Lasik Myopia

LASIK Myopia Author: Michael Taravella, MD; Chief Editor: Hampton Roy Sr, MDBac!round"ne of the mo#t promi#in! and e$citin! development# in the %orld of refractive #ur!ery ha# &een the advent of la#er in #itu eratomileu#i# '(AS)*+, The #ur!ical techni-ue involve# the creation of a hin!ed lamellar corneal flap, after %hich an e$cimer la#er i# u#ed to mae a refractive cut on the underlyin! #tromal &ed, (AS)* i# a fu#ion of old and ne% technolo!ie#, %ithit# root# in eratomileu#i# and automated lamellar eratectomy 'A(*+, Ho%ever, a# currently practiced, it i# perhap# &e#t thou!ht of a# photorefractive eratectomy '.R*+ performed under aflap in#tead of on the corneal #urface,(AS)* ha# &een availa&le in the /nited State# a# an off0la&el procedure #ince the mid 1223#, 4DA approval of e$cimer la#er# for (AS)* date# to a&out 1222,516Many million# of procedure# have &een performed %orld%ide, Accordin! to the American Society of Cataract and Refractive Sur!ery, a&out 733,333 procedure# a year are currently performed in the /nited State#,Spherical a&erration: a #chematic dia!ram for the human eye,Hi#tory of the .rocedure8o#e Barra-uer i# !enerally credited %ith much of the early %or leadin! to corneal lamellar refractive procedure# a# they are currently practiced, He noted that refractive chan!e could &e accompli#hed in the cornea &y ti##ue addition or #u&traction, He #ue-uently developed the idea of re#ectin! a corneal di#c and free9in! it, follo%ed &y #hapin! the di#c %ith a cryolathe,5:, ;, # ori!inal %or involved performin! a corrective e$cimer la#er a&lation on the &ac of a re#ected di#c of corneal ti##ue, Thi# di#c %a# replaced and #utured onto the cornea, .alliari# developed the techni-ue of performin! the e$cimer la#er corrective a&lation inthe corneal #tromal &ed under a hin!ed flap, He fir#t #tudied the procedure in ra&&it#, follo%ed &y &lind human eye# in 12=2, and then #i!hted eye# in 1221,)n 122;, Steve Slade added the refinement of u#in! an automated microeratome to create the flap and %a# one of the fir#t /S #ur!eon# to perform (AS)*,)ndication#A# of Decem&er :33=, (AS)* ha# &een approved &y the 4ood and Dru! Admini#tration '4DA+ for #everal different la#er platform#, includin! the ?)S@ STAR S# vi#ion %ill &lac out momentarily, )ntraocular pre##ure %ith the #uction rin! applied i# &et%een G3023 mm H!, Hi!h pre##ure i# nece##ary to hold the #uction rin! firmly in place and to properly e$po#e the cornea to the cuttin! mechani#m of the microeratome,A depth plate in the microeratome determine# the planned thicne## for the flap re#ection '1;3 Dm for the Moria "ne /#e .lu#+, Ho%ever, thi# repre#ent# only an e#timate of the actual flap thicne##; confirmation %ith on0the0ta&le pachymetry mea#urement# taen immediately &efore cuttin! the flap 'total corneal thicne##+ and in the #tromal &ed after the flap ha# &een lifted 're#idual #tromal &ed+ i# the &e#t %ay to determine actual flap thicne##,"nce !ood #uction i# confirmed, a foot pedal i# u#ed to #imultaneou#ly #%itch on the motori9ed vi&ratin! &lade that cut# the corneal flap and the mechani#m that advance# the microeratome, The microeratome #hould not &e manipulated durin! the flap cuttin! pha#e, and it i# important to remind the patient not to move or attempt to #-uee9e the eye #hut durin! the cut, The hin!e %idth can &e #et on thi# microeratome &y #ettin! a #top on the #uction rin!, The #top #ettin! i# &a#ed on a nomo!ram #upplied &y the manufacturer and i# &a#ed on the #i9e of the openin! of the #uction rin! and corneal curvature eratometry readin!#,Femtosecond laser flap creationThe procedure i# different if a femto#econd la#er i# u#ed to create the flap, 4emto#econd la#er# emit in the infrared ran!e '13C; nm %avelen!th+ and %or &y creatin! overlappin! microcavitation &u&&le#, producin! a lamellar intra#tromal cut, The la#er i# fir#t pro!rammed to confirm the de#ired depth, diameter, and hin!e location of the flap, The la#er then mu#t &e IdocedI to the patient># eye to hold the eye completely immo&ile durin! la#er emi##ion, The la#er i# then fired, creatin! the potential lamellar #pace fir#t follo%ed &y a #ide cut to connect theflap to the #urface of the cornea,"ne of the !reat advanta!e# of the femto#econd la#er for flap creation '#uch a# the )ntrala#e, AM"+ i# the a&ility to cu#tomi9e diameter and hin!e location; thi# i# e#pecially u#eful for hyperopic a&lation# and treatment# for mi$ed a#ti!mati#m, %hich re-uire lar!er a&lation 9one#, A #maller #tromal &ed %ould mean that the planned e$cimer la#er treatment %ould overlap uncut cornea, potentially re#ultin! in an incomplete or partial a&lation and correction of the de#ired refractive error,Microeratome0created flap# depend on corneal curvature mea#urement#, that i#, the #teeper the cornea, the more cornea that i# e$po#ed to the microeratome durin! the for%ard pa##, re#ultin! in a lar!er diameter flap, The flatter the cornea curvature, the #maller the flap diameter,?ery #teep cornea# 'J# Eye and ?i#ion Center, Al#o, #ee eMedicineHealth># patient education article ?i#ion Correction Sur!ery,Complication#Complication# can &e divided into intraoperative 'u#ually microeratome related+ and tho#e that occur po#toperatively,512, :3, :16 The follo%in! li#t outline# the more common complication#, the time period in %hich they are liely to &e #een 'ie, immediate, early po#toperative, late po#toperative+, and an appro$imate incidence of occurrence, Each complication %ill &e di#cu##ed in more detail in the follo%in! #ection,)ntraoperative microeratome flap complication# include the follo%in!: Entry into eye 'intraoperative; rare+ 5::6 Thin, irre!ular, or perforated flap 'intraoperative; K 3,:E+ 5:;6 4ree flap 'intraoperative; rare; 3,:E+4emto#econd la#er flap complication# are a# follo%#: "pa-ue &u&&le layer ?ertical !a# &reathrou!h Anterior cham&er !a# &u&&le# Suction lo## durin! flap creation(a#er0related complication# include the follo%in!: Decentration 'K 1E+ )rre!ular a#ti!mati#m 'K 1E+ and central i#land#"ther po#toperative complication# include the follo%in!: ?i#ually #i!nificant %rinle# or #triae in the flap '1E+ Di#located flap 'early po#toperative period+ )nfection 'early po#toperative period; very rare; K 3,3:E+ 5: