LASIK.pptx

LASIK or Lasik (laser-assisted in situ keratomileusis), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, since it is in the cornea. LASIK surgery is performed by an ophthalmologist who uses a laser or microkeratome to reshape the eye's cornea in order to improve visual acuity. For most people, LASIK provides a long-lasting alternative to eyeglasses or contact lenses.
The planning and analysis of corneal reshaping techniques such as LASIK have been standardized by the American National Standards Institute, an approach based on the Alpins method of astigmatism analysis. The FDA website on LASIK states,

"Before undergoing a refractive procedure, you should carefully weigh the risks and benefits based on your own personal value system, and try to avoid being influenced by friends that have had the procedure or doctors encouraging you to do so."

The procedure involves creating a thin flap on the eye, folding it to enable remodeling of the tissue beneath with a laser and repositioning the flap.

1. LASIK (Laser Assisted In Situ Keratomileusis) - Surg Lt Cdr (Dr) Prabhjot Singh AFMC, Pune

2. REFERENCES Cornea by Jay H Krachmer MD- 3rd Ed Refractive Surgery- AAO Ophthalmology- Myron Yanoff, MD

3. Previous questions LASIK – Principle, advantages and disadvantages. Summer 2009,2012 Describe recent advances in laser refractive surgery. Winter 2016 Describe recent advances in keratorefractive surgeries. Winter 2010 Femtosecond laser in cataract and refractive surgery- Principle, technique, advantages and disadvantages. Summer 2015 Excimer laser- Indications. Summer 2010 Femtolaser. Summer 2013, Winter 2010,2014,2015 IOL power calculation. Describe IOL power calculation in post refractive surgery patients. Summer 2018, Winter 2016

4. The Science of Refractive Surgeries Reduces dependence on contact lenses or spectacles Appropriate preoperative evaluation to determine the best technique

5. LASIK(Laser Assisted In Situ Keratomileusis) Greek words for “cornea” (kerato) and “to carve” (mileusis). combines lamellar corneal surgery with the accuracy of the excimer laser. Involves excimer laser ablation of corneal stroma beneath a hinged corneal flap that is created with a microkeratome or a femtosecond laser most frequently performed keratorefractive procedure because of its safety, efficacy, quick recovery of vision, and minimal patient discomfort.

6. Excimer Laser Excited dimer of Argon and Fluoride - releases UV energy at 193nm for corneal ablation photoablates or vaporizes tissue by breaking intramolecular bonds and generating unstable smaller particles. The 193 nm wavelength - optimal for surgical use shorter wavelength lasers - technically difficult to produce longer wavelength lasers (200 nm and above)- produce undesirable thermal effects MOA- Non thermal Ablative photodecomposition

7. Patient selection >18 years Stable Refractive status for at least 1 year. Current FDA approval- Myopia upto -12D Hyperopia upto +6D Astigmatism upto 6D however the results have been better in lower ranges than in higher ranges of correction. Most surgeons limit levels of correction to less than 8.00–10.00 D of myopia and 4.00 D of hyperopia

8. CCT such that minimum safe bed thickness left (250-270µ). Post op Corneal thickness should not be <410µ. Cornea not too flat or steep <36D or >49D

9. CONTRAINDICATIONS Systemic factors- Poorly controlled IDDM Pregnancy/lactation Autoimmune / connective tissue disorders (RA,SLE,PAN etc) Clinically significant Atopy, Immunosuppressed patients Keloid tendency Slow wound healing- Marfans,Ehler-Danlos Systemic Infection-(HIV,TB) Drugs-Azathioprene,Steroids(Slow wound healing)

10. CONTRAINDICATIONS Ocular Factors- Glaucoma, RP (Suction Pressure-ON damage, Blebs) Previous h/o RD One eyed Pre-existing dry eye, Keratoconus, pellucid marginal degeneration, Superficial corneal dystrophy, Uveitis, early Lenticular changes h/o Herpetic Keratitis (one year prior to surgery)

11. PREOPERATIVE EVALUATION PRIOR TO LASIK UCVA and BCVA Dry and wet manifest refraction (with 1% cyclopentolate) Pupillometry Large pupil - increased glare - Can change Optic Zone Slit Lamp Examination- Rule out blepharitis, miebomianitis, pingecula, Pterygium, corneal neovascularization Other contraindications for LASIK. IOP by applanation Dilated Fundus Examination

12. Tear film asessment- Schirmers, TBUT and Lissamine staining Blink Rate-(Normal---3-7/min) Corneal Topography- Stop RGP lenses 2 weeks prior and soft lenses I wk prior To rule out early Keratoconus and other ectasias For mean K values Pachymetry -For CCT Contrast Sensitivity testing for pre-operative baseline.

