Refractive surgery part 2 myopia

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Refractive surgery part 2 myopia

  1. 1. REFRACTIVE SURGERY PART 2 VIJAY JOSHI
  2. 2. LASER SUBEPITHELIAL KERATOMILEUSIS (LASEK)  Introduced by Massimo Camellin in 1999.  LASEK combines advantages and features of both PRK and LASIK.  It involves removal of an epithelial flap ( chemically loosened with alcohol) before ablating the corneal stroma with Excimer laser.
  3. 3. SURGICAL PARAMETERS AND TECHNIQUE  LASEK resembles PRK more than does LASIK, so surgical considerations are similar, except following features:  Epithelium removal in LASEK is in form of hinged flap.  Steps are:  Trephining: an epithelial trephine (8.5-10.5mm in size) is placed on the center of anaesthetized cornea.  By gentle pressure on the cornea the trephine cuts the epithelium, sparing the underlying stroma and 4mm epithelial hinge.
  4. 4. SURGICAL PARAMETERS AND TECHNIQUE  Alcohol treatment: After epithelial trephining, a similar sized alcohol well is centered on the cornea.  The well is filled with 20% ethyl alcohol and kept in position for 60 secs.  The alcohol is then removed with a cellulose sponge and the well is taken off the cornea, and epithelium is washed with BSS.  Separation of epithelial flap: after waiting for a minute (during which the alcohol treated epithelium is loosened from the underlying bowman’s membrane), a microhole is used to pick up the epithelium rom the edges of trephine marks
  5. 5. SURGICAL PARAMETERS AND TECHNIQUE  Corneal stromal ablation: is then carried out to correct refractive error( as described in PRK)  Reposition of epithelial flap: after ablation the corneal surface is washed thoroughly and scrapped to rid of the debris and condensed plume.  Then the epithelial flap is carefully rolled back with the help of an irrigating cannula.  Bandage contact lens: is then applied over the cornea for 5-7 days
  6. 6. LASEK
  7. 7. LASEK WITH MITOMYCIN -C  Some surgeons use 0.02% Mitomycin C for 30 secs after corneal ablation and through wash with BSS before reposting the epithelial flap.  Mitomycin C is useful in curtailing the fibroblastic activity and thereby reducing and delaying the chances of corneal haze-more so when treating high myopia.  Post Operative Mx is similar to that in PRK and LASIK.
  8. 8.  Advantages of LASEK over PRK:  Less postoperative pain.  Early recovery and less postoperative haze due to improved epithelial healing.  ADVANTAGES OVER LASIK:  Corneal Ectasia is less likely as residual corneal bed thickness is more.  Flap related complications like button hole, partial flap, free caps, lost flap, flap wrinkling and epithelial down growth are less known.  Additional correction of myopia upto 5 D more than LASIK is possible, as another 90u of corneal stroma is available for ablation.  In thin cornea, LASEK is better option than LASIK  Increase in high order aberrations, noted with LASIK is excluded with LASEK.  Postoperative dry eye chances are less as the corneal nerves are not severed as with LASIK.  Large zone treatment is possible with LASEK. In LASIK the flap size is a restricting factor to the size of the treatment zone.
  9. 9. LASEK VS LASIK : PRESENT STATUS  Presently LASEK is a good alternative to LASIK where the latter is a handicap E.g in patients with myopia >8D and in those with thin cornea.  However, LASEK is not preferred over LASIK because of following disadvantages:  Postoperative pain is more  Delayed recovery, i.e vision remains blurred for 7-10 days  Corneal haze similar to PRK is definitely encountered on long term follow up.
  10. 10. EPIPOLIS LASER IN SITU KERATOMILEUSIS ( EPI-LASIK)  Epi- Lasik is just like LASEK except that in it the epithelial flap is created with the help of an ‘Epikeratome’ and thus the epithelial cells are not damaged by chemical toxicity of alcohol.
  11. 11. SURGICAL TECHNIQUES AND POSTOPERATIVE MANAGEMENT  Surgical technique and postoperative management of a case of epi- LASIK is same as that of LASEK except the technique of creation of epithelial flap which is described below:  Creation of epithelial flap: made with help of epikeratome.  Epikeratome travels across the eye more slowly than the microkeratome.  This gives better control over the separation.  Epikeratome: has a blunt blade or separator made of either plastic or stainless steel which cleaves or pushes away a much more smoother epithelial flap.
  12. 12. EPI LASIK
  13. 13. EPI-LASIK
  14. 14.  Advantages of epi-LASIK:  Advantages of epi- LASIK over PRK and LASIK : are same as that of LASEK.  Advantages of epi-LASIK over LASEK:  The use of epikeratome eliminates the need for the alcohol used in LASEK.  Since the alcohol is toxic to epithelial cells, avoiding alcohol application in epi-LASIK results in:  Less pain  Faster healing  Less corneal haze
  15. 15. REFRACTIVE SURGERY CHARACTERISTICS
  16. 16. C LASIK DEFINITION  Custom ablation is an ablation pattern that attempts to optimize eye’s optical system using a variety of spherical, cylindrical, aspherical & asymmetrical Rx based on individual eye’s optic & anatomy as well as the pt needs.  The exact assessment of individual eye’s optic is made by Corneal Topography & Aberrometry.  The customized ablation highlights that it selectively corrects the inherent aberrations of each individual eye.
  17. 17. TYPES OF CUSTOMIZED ABLATION  2 forms:  Corneal topography guided ablation: takes care of ocular aberration detected by corneal topography & treats the irregularities as an integrated part of laser Rx plan.  Wavefront guided ablation: treats the aberrations of the entire human optical system that are measured by a variety of wavefront measurement devices
  18. 18. ABERRATIONS  Although the human eye is an optical marvel, yet it suffers many deviations from being an ideal optical system.  All forms of deviations (refractive errors) are basically aberrations.  Aberrations can be grouped as:  1. LOWER ORDER ABERRATIONS: include myopia, hypermetropia and regular astigmatism.  2. HIGHER ORDER ABERRATIONS: are subtle deviations from ideal optical system.  These include spherical aberrations, chromatic aberrations, coma, decentering, oblique aberration and centering.  The higher order aberrations do not lend themselves to easy solutions.  Thus, the higher order aberrations limit the potential visual acquity of the eye.
  19. 19. CUSTOM LASER IN SITU KERATOMILEUSIS  LASIK corrects only low order aberrations such as spherical and cylindrical refractive errors.  The high order aberrations which effect the quality of vision but not significantly the Snellen visual acuity are not corrected by standard LASIK procedure.  Rather, the conventional laser Rx on the cornea increases high order aberrations, especially at night when the pupil dilates.  The aberrations are increased because the normal cornea is prolate in shape( steeper in the centre), but it becomes oblate ( steeper in the periphery) after conventional ablation profile.
  20. 20. CUSTOM LASER IN SITU KERATOMILEUSIS  These aberrations are probably the reason for deterioration of visual performance in some eyes after conventional photorefractive procedures.  Besides this, there are cases with irregular astigmatism following eg. Penetrating corneal grafts, penetrating injuries or peripheral corneal scar, which are not amenable to conventional ablation procedures.  Custom LASIK tackle the above listed problems.
  21. 21. C LASIK PROCEDURE 1. MEASUREENT OF THE OPTICAL ABERRATION OF THE EYE:  Corneal topography and wavefront aberrometry: systems have been developed to measure all the optical aberrations of the eye.  These measuring devices have the ability to measure refraction to submicron level of about 0.01 D.  A wave print of the eye is created.  This information is used to prepare a customized laser ablation pattern.
  22. 22. C LASIK PROCEDURE CONTD..  2. LINKING THE MEASURED OPTICAL ABERRATION TO THE LASER MACHINE:  The software is available that combines all the measured data which is then downloaded into a floppy disk and inserted into the laser machine computer.  3. LASER ABLATION:  Customized ablation requires a flexible laser system that can deliver a small spot( less than 1.0-2.0mm) or use an erodible mask customized to a very subtle level, and an excellent eye tracking system or an eye immobilizing system.
  23. 23. C- LASIK
  24. 24. C LASIK
  25. 25. ADVANTAGES  1. High quality vision: C- LASIK provides a high quality vision which is comparatively free from night glares, halos and has improved contrast sensitivity.  2. Supervision: human eye has much better potential visual acuity of about 6/2 to 6/1.5  This is greatly reduced by diffraction of light and the high order aberration of the eye.  There fore, by customized ablation, which takes care of the aberrations of the eye, it is possible to achieve supervision to the tune of 6/4 or 6/3.
