Keratorefractive surgeries


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  • Today the filed of refractive surgery has evolved to include many modalities for the treatment of different refractive errors.
  • Motivation: detailed information, procedure xplained to the pt anxiety levels xplained. REFRACTION: stability of the refraction last 1 year is checked, >0.5D change accounts for unpredictable long term result. PUPIL SIZE: PUPIL SIZRE BOTH IN LIGHT & DARK should be measured,pupillometer can be used to measure pupil size, pts with larger pupil should be unstd glare & haloes Corneal thickness: topography to rule out keratoconus, its C/I in LASIK due to central corneal thinning, 250mm be left beneath a lamellar keractectomy in order tp prevent ectasia
  • Hartmann: small light projected to retina and reflected back and focused by lenselet arrey this recorded by video sensor and compared with theoritical aberration free sysytem.
  • For myopia conves portion is removed and for correction of hyperopia concave portion is removed
  • Refraction 0.5 spherical chnage / 0.25 cylindrical change / < 20 degree axis change in one year
  • The well is filled with 20% ethyl alcohol solution for 30 to 50 seconds. Longer times are recommended for young men, postmenopausal women, and long-time contact lens users, because the epithelial flaps in these groups of patients are generally more difficult to lift. At the end of the allotted time, an absorbent cellulose surgical spear is used to soak up the alcohol in the well.
  • Sampling rate: Rate refers to how frequently the tracker measures the eye position.varies from 60 Hz to 400 Hz Latency: time required to determined eye’s location, in close loop system such as laser radar based system gives continuous feedback occurs leads to zero latency. Its infrared camera based tracking systems. Tracker type: two types:::: video tracking: infrared light of iris against a dark pupildeviation of the eye is read & corrected. Laser radar: space stabilised image is maintained & eye position calculated continually. OPEN SYSTEM: new image is taken n compared with old image change in location is calculated. CLOSE: cont monitoring using a radar system.
  • They do not control progression of the keratokonus, just help for the fitting of the lens
  • Its not approved method still under trial, however riboflavin increases the absorption of the radiation & penetration to the deeper tissues, its increased structural integrity shows sucess in various studies of treating and progressing KCONUS.
  • Averg corneal penetration is 480-530 mm which is 80-90% of corneal thickness, effect was found to vary directly with the pulse energy & inversely with the distance from the centre of the cornea.
  • Error of application would be less in non contact mode, refractive stability & reproducibility is greater. Ho: YAG laser & the alignment of the burns, have shown that using more than one ring produces a greater refractive change & that applying the concentric rings. STATS: various studies shown improved vision between with 0.75 to 4.75D preoperatively of spherical, up to 3DS astigmatism less then 1DC.
  • 80% depth of the cornea homogenously thermalenergy is deliveredless then 0.5D of difference in the manifest & cycloplegic refractions can be corrected. C/I: recent chnages in 1 yr, age <21 yr, dry eye, C dystrophies, glaucoma, herpes, keloid, keratoconus, DM, PREGnancy, autoimmue & vascular disorders.
  • Keratorefractive surgeries

    2. 2. APPLIED ANATOMY OF CORNEA • EPITEHLIUM: composed of non keratinized startified squamous epithelium of 4 to 6 layers thickness. BM (lamina densa & lamina lucida), wing cells and flattened top cells having microvilli. • BOWMAN’S LAYER: condensed superficial layer of the stroma, consists of randomly dispersed collagen fibrils. • STROMA: 500m thick consists of collagen producing fibroblasts keratocytes , matrix & collagen lamellae.
    3. 3. APPLIED ANATOMY OF CORNEA • DESCEMETS MEMBRANE: strong well defined sheet in between stroma & endothelium. • ENDOTHELIUM: plays an major role in active transport & maintenance of normal stroma.
    4. 4. HISTORY • In 1978 bore,myers & cowden were first in USA to perform radial keratotomy & report there results. • Lamellar surgery were evolving simultaneously, Jose Barraquer was the first to correct refractive error through lamellar surgery.
