Evidence for Delayed Presbyopia after Photorefractive Keratectomy for Myopia
Received 20 April 2005; accepted 24 January 2006.
Purpose
To evaluate uncorrected near visual acuity (NVA), accommodation, corneal aberrations, and the optical quality of the retinal image in presbyopic eyes after photorefractive keratectomy (PRK).
Design
Nonrandomized comparative retrospective study.
Participants
Ten post-PRK patients and 10 normal patients.
Methods
Twenty eyes (10 right and 10 left after PRK for myopia, minimum of 10 years after the operation; group A) were compared with 20 eyes (10 right and 10 left age- and gender-matched normal controls; group B). All subjects were over 40 years of age.
Main Outcome Measures
With best distance correction, NVA was measured at 40 cm (Jaeger, J series), and the range of accommodation (diopters [D]) was measured subjectively (negative relative amplitude and positive relative amplitude). The modulation transfer function (MTF) and corneal aberrations such as comalike, spherical (SAs), and higher order (HOAs) were measured with a Hartmann–Shack aberrometer. From the MTF curves, the spatial frequencies corresponding to contrast values of 0.1 and 0.5 were noted.
Results
Mean ages (± standard deviations [SDs]) were 46.3 years (4.7) for group A and 47.6 years (4.9) for group B (P>0.05). Near acuity was J1 or better in 12 of 20 post-PRK and 4 of 20 control eyes. Mean accommodations (± SDs) were 3.2 D (1.14) for right group A eyes and 2.1 D (0.94) for right group B eyes (P = 0.0152), and 3.4 D (0.99) for left A eyes and 2.3 D (1.02) for left B eyes (P = 0.0168). Total HOA indexes (± SDs) were 1.449 (0.409) for right group A eyes and 0.824 (0.241) for right group B eyes (P = 0.008), and 1.464 (0.388) for left A eyes and 1.067 (0.542) for left B eyes (P = 0.0752). Pooling the data from post-PRK and control eyes, a significant correlation was found between near acuity and SA (right eyes, r = −0.535, P = 0.015; left eyes, r = −0.493, P = 0.027). Significant associations were found between accommodation, near acuity, HOA, and comalike aberration for right eyes only. Mean spatial frequencies (± SDs) corresponding to contrast values of 0.1 for right and left eyes were 14.96 (5.71) for right group A eyes and 22.02 (6.85) for right group B eyes (P = 0.074), and 15.11 (7.80) for left A eyes and 21.41 (9.00) for left B eyes (P = 0.271). Mean spatial frequencies (± SDs) corresponding to contrast values of 0.5 for right and left eyes were 2.86 (0.63) for right group A eyes and 3.21 (0.35) for right group B eyes (P = 0.596), and 2.76 (0.98) for left A eyes and 3.22 (0.27) for left B eyes (P = 0.194).
Conclusions
Compared with normal eyes, in previously myopic eyes treated with first-generation PRK lasers there is a tendency for (1) the optical quality of the retinal image to be reduced at low contrast, (2) the aberrations attributed to the corneal surface to increase, and (3) both measured subjective accommodation and near acuity to be greater than expected. We postulate that the corneal aberrations induced by PRK for myopia may reduce the quality of the retinal image for distance but enhance near acuity by way of a multifocal effect that can delay the onset of age-related near vision symptoms.
Research, Development, and Innovation Department, Vissum, Institute of Ophthalmology and School of Medicine, University Miguel Hernández, Alicante, Spain
Correspondence to Jorge L. Alió, MD, PhD, Research, Development, and Innovation Department, Vissum, Instituto Oftalmológico de Alicante, Avda. Denia s/n, Edificio Vissum, 03016, Alicante, Spain
Manuscript no. 2005-342.
The authors have no proprietary interest in any of the materials or methods described herein.
This study has been supported in part by a grant from the Spanish Ministry of Health, Instituto de Salud Carlos III, Red Temática de Investigación en Oftalmología, Subproyecto de Cirugía Refractiva y Calidad Visual, Madrid, Spain (reference no.: CO3/13), and by a grant from the Spanish Generalitat Valenciana (ref.: Grupos05/036 Grants and Support for scientific research and technological development in the Comunidad Valenciana for the year 2005).
ABSTRACT