The causes of Unsatisfactory Unaided visual Acuity after Exximer Laser PRK for Myopia

we analyzed data from 102 patients(152 eyes) who underwent photorefractive keratectomy to investigate the postoperative causes of unsatisfactory unaided visual acuity. A VISX 20/20 exicimer laser(VISX, Inc, Santa Clara, DA USA, version 4. 01) was used in all cases by one surgeon(J.W.H). The patients who showed unsatisfactory unaided vision, less than 20/40 uncorrected visual acuity, with minimal follow-up periods of 6 months were included. A decreased unaided visual acuity was detected in 20 eyes(13%). Range of preoperative myopia was -2.50 to -14.00 diopters. Mean postoperative uncorrected visual acuity(geometric mean)was 0.33+/-0.12 and mean corrected visual acuity was 0.83 +/-0.25. Multiple factors contributed to unsatisfactory unaided vision; myopic regression in 8 eyes, irregular astigmatism in 4 eyes, overcorrection in 1 eye, severe corneal opacity in 1 eyes(2.6%) and the causes were as follows; irregular astigmatism, decentration combined with central island and severe corneal opacity. In conclusion, refractive results after photorefractive keratectomy were reasonably predictable and stable, but some sight threatening complications occured in a minority eyes. Improved techniques such as centering procedures and improved excimer laser program will be essential to prevent unsatisfactory unaided vision.

Prevalence of Central Islands in Corneal Topographic Analysis after Excimer Laser Photo refractive Keratectomy for Myopia

We analyzed the central islands in corneal topography after excimer laser photo refractive keratectomy(VISX Twenty/Twenty B(R) with VisionKey(TM) VISX, Inc. Santa Clara, CA, USA) to evaluate the prevalence of central island and the factors associated with their occurrence, prospectively. Corneal topographic analysis using Corneal Analysis System(EyeSys Technologies, Inc. Houston, TX, USA) was performed in 94 eyes of 77 patients at the postoperative 1-, 3- and 6-months after excimer laser PRK. Central islands were seen in 27%(25/92), 10%(8/79) and 8%(5/64) of patients at postoperative 1-, 3- and 6-months, respectively. There was statistically significant decrease in the occurrence of central island between postoperative 1 and 3 months follow-up groups(p0.05). We found that there was no demonstrable effect of central islands on the decrease of best spectacle corrected visual acuity at postoperative 1 month(p>0.05). Occurrence was statistically significantly decreased in the patients treated with the version 4.01 of central island removal software(1 month: p<0.01, 3 months: p<0.05). We suggest that the version 4.01 software of VISX 20/20B(R) was very effective to reduce the prevalence of central island after excimer laser PRK. In conclusion, if the software would be adjusted to increase the number of pulses centrally, this might reduce the prevalence of central island. New strategies and algorithms might be developed to reduce the prevalence of central islands.