Laser EYE SURGERY LASIK and Excimer Lasers Michael Hutchins The PROBLEM opia - near sightedness used by either an elongated or steep cornera. focal point is in front of the na instead of on it. ically corrected with concave THE PROBLEM eropia - far sightedness sed by a flat cornea or ort eye. al point is behind the na. rected with concave es (positive optical THE PROBLEM gmatism arises from different focal points in different nes of the eye. used by non-uniform curvature of the cornea or scarrin lens. gular astigmatism cannot be fixed by glasses, just conta INTERNAL CORRECTIONS SIK - Laser Assisted in SItu Keratomileusis atomileusis is the procedure of opening the eye and ring the cornea. SIK uses an excimer laser to perform the alterations an er a knife or a femtosecond laser to create the openin SIK is an alternative to wearing glasses or contacts as it LASIK SIK began in 1950 in Bogotá, Columbia with the elopment of keratomileusis. reakthrough was the 1973 announcement of the excim r. Gholam Peyman filed the first LASIK patent in 1989 a ethod for modifying corneal curvature”. It includes the cedure of revealing the cornea, using an excimer laser LASIK ASIK is performed while awake th an occasional mild sedative. hinged flap is cut with either a etal blade or a femtosecond ser. n Excimer laser remodels the ornea by ablating tissue. he flap is repositioned and left LASIK ting the flap is either done with a microkeratome or a tosecond laser. Excimer Lasers mer lasers are UV lasers that utilize le gas halides. y often use a combination of an inert such as argon, krypton or xenon h a highly reactive gas like chlorine or rine. hort lived molecule called an excimer Excimer Lasers mers are formed en the inert gas s into an excited e, in this state they d with the halide orm a molecule. Excimer Lasers en the noble gas urns to its ground e it repels the halide ch gives rise to the aviolet light. EXCIMER LASERS cal wavelengths for ous excimers. bond energy of an H-O d of H2O is about 4.76 and to break a C-H bond thane it is 4.38 eV ble light is 2-3 eV while Excimer Wavelength (nm) Ar2* 126 Kr2* 146 F2 157 Xe2* 172 & 175 ArF 193 KrF 248 XeBr 282 XeCl 308 XeF 351 CaF2 193 KrCl 222 Cl2 259 Energy (e 9.85 8.50 7.90 7.21 & 7.0 6.43 5.00 4.40 4.03 3.54 6.43 5.59 4.79 Excimer Lasers ultraviolet light is absorbed by tissue and organic matte added energy breaks the bonds of molecules at the sur se molecules ablate into the air without adding heat to a. This is called Ablative Photodecomposition. rent excimer lasers typically pulse for 10 ns at 100 Hz. se used in eye surgery reposition to follow the eye 400 es per second. Excimer Lasers low absorption depth: 0.1 •  Discharge circuit - expen 0.5µm. and require frequent maintenanceLaser gas mix rgy highly absorbed by is toxic and corrosive. erials. form power density over tively large area. •  The laser must be refilled fresh gas regularly. LASIK Side Effects ome higher order abberations can ccur as they cannot be diagnosed th normal eye exams. ne is halos and starbursts: vision fine during the day but at night e pupil can expand and pass the dge of the LASIK flap, this gives e to halos and other abberations. Surgery induced dry eyes Over or under correction Visual acuity fluctuation Halos or starbursts around sources at night Light sensitivity Ghost images Wrinkles in flap Decentered ablation Debris or growth under fl Induced astigmatism Corneal Ectasia Floaters Epitheliun erosion LASIK Alternatives SIK is limited by the excimer laser and can cause some mage to the eyes nerves so new methods are being eloped. other popular method is PRK it is similar to LASIK with essitating a flap to be cut (necessary for pilots). mpared to LASIK it has a longer recovery period and m omfort. References kipedia entries on: LASIK, Excimer Laser, Excimer, Myo peropia, Astigmatism (eye), Keratomileusis, Photorefrac atectomy n-Wikipedia images from: p://eyeclinicpc.com/lasik/lasik.htm and http:// w.nseyespecialists.com/images_content/technolasphot