  26. 26. ADVANTAGES CONTD..  3. Less invasive technique:  Lesser amount of tissue ablation is require to achieve the given effects.  4. Can correct irregular astigmatism
  27. 27.  Commercially available systems for customized ablation are:  Zyoptix  ORK corwave  Nidek NAVEX LASIK system with optical path difference.
  28. 28. INTRALASE LASER  The IntraLase ultrafast femtosecond laser is the first bladeless laser technology for performing LASIK.  Step One: Corneal flap creation by means of femtosecond laser.  The laser uses an infrared beam of light to precisely separate tissue through a process called Photodisruption.  In this process, the focused laser pulses divide material at the molecular level without the transfer of heat or impact to the surrounding tissue.  IntraLase creates the flap from below the surface of the cornea, using an "inside-out" process.
  29. 29. INTRALASE LASER  The silent beam of laser light is focused to a precise point within the stroma (central layer of the cornea) where each pulse of the laser creates a tiny 2- to 3-micron bubble of carbon dioxide and water vapor.  Thousands of these microscopic bubbles are precisely positioned to define the flap's dimensions, as well as the location of the hinge.  Bubbles are then stacked along the edge of the flap up to the corneal surface to complete the flap.  The process from start to finish takes approximately 22 seconds
  30. 30. INTRALASE LASER  In Step Two:  Flap is opened, so that an excimer laser can be used  Flap is then returned to its original position where it seals without stitches.  IntraLase spares more of the sensory nerves in the cornea responsible for reflex tearing than the manual keratome, beneficial in dry eye pt as compared to LASIK.  IntraLase also places less pressure on your eye than the microkeratome.  Aside from comfort considerations, this creates greater safety for patients who are glaucoma suspects.  IntraLase can also allow some of those who were not previously considered candidates due to thinner corneas, the ability to have the procedure.
  31. 31. SURGICAL STEPS
  32. 32. INTRALASE LASIK
  33. 33. ADVANTAGES  iLASIK is:  100% blade-free – combines all the latest all-laser technology.  100% customised – tailored to the unique characteristics of your eyes.  Incredibly safe – one of the safest medical procedures in the world.  Highly effective – the majority of patients experience 20/20 vision or better.  Fast & virtually painless – it only takes a few seconds to correct each eye.  Suitable for almost everyone – more people treated than ever before
  34. 34. RELEX AND SMILE  Traditional laser surgery involves cutting a flap off the front of the cornea or pushing the outer cells of the eye to one side and using a laser to change the shape of the cornea.  With ReLEx there is no flap cut.  Possible only with the VisuMax Laser from Carl Zeiss  Two Procedures  FLEx -Femtosecond Lenticule Extraction  SMILE -Small Incision Lenticule Extraction
  35. 35. THE RELEX PROCEDURE: HOW IT WORKS  ReLEx mainly consists in the creating micropulses beneath the surface of the cornea, or lamella, a disc- shaped piece of corneal tissue.  This represents a considerable difference between ReLEx and LASIK.  In fact, the lenticule incision, performed with the femtosecond laser, is conducted at the same time of the creation of a corneal flap from which the surgeon is able to take the lenticule.  Finally, after the lenticule is removed from the surface of the cornea, the flap is repositioned
  36. 36. THE RELEX PROCEDURE: HOW IT WORKS
  37. 37. RELEX AND SMILE  “Several great advances come from not having to create a flap or disturb the front of the cornea; the level of correction can be much higher without weakening the cornea.  People who are contact lens intolerant can now be candidates as there is little or no dry eye after ReLEx.
