Smoothness of ablation on polymethylmethacrylate plates with four scanning excimer lasers.
OBJECTIVE
To perform a quantitative evaluation of smoothness of ablation on polymethylmethacrylate (PMMA) using four scanning excimer lasers available commercially for photorefractive surgery.


METHODS
Ablations were done on PMMA plates with dimensions 100 x 50 x 1 mm. Four scanning excimer lasers were used, two with flying spot technology (Zeiss-Meditec MEL-70, and a Russian-made unit, Microscan) and two Nidek models with scanning slit delivery systems and an expanding iris diaphragm (EC-5000 and EC-5000 CX). Forty PMMA plates were ablated with standard -3.00-D settings using an ablation zone of 6 mm; each laser ablated 10 plates. Measurements were made in the center of each plate with the Zygo microscope, based on the principle of white light interferometry. Smoothness of ablation was characterized by three surface parameters (RMS, Ra, PV). RMS was considered the most significant parameter.


RESULTS
The smoothest surface was obtained in samples produced by Zeiss-Meditec MEL-70 unit (RMS=112 +/- 23 nm), followed by the Nidek EC-5000 CX (RMS=153 +/- 12 nm), and the Microscan (RMS=181 +/- 11 nm). The smoothness of ablation produced by the Nidek EC-5000 unit (RMS=329 +/- 39 nm) was significantly less than the other three lasers (P<.01).


CONCLUSIONS
Scanning excimer lasers based on flying spot technology--Zeiss-Meditec MEL-70 and Microscan, as well as the Nidek EC-5000 CX with FlexScan--created smoother ablations on PMMA plates compared to the older Nidek EC-5000 unit.
Doga
Alexander V
AV
State Institution Intersectoral Research and Technology Complex Eye Microsurgery named after Prof Svyatoslav N. Fyodorov, Moscow, Russia. alexander_doga@hotmail.com
Shpak
Alexander A
AA
Sugrobov
Victor A
VA
D003315:Cornea; D006801:Humans; D054018:Lasers, Excimer; D008953:Models, Anatomic; D018903:Photorefractive Keratectomy / Q000592:standards*; D019904:Polymethyl Methacrylate; D013499:Surface Properties
D019904:Polymethyl Methacrylate