laser approved for LASIK 1999 Massimo Camellin (Italy) LASEK introduced 2000 FDA approves LASIK for hypermetropia 2002 Wavefront-guided LASIK approved History
- 10. 10 Year Ophthalmologist Procedure 2002First Femtosecond laser flap removal approved by FDA 2003 Pallikaris (Greece) First EpiLASIK procedures performed History
- 11. 11 Laser biophysics Photoablation:Electrical energy stimulates argon to form dimers with fluorine (excimer), producing 93nm UV light, which produces high precision breakage of intermolecular bonds that vaporizes and reshapes tissue surface. Photocredit: Internet
- 12. 12 Laser biophysics Photodisruption(Femtosecond laser): Infrared light (1,053nm) generates very localized high temperatures, which causes rapid tissue expansion, and small cavitation bubbles that allow tissue separation. Photothermal (Holmium laser): Holmium:YAG laser is absorbed by water in the cornea causing thermal collagen shrinkage. Photocredit: Internet
- 13. 13 Laser biophysics Conventionaltreatment Conventional is the standard laser vision correction surgery. It corrects lower order abberations (myopia, hypermetropia, astrigmatism) using a fixed treatment pattern. It does not account for individual variations in eye imperfections, and cannot be used for higher order aberrations (coma, trefoil etc). Results can be good, but it lacks the precision of customized laser.
- 14. 14 Laser biophysics Wavefront-guided treatment This uses advanced wavefront technology to create a detailed map of each eye and it’s unique imperfections. This map guides the laser, and can correct higher-order aberrations, providing more personalized treatment. It improve visual quality and reduce glare and halos seen with conventional treatment.
- 15. 15 Laser biophysics Wavefront-optimized treatment It combines conventional measurements with wavefront data. It maintains the natural curvature of the cornea while correcting refractive errors. This approach minimizes induced aberrations and provides good visual outcomes. It’s suitable for patients with lower-order aberrations and regular corneas
- 16. 16 Laser biophysics Topography-guided treatment (Contoura® Vision) Contoura® Vision is an FDA-approved topography-guided LASIK. It uses detailed corneal topography maps to customize treatment. By addressing both refractive errors and corneal irregularities, it achieves superior visual quality. Contoura® Vision is considered the most advanced LASIK technology in the U.S.
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- 18. 18 Laser ablation profile Photocredit:Oxford handbook
- 19. 19 Keratorefractive surgeries Surface ablation procedures Flapor cap procedures Incisional procedures Addition/ Subtraction procedures Thermal procedures Photorefractive keratectomy (PRK) Laser in-situ keratomileusis (LASIK) Radial keratotomy (RK) Intracorneal ring segments Laser thermal keratoplasty (LTK) Laser subepithelial keratomileusis (LASEK) Arcuate keratotomy (AK) Corneal inlays Conductive keratoplasty (CK) Epithelial laser in- situ keratomileusis (EpiLASIK) Limbal relaxing incisions (LRI) Small incision lenticule extraction (SMILE), FLeX, ReLeX `
- 20. 20 Photorefractive Keratectomy Procedure:PRK is an outpatient surgery and takes approximately 5-15 minutes per eye to complete. Anesthetic drops instilled and speculum to expose cornea Patient focuses on a target light Corneal epithelium removed (Mechanical, Chemical, Laser) Laser applied to bowman layer and anterior stroma for up to 30- 60secs. CL is inserted until epithelial defect healed.
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- 22. 22 Laser-assisted in-situ keratomileusis(LASIK) Procedure: Topical anesthetic is instilled. Suction ring applied (raises IOP to 60mmHg) Flap containing epithelium, Bowman’s layer and superficial stroma is raised, with hinge superiorly or nasally. Excimer laser applied to stroma for up to 30-60secs. Flap is re-positioned.
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- 24. 24 Laser-assisted Subepithelial Keratectomileusis (LASEK) A "hybrid" technique between LASIK and PRK. Procedure: 20% Ethanol is applied for 30-40secs to cleave the epithelium at the basement membrane. Epithelium is rolled back as a sheet, laser is applied, epithelium is re- positioned. Bandage contact lens (BCL) is applied, as for PRK. Photocredit: Internet
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- 26. 26 Epithelial Laser in-situkeratomileusis (EpiLASIK) Procedure: An Epi-keratome is used to precisely separate a very thin sheet of corneal epithelium. This thin sheet is lifted to the side and the cornea is treated as with PRK. Then the thin sheet is moved back into place to re-adhere to the cornea. A BCL is applied.