13. OPERATIVE TECHNIQUE Suctiion ring Flap Creation Excimer lase ablation Flap Repositioning

14. BASIC STEPS AND MACHINE SPECIFICATIONS Topical anasthesia Surgical Painting and draping Lid speculum with aspiration. Corneal marked with two circular markings of 3.0 mm and 3.5 mm, marked with gentian violet and applied peripherally and inferiorly before creating the corneal flap with the microkeratome to more easily realign the corneal flap in the event that a free flap is created. In addition, the two circles of different sizes provide four-point alignment that will prevent any chance of the flap being placed epithelial-side down.

15. Application of the pneumatic suction ring lid speculum is depressed to proptose the eye to allow better apposition of the ring to the globe suction ring is then placed on the eye Patient is warned of a slight feeling of pressure and discomfort. The suction ring is firmly and steadily depressed downward , while the ring is twisted slightly in clockwise and counterclockwise fashion in order to securely seat and seal the ring.

16. If the position is adequate, the suction pressure is activated and the patient is warned that the fixation and other lights may go out completely and that vision will go dark. At this point, four helpful signs assure the surgeon that adequate suction has been obtained: 1. The suction ring can be lifted toward the ceiling slightly and the eye should come up with it. 2. The pupil will dilate slightly. 3. The patient will confirm that everything has gone dark. 4. The eye will feel firm to palpation.

17. Checking for adequate intraocular pressure Raise the IOP to 65 mm Hg which is necessary for the microkeratome to create a pass and resect the corneal flap. This is crosschecked with Barraquers tonometer.

18. Insertion of the microkeratome head and creation of the keratectomy Adequate lubrication Resection of corneal flap Several different microkeratomes are available Microkeratome Femtosecond Laser (Intralase)

19. Microkeratome Uses Disposable blades If using a two-piece microkeratome, the head is slid onto the the suction ring and advanced until the gear on the microkeratome head engages the track. The surgeon then activates the microkeratome using forward and reverse foot control, the suction is turned off after the microkeratome pass, and then the suction ring can be carefully removed.

20. Femtosecond Laser for Flap uses laser pulses to cause microcavitation bubbles at a preset depth in the corneal stroma The cavitation bubble is composed primarily of water and carbon dioxide. Multiple cavitation bubbles coalesce, and an intrastromal cleavage plane is created

21. Creates photodisruption using femtosecond solid state laser with wavelength of 1053nm. Needs lower vacum. Very short pulse with spot size of 3µ High precision cutting device. Any hinge can be made Can make flaps as thin as 100µ (Sub BowmannsKeratomileusis) Better LASIK outcomes

22. Typically, an applanation cone with an optical glass lens flattens the cornea and maintains a precise distance from the laser head to the focal point, while a suction ring provides a docking port on the eye for the applanation cone

23. Femtosecond laser advantages reduced patient anxiety. deep-set or small eyes, blepharospasm, or steep or flat corneas more control over flap centration, size, hinge location, and hinge width Femtosecond incisions can also be used for lamellar keratoplasty, penetrating keratoplasty, intrastromal corneal ring channels Potential disadvantages include increased procedure time and expense, possible residual adhesions cavitation bubble migration into the anterior chamber and resulting interference with excimer ablation, and postoperative transient light sensitivity syndrome (TLSS).

24. Lifting of the corneal flap and preparation of the stromal bed Flap is reflected back with either a blunt, fine tying forceps or a cyclodialysis spatula Some surgeons reflect the flap back so that the stromal surfaces are opposed and the epithelial surface is exposed in a ‘taco’ fashion

25. Once the flap is reflected- stromal bed carefully inspected for any irregularities A Microsurgical sponge is then used to removed excess fluid from the bed and obtain uniform hydration. Nonuniform hydration would influence refractive predictability Assessment of the thickness of the residual corneal bed may be performed by using ultrasound pachymetry

26. Intrastromal ablation After flap is lifted, laser is applied to the stroma according to the ablation profile calculated by the machine. Laser beam is delivered by the following ways depending on the machine- Beam Delivery Broad Beam Scanning Slit Beam Flying Spot

27. Most machines employ a flying spot to deliver laser with the help of incorporated eye tracker. The laser eye tracker and iris registration are activated, and the laser ablation initiated

28. Reapproximation of the corneal flap After irrigating interface ,flap reposited Sweeping movements should be performed from the hinge toward the periphery of the flap.