  38. 38. CORNEAL RESHAPING WITHOUT ABLATION  Excimer laser performs photoablation.  The photo ablation rate increases linearly with fluence [flux] (defined as the total number of particles that intersect a unit area in a specific time interval of interest, and has units of m–2 ), beyond a certain threshold.  Excimer Laser fluence and photoablation rate gets influenced by various factors:  corneal hydration levels, humidity levels, the presence of organic vapour's, the depth of ablation  This results in a scatter, especially for the treatment of high myopia
  39. 39. REFLEX AND SMILE  A refractive lenticule is created in the intact cornea and removed through a small incision. No need for point-by- point ablation as with an excimer laser. No flap.  Reflex uses cutting instead of ablation  A binary process instead of linear.  Much less influence of any external factors reflected in the tremendous accuracy achieved.  Results are especially interesting for high myopia, a group in which excimer lasers don’t fare as well
  40. 40. INDUCTION OF ABERRATIONS  Excimer lasers suffer from peripheral fluence loss  Fresnel reflection losses at a high angle of incidence  Increase in spot size in the periphery  Leads to an increase in spherical aberrations  Minimized by newer ablation profiles  However, with ReLEx, this problem is essentially not there.  Should lead to less induction of spherical aberration
  41. 41. SO WHEN IS AN EXCIMER NEEDED  Wavefront Guided Procedures (< 5% of a normal refractive practice)  Retreatments (< 1% in ReLEx procedures)  Hyperopia (Latest results of ReLEx for Hyperopiaare quite encouraging)
  42. 42. BENEFITS OF REFLEX OVER OTHER REF SX  No risk of flap displacements (There is a cap. There is no flap!!!)  With no flap displacement even after trauma, this is a better option for those involved in close- contact sports or jobs with chances of injuries.  Small Incision results in minimal cutting of corneal nerves.  Less dry eyes, smaller reduction in corneal sensitivity.  Less discomfort for the patient for a smaller period  Possible better biomechanical stability relative to Femto- LASIK.  ReLEx is faster to perform than LASIK as only one laser is used.  ReLEx may be potentially reversible, while LASIK is irreversible.  An 80% lesser cut means that the chances of complications like infections, ingrowth of the epithelium, etc. are drastically reduced.
  43. 43. BENEFITS OF REFLEX OVER OTHER REF SX…  Suction applied during surgery is restricted to the cornea. This ensures that side effects seen commonly with other techniques like sub-conjunctival hemorrhage (bleeding under the conjunctiva) is significantly lesser.  The FBS experienced by patients at the time of corneal healing after the operation is reduced to 2-3 hours as compared to 4-5 hours in LASIK and 2-3 days in PRK.  It does not produce the smell of burnt tissue as seen with an excimer laser and there is no blackout of vision during the procedure as there is no occlusion of the central artery.
  44. 44. D. MISCELLANEOUS CORNEAL REFRACTIVE PROCEDURES FOR MYOPIA  Miscellaneous corneal refractive procedures  Orthokeratology  Intacorneal contact lenses  Intrastromal corneal ring segments (INTACS)  Gel injectable adjustable keratoplasty
  45. 45. ORTHOKERATOLOGY  Is an non surgical reversible method of moulding the cornea with over night wear of unique rigid gas permeable contact lenses to correct myopia.
  46. 46. PROCEDURE  1. Meticulous refraction: to ascertain the exact amount of spherical and cylindrical lens to correct the myopia.  2. Corneal topography: to map the shape of anterior surface of cornea.  3. Calculations of parameter of corrective contact lenses: are then made from the observation of corneal topograph and exact amount of refractive error to be reserved.  4. Manufacturing of special contact lenses: which produce the desired effect for reshaping of the patient’s cornea is ordered.  5. Wearing schedule: after desired correction s made, the lenses may only be needed to be worn a few hours a day for about 3 days a week to keep the cornea in shape necessary to see clearly without glasses and without CL.
  47. 47. INDICATIONS  Is useful at any age with spherical prescription less than -4 D and astigmatism less than -1.5 d.  This a great alternative for:  Those who are too young to consider LASIK of any age below 18 yrs.  Refractive error has not been stabilized.  Those youngsters and teenagers who are involved in sports where wearing contact lenses or glasses might be limiting their sports activity
  48. 48. ADVANTAGES  1. Non surgical method  2. Available for most people, even younger  3. Freedom from constant corrective lens wear  4. Better vision improvement  5. Reversible method
  49. 49. DISADVANTAGES  1. Longer result time  2. Not a permanent solution  3. Higher startup cost than regular contact lenses or eye glasses.  4. Currently only for myopia
  50. 50. INTRACORNEAL RINGS  Are implanted into the peripheral cornea, producing a vaulting effect that flattens the central cornea and corrects myopia of upto 3 D  Features of Intracorneal rings include:  Made of PMMA  Outer dia 8.1mm  Inner dia 6.7 mm  Arc length 150º  Positioning hole dia 0.28mm  Rings cross section – hexagonal  Each package consists contains two rings- right and left  Thickness – available in five different thickness inserts 0.25, 0.30, 0.35,0.4 and 0.45mm
  51. 51. INDICATIONS OF INTACS  Myopia: pt with low degree myopia -1.O –3.5 D who are willing to get rid of glasses.  Other indications: keratoconus, pellucid marginal degeration, and post LASIK corneal ectasia.