    6. 6. INDICATIONSINDICATIONS • MYOPIA : Photorefractive karatoplasty. LASEK. LASIK. HYPERMETROPIA : PRK/ LASEK 2-3D LASIK upto 4D Conductive keratoplasty Laser thermal keratoplasty
    7. 7. INDICATIONSINDICATIONS • ASTIGMATISM : Limbal relaxation/ arcuate PRK/LASEK upto 3D LASIK upto 5D Conductive keratoplasty • PRESBYOPIA : Conductive keratoplasty
    9. 9. Clinical significance of cornealClinical significance of corneal topographytopography • Indispensable tool for refractive surgeons – Preoperative screening – Surgical planning – Assessment of surgical outcomes – Detection and management of complications – Refinement and development of surgical techniques
    10. 10. Principles of Corneal TopographyPrinciples of Corneal Topography • Placido disc system • Non-Placido disc system –Scanning slit –Rasterstereography –Laser Holographic interferometry
    11. 11. FIGURE 2-17 BASIC CHARACTERISTICS OF AN AXIAL MAP Simulated keratometer and astigma- tism indicator Statistical index indicators Pupil size indicator Dioptric power and radius indicators Vertex and pupil distance and location indicators 1mm x 1mm grid indicators Center of map (vertex) and center of pupil markers Pupil marker
    12. 12. KeratometryKeratometry • Advantages • Accessibility • Ease of use • Precision is good • Low cost • Adequate for most contact lens fitting • Limitations • Small area measured: periphery and apex not measured. • Assumes that the cornea is a spherical surface: accuracy is questionable • Irregular topography not described specifically and sometimes undetected
    13. 13. WAVEFRONT • Discovered nearly 400 years ago by christopher scheiner. • He demonstrated a technique to measure the refractive error of the eye using a device known as Scheiner disc. • Visual acuity measuring device takes into consideration tear film, anterior corneal surface, corneal stroma, posterior corneal surface, anterior crystalline lens
    14. 14. • posterior crystalline lens surface, vitreous and retina. • Prior to the advent of wavefront-sensing devices, clinical refraction consisted of three data points for each eye: defocus (spherical error, myopia, or hyperopia), astigmatism, and axis.
    15. 15. Wavefront Technology Diagnostic devices : 1. higher-order aberrations : field curvature, distortion, diffraction, spherical aberration, chromatic aberration, coma 2.refraction vs. wavefront refraction (refractive map) cf. keratometry vs. topographic map Wavefront-guided refractive surgery
    16. 16. Types of aberrometer • Hartmann shack system outgoing reflection aberrometry) • Tscherring system • Ray tracing system. • Ingoing adjustable refractometry. • Double pass aberrometry.
    17. 17. Note the loss of dots centrally in a “moth-eaten” appearance and the overall irregularity of horizontal and vertical alignment of the spots of this eye with significant aberration.
    18. 18. EPIKERATOPHAKIA • Is an form of refractive surgery on the cornea for the correction of keratoconus, aphakia & high myopes. • Gasset and kauffman in 1968 tried with plastic lens, glued over the cornea. Unfortunately glue made the corneaq opaque. • Werblin and kauffman later devised using lathe cut donor corneal lenticule mainly in peadiatric aphakic patients. • With planopower lenticule was developed to treat keratoconus like onlay lammellar keratoplasty.
    19. 19. EPIKERATOPHAKIA • Corenal epithelium is thoroughly denuded by rubbing with cellulose sponge. • 7mm to 7.5mm trephine is used to incise the patient’s cornea partially to the depth of 0.2 to 0.3mm. • Rehydrated epikeartophakia lenticule is sutured into the host cornea. *
    20. 20. ALLOPLASTIC REFRACTIVE KERATOPLASTY • This technique involves intrastromal implantation of hydrogel materials with specific curvature. • Alloplastic material like polysulphone is placed between epikeratophakia graft & BM alters the refractive power by changing the refractive index of stroma. • Shape of lenticule is concave or convex depends on refractive status of eye ie: myope/ hypermetrope
    21. 21. KERATOPHAKIA Lenticule with predetermined power is made from the donor cornea. This lenticule is placed over the host prepared stroma with convex surface anteriorly. The previously removed stromal disk is sutured over the lenticule. Corneal decompensation may lead to postop opacification, perforation & flattening of Ac may occur. PK may require for the complication.