29. Flap alignment Ends of the previously placed alignment marks carefully reapproximated. Keratectomy gutter checked along its entire circumference to ensure that the space between the edge of the flap and the peripheral cornea is the same throughout If Misaligned- refloat the flap to attain better approximation. A flap compressor can also be used to smooth wrinkles by compressing the cornea centrally Small misalignments can be easily managed by using a partially moistened expanded microsurgical sponge to manipulate the flap into the proper position

30. Adequate adhesion Wait for several minutes - allows for adequate adhesion methods to ensure firm flap adhesion . Striae test - irrigating cannula or spatula is used to depress the peripheral cornea adjacent to the edge of the keratectomy. The presence of striae in the flap indicates adequate adhesion. Blink test -have the patient blink several times while observing the flap - if no movement- adhered

31. POSTOPERATIVE CARE Topical prophylactic antibiotics and corticosteroids QID for 1–2 weeks. Preservative-free lubricating drop POD-1 , careful evaluation of the corneal flap may resume most activities

32. LASIK for Myopia The normal cornea has a prolate shape (greater curvature centrally than peripherally LASIK for myopia reverse this prolate cornea and decrease the central corneal curvature to create an oblate shape different for hyperopia - ablation is directed toward the periphery of the underlying stroma with minimal ablation occurring at the center of the cornea.

33. LASIK for Hypermetropia More than 4 -5 D - major challenge to the refractive surgeon Consider the age of the patient in surgery for hyperopia must consider manifest, latent, and facultative hyperopia in planning surgery and to anticipate the long-term efficacy of the procedure It is common for a young patient to have latent hyperopia of 3.0 to 4.0 diopters exposed by cycloplegia. The amount of correction that should be provided during surgery is controversial in such cases.

34. Treat 50–75% of the difference between the cycloplegic and manifest refraction on the top of the manifest refraction Or 100% of the hyperopia obtained by cycloplegic refraction If partial correction- pt informed about a return of hyperopia after the onset of presbyopia

35. Excimer laser profile is different for hyperopia Ablation directed toward the periphery The corneal refractive power must be increased to treat hyperopia, whereas it must be decreased to treat myopia. higher risk of developing LASIK-induced neurotrophic epitheliopathy (LINE) The higher risk d/t larger flap in hyperopia.

36. Indications for LASIK for Hyperopia 1-4 D of spherical equivalent hyperopia with or without astigmatism. Attempted correction for consecutive hyperopia after LASIK for myopia should be decreased by 0.5 diopter, there is a high risk of overcorrecting the eye back to low myopia. LASIK can also be used effectively to correct consecutive hyperopia after radial keratotomy (RK).

37. Technique and Instrumentation for LASIK for Hyperopia requires a large flap diameter, typically larger than 9.0 mm. For both primary and consecutive hyperopia, the VISX S2™ or VISX S3™ excimer laser is used with a 9-mm ablation zone

38. LASIK in Complex Cases LASIK after radial keratotomy - LASIK to be safe and effective in treating residual myopia and RK- induced hyperopia. - However preference is to utilize PRK with MMC as the primary procedure when dealing with patients after RK LASIK after photorefractive keratectomy - treating eyes with no or low haze after PRK - typically utilize PRK for the enhancement procedure also

39. LASIK after penetrating keratoplasty primary goal - allow spectacle correction. risk of corneal dehiscence during the creation of the flap as early as 8 months after PKP while others advise a minimal period of 2 to 3 y careful prep attention to the graft as well as the GHI All sutures should be removed prior

40. LASIK enhancements Performing Re LASIK Undercorrection is the m/c problem following LASIK Before enhancement, refractive stability should be present use the preoperative refraction in diopters to indicate the number of months to wait after the initial LASIK example- wait for at least 6 months in a patient with a preoperative refraction of 6 D

41. LASIK after Intraocular Lenses The surgeries can be staged-with the lens surgery performed first, followed later by PRK or LASIK Alternatively, the LASIK flap can be made at the time of the lens surgery and lifted several weeks later for the laser ablation