  52. 52. CONTRAINDICATIONS  Collagen vascular ds  Autoimmune or immunodeficiency ds  Pregnant or nursing women  Presence of ocular conditions such as recurrent corneal erosion syndrome  Corneal dystrophy that may predispose the pt to future complications
  53. 53. SURGICAL TECHNIQUE  Topical Anaesthesia  Marking of geometric centre of cornea is done with help of 11mm zone marker.  Corneal thickness is measured at the site of the planned incision.  An incision, 1.2mm in length , is made with a sharp diamond blade at 12 o’ clock position.  Corneal tunnels(pockets) are then created at approximately 2/3rd stromal depth using pocketing hook.  Insertion of Intacs: is then done maintaing a space of 2mm between their ends at 6 o clock and space of 1.5mm btwn their ends and the edge of the incision at 12o clock position.
  54. 54.  Intracorneal ring. After a peripheral circular lamellar dissection, two polymethyl methacrylate ring segments of predetermined diameter and thickness are inserted. The midperipheral anterior lamellae are lifted focally by the ring segments, which results in a compensatory flattening of the central anterior lamellae and hence a decrease in the refractive power of the cornea.
  55. 55. SURGICAL TECHNIQUE
  56. 56.  Postoperative Rx  Antibiotic/steroid combination: QID *2-3 wks  Lubricating artificial tear: QID* 4 wks  Advantages of Intacs over LASIK include:  Maintain normal positive aspherity.  Preserve corneal stroma  Reversibility  Changeable  Rapid visual recovery  Safety and cost effective  Disadvantage of Intacs:  Non effective in myopia >4 D  Complications like under/ over correction, neovascularization, extrusion and visual side effects
  57. 57. INTRACORNEAL CONTACT LENSES  Have also been tried but never became popular
  58. 58. GEL INJECTABLE ADJUSTABLE KERATOPLASTY  Is being tried in pt with -1 to -4 D myopia.  A non-toxic semisolid gel is injected in paracentral stroma after making a tunnel as described in Intacs  Potential advantages include ease of manipulation , adjustability and reversibility
  59. 59. INTRAOCULAR REFRACTIVE SURGERIES FOR MYOPIA  A. Refractive lens exchange (extraction of clear crystalline lens)  Extraction of clear lens had been advocated for myopia -16 t0 -18D, especially in U/L cases.  Zero power IOL is better than no IOL , since it not only retards PCO but also minimizes the incidence of RD.
  60. 60.  Indications  Refractive errors with associated lens opacities , specially in presbyopic age.  High refractive error, myopia of >10 D and hyperopia of > 5 D are ideal for RLE.  Contraindications:  Retinal ds that are potentially vision imparing.  Occupational night drivers.
  61. 61. INTRAOCULAR REFRACTIVE SURGERIES FOR MYOPIA  B. Phakic refractive lenses:  IOL of appropriate power is implanted inside the eye, without touching the normal crystalline lens, thus without disturbing the accommodation.  ADVANTAGES:  Safe & predictable  Reversible  Inexpensive equipment  LASIK can be performed for residual refractive error (bioptics)
  62. 62.  Disadvantages of PRL’s :  Corneal endothelium decompensation  Chronic uveitis  Cataract formation  Retinal detachment  Endophthalmitis
  63. 63. SUMMARY  Low to moderate myopia: -1 to 10 D  LASIK/ C-LASIK: -1 TO -10D  Epi-LASIK : Thin cornea & -6 TO -10 D  INTACS: -1 TO -3 D  ORTHOKERATOLOGY: -1 TO -3 D below 18 yrs of age.  High myopia:-7 to -10 D  PRL  RLE (preferred after 40 yrs of age)

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