    22. 22. EXCIMER • Trokel, srinivasan & barren first suggested the use of excimer for corneal surgery. • Excimer derived from term excited dimer of inert gases. Leads to emission of high energy photon of UV light having 6.4eV. various excimer lasers are: argon fluoride 193nm,kypt cl 222nm, kypt fl 249, xenon cl 308, xenon fl 351.
    23. 23. Corneal tissue interaction • Carbon- nitrogen bonds which forms the peptide in proteins is broken by the highly excited state of an inertgases. • The photon induced molecular decomposition results in abalative photo decomposition. • The above mentioned process if precisely controlled, restricted, gives optically smooth, with minimal scarring with appro depth abalation.
    24. 24. Photo refractive keratoplasty • Patients selections; motivation age >18years refraction stability Ocular pathology systemic condition ocular Keratoconus Advanced keratitis sicca Lagophthalmos Corneal vascularisation Pathological changes in retina & lens Herpes depressed Corneal scar Progressive myopia. Systemic Collagen vascular disease Immunodeficiency Keloid formation Dm Pregnancy & lactation
    25. 25. PREOPERATIVE EVALUATION • Visual acuity with cycloplegic refraction • Complete ophthalmic & medical history. • Keratometry / topography / pachymetry • Pupil size and diameter in dim light. • Applation tonometry • Test for dry eye & lacrimal examination
    26. 26. PRK • Laser caliberation & prechecks • Ppd & topical anesthesia • Determination of optical centre. • Removal of epithelium • Stromal ablation • Postop medication • Placement of soft contact lens • ***
    27. 27. COMPLICATIONS • Intra OP: Error in laser programming. Incompelete epithelial removal Decentered ablation. Post OP : Early Delayed wound healing Infection NSAIDS infiltrates AB precipitates CORNEAL melts INTERMED 2wk-6 mnth Over/under corr Regression Streep corneal islands Scars Steriod induced complicationss LATE >6 months Steriods induced Scars Halos/ glares Visual fluctuations Corneal haze
    28. 28. LASEK • Laser subepithelial keratomileusis (LASEK) is a relatively new refractive surgical technique that purportedly combines the advantages of laser in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). • In 1996, Azar [8•] performed the first LASEK procedure, which he called “alcohol-assisted flap PRK.” Later it was renamed LASEK by Camellin, who popularized his own version
    29. 29. LASEK • LASEK is in essence a hybrid of PRK and LASIK that may provide relatively quick visual recovery, while eliminating virtually all flap-related complications. • The LASEK procedure is based on chemically reducing the corneal epithelial adhesion to the underlying Bowman’s layer by the application of dilute ethanol. • 8.0-mm diameter circular marker with an 80μm deep cutting edge, designed to create a 270° superficial punch cut in the epithelium.
    30. 30. LASEK • The denuded corneal surface is then ablated with the excimer laser as in standard PRK. • flap is gently repositioned over the central cornea with a blunt instrument, such as a Barraquer iris sweep. • A therapeutic soft contact lens is placed onto the cornea.
    31. 31. LASIK • Initially described by Pallikaris in1990. • Preoperative consideration; Patient selection. Stability of refraction. Fundus Corneal thickness/ conus Patients anxiety/ sedation.
    32. 32. LASIK procedure • Anesthesia : topical with 1% proparacaine or 4% xylocaine. • Corneal marking: ensure proper realignment. • Suction ring: placed on the eye & centerd over the limbus. IOP rises over 60mm hg. • Microkeratome: when adequate pressure is obtained surface is lubricated with anesthesia not saline.
    33. 33. Microkeratome is slide over surface to raise the epithelial flap. • Excimer laser reshapes the cornea by removing a pre-determined precise amount of tissue. • The corneal flap is repositioned iris sweep – no stitch required. • Fluence test. • ***
    34. 34. CORNEAL BIOMECHANICS • Layered corneal is permanently severed following surgery. • This reduces the tension in the remaining peripheral segments allowing expansion of peripheral layers. • Peripheral expansion results in higher order aberrations. • Topography allows to visualise actual change in shape that occured following the ablation. • Wavefront helps in to fully characterised shape changes & resultant functional response.