42. Intraocular Lens Calculations after LASIK use of postoperative average standard k readings in std IOL power formulas - substantial refractive errors hyperopia being the unexpected surprise in patients who undergo myopic refractive procedures and vice versa The keratometer is inaccurate - because it measures only the paracentral region, ignoring flatter (after myopic refractive surgery - or steeper (after hyperopic refractive surgery )

43. Methods of calculating corneal refractive power in patients who have had corneal refractive surgery include the clinical history method contact lens over-refraction videokeratography corneal tomography/Pentacam the double-K method Gaussian optics formula. Pentacam software can accurately calculate the front and back surface powers of the cornea and adjust for any power overestimate and report a term called equivalent keratometric reading (EKR) , which can then be used in IOL calculations

44. Clinical history method* Gold std algebraically add the surgically induced refractive change to the preoperative K-readings K = Kpre + Rpre – Rpo Kpre = preoperative corneal power, Rpre = preoperative refraction, and Rpo = postoperative refraction This method cannot be used if presurgical K-readings and refractive correction unknown postoperative refraction affected nuclear sclerosis-induced or axial length progression myopia *IOL Power Calculations After LASIK and PRK Giacomo Savini, MD; Kenneth J. Hoffer, MD, FACS; and Maurizio Zanini, MD https://crstodayeurope.com/articles/2007-apr/0407_09-php/

45. https://iolcalc.ascrs.org/wbfrmCalculator.aspx Online software

46. COMPLICATIONS OF LASIK satisfaction rate of 95.4%, with the most common reasons for dissatisfaction being residual refractive error, dry eyes, older age, and night vision symptoms. divided into intraoperative, early postoperative, and late postoperative complications

47. Intraoperative LASIK Complications Femtosecond laser flap complications Cavitation air bubbles Rx- gentle massage of corneal stroma Epithelial breakthrough Suction loss during flap creation - stops the laser creation of the lamellar interface causing an incomplete flap

48. Microkeratome complications Buttonhole flaps when the keratectomy perormed without adequate suction evident immediately irregular circle in the center representing the buttonhole Management flap should not be lifted Gentle interface irrigation eye is allowed to heal for at least 3 months

49. Thin flaps tend to roll along the distal cut edge Management - If smooth- LASIK can be performed If not smooth or perforations or buttonholes in the flap- flap should then be replaced and the cornea allowed to heal for 3 months.

50. Free flap when the microkeratome does not stop to create a hinge but continues across the cornea, severing the flap from the bed Management- If suctionis low and the stromal bed is irregular- flap replaced and allowed to heal without performing the excimer laser ablation If stromal bed smooth and free cap of normal thickness- ablation can be continued

51. C. Corneal perforation most feared and rare complication Without the depth plate , blade would cut straight into the cornea, causing penetration into the AC With extrusion of the intraocular contents due to IOP obvious during the advancement of the microkeratome sudden release of a jet of fluid as the cornea is penetrated followed by a loss of suction with beeping from the suction pump could be a/c extruded iris and/or lens material Management - -preserve as much intraocular tissue as possible, -suturing the corneal incision to restore the AC

52. 3. Laser-related complications Incorrect laser programming obvious postoperatively - patient does not achieve a good UCVA double check programming prior to performing LASIK. Ablation complications Irregular astigmatism Beam profile abnormalities irregular hydration particulate material falling onto the cornea may block subsequent laser pulses Decentration

53. 4.Epithelial defects l/t prolonged visual recovery postoperative pain diffuse lamellar keratitis (DLK) epithelial ingrowth Management- -continue with the laser treatment, replace the LASIK flap place a BCL if greater than 3 mm If extremely large, dont proceed with the treatment of the second eye

54. 4. Neovascular bleeding during LASIK occurs immediately after keratectomy along the superior flap edge. Management downward pressure from the suction ring - tamponade be dried with a dry Murocel spear. Continuous bleeding that could extend into the ablation area, dry rectangles of instrument wipe Iopidine is used as it is an alpha-2 agonist with a vasoconstrictive effect without the pupillary dilatio.

55. Prevention- ring can be switched to the 8.5-mm ring so that the neovascular bleeding can be minimized

56. Early Postoperative Complications Flap striae - occur when it is folded onto itself. Normally-oriented horizontally . Displaced flaps-oblique striae. Retroillumination -accurate localization of striae Fluorescein staining of the cornea - identifies subtle striae.