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- 28. 28 Complications Error inprogramming Incomplete epithelium removal Decentered ablation Epithelium or Flap button hole Flap amputation Intra-operative
- 29. 29 Complications: Post-operative Photophobia Pain Glare, Haloes Corneal haze Undercorrection Overcorrection Infection Corneal striae or folds Dry eye Corneal ectasia Induced aberrations from small optical zones Flap (epithelial ingrowth, dislocation)
- 30. 30 Complications Infectious keratitis Persistent epithelial defects Steroid-induced complications Diffuse lamellar keratitis
- 31. 31 Aspect PRK LASEKEpiLASIK LASIK Indications Myopia up to -12D Hyperopia up to 6D Astigmatism up to 5D Myopia up to -12D Hyperopia up to 6D Astigmatism up to 5D Myopia up to - 12D Hyperopia up to 6D Astigmatism up to 5D Myopia up to -12D Hyperopia up to 6D Astigmatism up to 5D Type Surface ablation Surface ablation Surface ablation Flap procedure Procedure Removes the epithelial layer of cornea Creates a sheet of epithelium + replacement Creates a flap of epithelium + replacement Creates a flap (epithelium, Bowmans membrane and superficial stroma)
- 32. 32 Aspect PRK LASEKEpiLASIK LASIK Recovery Time Longer recovery time Faster than PRK, Longer than EpiLASIK & LASIK Faster than PRK & LASEK, Longer than LASIK Faster recovery Cornea Thickness Suitable for thin corneas Suitable for thin corneas Suitable for thin corneas Requires thicker corneas Post-op pain Most discomfort More discomfort Less discomfort Least discomfort Risk of Haze Highest risk High risk High risk Slightly lower risk Dry Eyes Less impact on tear production. Less impact on tear production. Less impact on tear production. Causes dry eye Sport & activities Preferred for contact sports Same as PRK Same as PRK Not suitable for contact sports
- 33. 33 Aspect PRK LASEKEpiLASIK LASIK Medication Period Longer medication period Longer medication period Longer medication period Shorter medication period Visual Recovery Slower visual recovery Similar to PRK Similar to PRK Improvement within a day or two General complications risk Slightly higher risk Slightly higher risk Slightly higher risk Slightly lower risk Flap complication risk No risk No risk Minimal risk Highest risk Night Vision Potential for poor night vision Potential for poor night vision Potential for poor night vision Good night vision
- 34. 34 Small Incision LenticuleExtraction (SMILE) The procedure involves removal of a lenticule of tissue from the corneal stroma. It represents the newest laser refractive procedure. Indications: myopia up to −10.00D. Astigmatism up to 5.00D. Not used for hypermetropia yet.
- 35. 35 SMILE Method: Anintrastromal lenticule is created using FSL. A small surface incision (2– 4mm wide) is then created using the FSL which is continuous with the lenticule. The lenticule of tissue is then removed via the surface channel through surgical instrumentation. There is no flap.
- 36. 36 SMILE Advantages: Lesspainful than surface ablations. Rapid visual rehabilitation, Less dry eye and quicker recovery from dry eye. Compared to LASIK, allows treatment of thinner corneas. Disadvantages: Unsuitable for hypermetropia Relatively new, long- term results not available, available data encouraging.
- 37. 37 Conclusion Keratorefractive surgeriesoffer effective and precise options for the correction of refractive errors. From PRK to LASIK to SMILE, each technique has its unique advantages and disadvantages, it is essential to consider individual patients needs, anatomical characteristics, and visual goals to determine best option.
- 38. 38 References J. Kanski,Clinical Ophthalmology; A systematic approach; 9th edition; p 245-249 A.K.O. Denniston, P.I. Murray, Oxford Handbook of Ophthalmology, 4th edition; p 946-973 American Academy of Ophthalmology Basic Clinical Science Course, Section 13: Refractive Surgery, 2023-2024 Eyewiki AAO.org Sciencedirect
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