    35. 35. Customized Refractive Surgery Functional customization based on patient’s need Anatomical customization Optical customization
    36. 36. Customized Refractive Surgery Functional customization based on pt’s need 1. age 2. presbyopia 3. occupational and recreational needs 4. refraction 5. psychological tolerance
    37. 37. Customized Refractive Surgery Anatomical customization 1. corneal diameter and thickness 2. pupil size 3. anterior chamber depth 4. anterior and posterior lens shape 5. axial length
    38. 38. Customized Refractive Surgery Optical customization 1. customization based on corneal topography 2. customization based on wavefront measurement
    39. 39. Customized refractive surgery 1}SCANNING SPOT: spot size of 1mm or lesser to treat 4th order aberrations with optical zone diameter of 6mm. 2}SCANNING SPOT SHAPE: (a) Gaussian beam shape: it allows very smooth overlape creation of ablation zone. (b)Top HAT: gives rise to spikes & valleys in the ablation profile. 3}SCANNING SPOT RATE: small spots utilise 200Hz energy.
    40. 40. 4} SPOT PLACEMENT: spot is best when it is non- sequential such that one spot is not placed next to the precedding spot. EYE TRACKING: 1) SAMPLING RATE. 2)LATENCY. 3) TRACKER TYPE. 4) CLOSE-LOOP VERSUS OPEN LOOP TRACKING.
    41. 41. Wavefront-Guided Refractive Surgery “ Super Vision ” ( 20 / 10 ) Eliminating surgically induced aberrations is the first step to super vision. Seiler T : increase in higher-order aberrations after standard LASIK : 144 % after wavefront-guided LASIK : 40 % Adding wavefront informations is helpful in cases within 0.25 D of the intended correction.
    42. 42. FEMTOSECOND LASER • The femtosecond laser is a mode-locked, diode pump,neodynium-glass laser. It operates in the infrared wavelength range, at 1053 nm. It uses a spot size of less than 3 μm and produces tissue disruption (Photodisruption) at a specified and precise level within the corneal stroma. The laser produces cavitation bubbles consisting of water and carbon dioxide which are ultimately absorbed through the corneal endothelium.
    43. 43. FEMTOSECOND LASER • A unique feature of the femtosecond laser is its ability to produce tissue disruption at very low energy settings. This is due to the very short pulse width, or pulse duration, associated with the laser (600 to 800 fs), and to the very rapid pulse repetition, or speed, of the laser (15,000 to 60,000 pulses per second).
    44. 44. FEMTOSECOND LASIK • Femto laser has been devised to raise LASIK flaps MECHANICAL FEMTOLASER Mechanism Cut from side to side with globe pressure Creates an interface cut at predetermined depth Flap Meniscus flap Planar flaps Flap thickness Depends on suction ring thickness,corneal diameter & curvature Independent of any such parameters Size & shape Makes an D shape flap Well centered flap is created Complications Free flap, button hole are common Light sensitivity, photophobia common but self limiting
    45. 45. FEMTOSECOND DISADVANTAGES • Longer suction time • More flap manipulation • Opaque bubble layer may interfere with excimer ablation • Bubbles in the anterior chamber may interfere with tracking and registration • Increased overall treatment time
    46. 46. FEMTOSECOND DISADVANTAGES • Difficulty lifting flap >6 months • Increased risk of diffuse lamellar keratitis • Increased cost • Need to acquire new skills • Delayed photosensitivity or good acuity plus • photosensitivity (GAPP), which may require • prolonged topical corticosteroid therapy
    47. 47. Contraindications of LASIK • Pre existent anamolies- keratoconus. • Inappropriate parameters; power/ pachymetry/ pupil size. • Degenrative eye conditions: lupus/glaucoma/DR/ RA. • Infections. • Severe dry eye. • RD • Pregnancy/ lactating. • AGE and change in refraction.