57. Indications for M/nt- striae that extend through the visual axis M/nt- stretch and smooth technique flap hydration with hypotonic saline epithelial debridement flap applanation phototherapeutic keratectomy flap suturing

58. 2. Dislodged flap extremely blurred vision Painful eye Patients with a dislodged flap should be treated as urgently as possible

59. 3. Infectious keratitis - infiltrates be cultured prior to starting therapy - flap lifted- infiltrate removed - interface irrigated with antibiotic and flap replacement. - m/c organism- MRSA Symptoms - pain, photophobia, watering, or decreased visual acuity. Slit lamp examination - ciliary injection, epithelial defect, AC reaction, or hypopyon M ycobacteria and fungi- seen in the interface, with a feathery or indistinct margin

60. 4. Diffuse lamellar keratitis aka Sands of Sahara Sands nonspecific diffuse interface keratitis LASIK interface keratitis (LIK) interface inflammation that occurs in the 24–72-hour postoperative period RISK FACTORS - bacterial endotoxins Epithelial defects ocular inflammation ocular trauma Other causes - cleaning solutions, talc from gloves, meibomian gland secretions, microkeratome oil, rust on instruments, blade debris, iodine skin cleaners, and CMC drops.

61. confined to the flap interface subtle DLK difficult to differentiate postoperative SPK or mild interface debris. SPK is always on the corneal surface and will stain with fluorescein. DLK is at the level of the interface and does not stain with fluorescein. There is no AC reaction DLK except in the most advanced cases.

62. Grade 1 DLK Focal granular material in the LASIK flap interface Rx- Intensive topical steroids Grade 2 DLK Diffuse granular material Rx- Interface irrigation, Intensive topical steroids Grade 3 DLK Diffuse, confluent granular material Rx - Grade 2 Plus Topical steroids and antibiotics can been placed on the stromal bed Grade 4 DLK Grade 3 plus Inflammation localized Rx- as Grade 3

63. 5. Transient light sensitivity syndrome unusual photosensitivity 2- 6 wks after LASIK performed with FSL D/t pulse energy used during flap creation Visual acuity is unaffected, slit lamp findings are minimal steroid therapy

64. Late Postoperative LASIK Complications 1. Epithelial ingrowth d/t Epithelial cells trapped under flap Risk factors - anterior BM dystrophy h/o recurrent erosions Peripheral epithelial defects Poor flap adhesion Buttonholed flaps Repeat LASIK

65. 2. Postoperative keratectasia following LASIK - after 1 to 12 months - corrections of over 8 D. - final corneal thickness of less than 400 µm - with less than 250 µm of presumed posterior corneal stroma Rx- - hard contact lenses - PKP Prevention - Patients with keratoconus or other corneal thinning disorders identified on topography should not have LASIK

66. 3. Central islands area of higher refractive power of more than 1.5 D and 2.5 mm Rx- Customized wavefront laser correction 4. Night vision disturbances: halos and glare 5. Irregular astigmatism 6. Post-LASIK dry eyes- -creation of a temporary neurotrophic cornea by severing the corneal nerves - The cause of the dry eye is decreased corneal sensation withdecreased feedback to the lacrimal gland with reduced tear production Rx- frequent lubrication, Punctal plugs in upper punctum , silicone plugs in the upper punctum, bedroom humidifier and protective sunglasses

67. 7.Vitreoretinal Complications after LASIK - theoretical risk of increased occurrence of RD after LASIK due to the alteration of anterior retina by the suction ring - lattice degeneration (0.3%), posterior vitreous detachment (0.1%), macular hemorrhage (0.1%), retinal tear without retinal detachment (0.1%),and choroidal neovascularization (0.1%).

68. EPILASIK / LASEK Anterior stroma of cornea (ant. 1/3 rd) has stronger interlamellar connections than post. 2/3 rd . So surface ablation preserves the structural integrity better than LASIK especially in the correction of moderate to high myopia.

69. LASEK-Camellins Technique - 20% absolute alcohol used for 20-35s T o raise epithelial flap. Flap reposited after ablation

70. EPILASIK Epithelial keratome used to lift epithelial flap of about 60-80µ thick.

71. Thin-flap LASIK also referred to as sub Bowmans keratomileusis allow LASIK to be done more safely with regard to ectasia and corneal hypoesthesia pendular mechanical microkeratomes Femtosecond lasers

72. THANKYOU