Effects of Ablation Diameter on Long-term Refractive Stability and Corneal Transparency after Photorefractive Keratectomy
Presented at: American Academy of Ophthalmology Annual Meeting, November 2003, Anaheim, California.
Received 13 November 2005; accepted 12 June 2006.
Objective
To evaluate the effects of ablation diameter on long-term refractive stability and corneal transparency after photorefractive keratectomy (PRK).
Design
Long-term, prospective, follow-up study.
Participants
One hundred twenty-three eyes treated between 1990 and 1993 at one institution as part of a number of ethical committee–approved clinical studies underwent long-term follow-up at 10 to 12 years after PRK.
Intervention
Photorefractive keratectomy was performed using the Summit Technology UV 200 and OmniMed Excimer lasers with either 4.0-mm (n = 36), 5.0-mm (n = 47), or 6.0-mm (n = 40) optical zones and either −3.0-diopters (D) or −6.0-D myopic spherical corrections, based on the original Munnerlyn algorithms.
Main Outcome Measures
Refractive stability, refractive predictability, best spectacle-corrected visual acuity, and corneal haze.
Results
Refractive outcome at 1 and 10 to 12 years of follow-up was better with 6.0-mm treatments, especially for −6.0-D corrections (P>0.001). The early hyperopic shift was significantly reduced with 6.0-mm zones, with less regression between 1 and 6 months, compared with 5.0- and 4.00-mm PRK, especially for −6.0-D corrections (P<0.001). The postoperative refraction remained stable between 1 and 10 to 12 years in all groups. Objective measurements of haze were less with 6.0-mm compared with 4.0- and 5.0-mm treatments (P<0.001). Night vision problems were significantly less with 6.0-mm PRK (P<0.01). There was no evidence of progressive hyperopic shift, corneal ectasia, or late onset of corneal haze in any of the eyes during the follow-up period.
Conclusions
Refractive stability was maintained between 1 year and 10 to 12 years after PRK with 4.0-, 5.0-, and 6.0-mm optical zones. A significant linear trend was observed in terms of refractive predictability, early hyperopic shift, regression, corneal transparency, and night haloes with better outcomes in PRK with a larger ablation zone. None of the eyes had sight-threatening complications such as ectasia or late-onset corneal haze during the follow-up.
Department of Academic Ophthalmology, St. Thomas’ Hospital, London, United Kingdom.
Correspondence to Madhavan S. Rajan, MRCOphth, FRCS, Department of Academic Ophthalmology, Rayne Institute, St. Thomas’ Hospital, London SE1 7EH, United Kingdom.
Manuscript no. 2005-1103.
Supported by the Iris Fund for the Prevention of Blindness, London, United Kingdom.
The authors have no financial interests related to the article.
ABSTRACT