    48. 48. COMPLICATIONS OF LASIK • Overcorrection: Myopic or hyperopic surface ablation typically undergoes some degree of regression for at least 3- 6 months. • Undercorrection: Undercorrection occurs much more commonly at higher degrees of ametropia because ofdecreased predictability due to the greater frequency and severity of regression. • Central Islands: A central island appears on computerized corneal topography as an area of central corneal steepening
    49. 49. • Optical Aberrations :Some patients report optical aberrations after surface ablat ion and LASIK, including glare, ghost images, and halos • Decentered Ablation • Corticosteroid-Induced Complications • Dry Eye and Corneal Sensation • Infectious Keratitis • Persistent Epithelial Defects • Sterile Infiltrates
    50. 50. • Corneal Haze • Epithelial Sloughing or Defects • Striae • Traumatic Flap Dislocation • Diffuse Lamellar Keratitis
    51. 51. LASIK 1 Faster visual recovery – 1 day 2 No Post operative pain 3 Good for low and high myopes 4 Predictable and stable 5 Not good for contact sports LASEK/PRK 1 Visual recovery – 1 week 2 Mild to Moderate post op pain 3 Low myopia, thin corneas 4 Less predictable, modulation 5 Contact sports, military
    52. 52. EPI-LASIK • Surface ablation in which a viable epithelial flap is raised. • The flap is raised at the level of the LAMINA DENSA, the whole basement membrane remains attached to the epithelium, increased survival of basal cells. • Alcohol assited seperation occurs at the level of lamina lucida and reduces survival of the epithelial cells. • ****
    53. 53. CORNEAL RINGSCORNEAL RINGS • In cases like keratoconus structural integrity is increased by : INTACS C3R
    54. 54. INTACSINTACS • Intacs are small semicircular plastics rings of various thickness inserted in the corneal stroma. • They are used for the corrections of 1-3D. • They work by flatting of central portion of the cornea there by correcting myopic refractive error. • They smoothen out corneal irregularities which improves the quality of visison.
    55. 55. CORNEAL COLLAGEN CROSSCORNEAL COLLAGEN CROSS LINKING with RIBOFLAVINLINKING with RIBOFLAVIN • C3R is a procedure which uses RIBOFLAVIN as the photosensitiser with UV rays of 365nm. • UV light increases the number of collagencross linking fibres which are the anchors within the corneal stroma. • RIBOFLAVIN drops are placed every 2 mins, 30 mins prior to UV-A radiation. • After the procedure bandage contact lens is used.
    56. 56. C3RC3R • ADVTG: increase intigrity & progression reduce astigmatism & myopia enhance contact lens fitting C/I : keratometry >60D pachymetry < 400 m infection/ corneal opacity (central) <12 yrs or >40 yrs
    57. 57. Laser thermal keratoplasty • Thermal tissue necrosis gives rise to enhanced corneal remodelling, thereby limiting effect & causing regression. • Ho: YAG laser uses wavelength of 2.13mm ,pulse duration of 200-300ms laser is used to create paracentral corneal coagulation & shrinkage in the controlled manner
    58. 58. • Contact mode : fibr-optic probe to deliver laser pulses to premarked points on the cornea. • NON- Contact mode: A slit lamp delivery system is used to deliver pulses in an octagonal pattern on the cornea simultaneously. Laser thermal keratoplasty
    59. 59. CONDUCTIVE KERATOPLASTYCONDUCTIVE KERATOPLASTY • Utilises radiofrequency energy placed in the periphery of the cornea to cause collagen shrinkage & steepen the central cornea. • 450 x 90 mm2 dimension tip radiofrequency is delivered in the cornea causing thermal effect. • +0.75 – +3.25D correction of cycloplegic refraction with less then -0.75D of astigmatism. • Age >40 yrs
    60. 60. RADIAL KERATOTOMY • Radial incisions were made to modify the surface of the cornea by Sato & his associates in 1894. • To correct myopia, astigmatism & keratoconus. • Radial incisions were made from periphery to the paracentral area . • However it was associted to many complications like posterior extension leading to posterior keratotomy, bullous keratopathy due to several of these complications this procedure is rarely done now
    62. 62. Limbal Relaxing Incisions • Limbal Relaxing Incisions (LRI) are a refractive surgical procedure to correct minor astigmatism in the eye. • Incisions are made at the opposite edges of the cornea, following the curve of the iris, causing a slight flattening in that direction. • They are simpler and less expensive than laser surgery such as LASIK or photorefractive keratectomy.