Presbyopia after Keratectomy

Abstract

It is with great interest that we read the recent article by Artola et al.1Artola A. Patel S. Schimchak P. et al.Evidence of delayed presbyopia after photorefractive keratectomy for myopia.Ophthalmology. 2006; 113: 735-741Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar The authors found that the subjective accommodation of post–photorefractive keratectomy (PRK) patients was statistically significantly higher than that of the controls; both matched for age and gender. The average age of subjects in the study group was a year less than the controls (46.3 and 47.6), though not statistically different. In addition, the better uncorrected near vision was associated with reduced distance vision in the study group, suggesting residual myopia. The authors concluded that the delayed onset of presbyopia and improved uncorrected near acuity in post-PRK patients is because of the pseudoaccommodative effect resulting from an increase in the corneal spherical aberration and depth of field after PRK. There have been suggestions in the literature that corneal aberrations after radial keratotomy too could delay presbyopic symptoms by increasing the depth of field.2Hemenger R.P. Tomlinson A. McDonnell P.J. Explanation for good visual acuity in uncorrected hyperopia and presbyopia after radial keratotomy.Invest Ophthalmol Vis Sci. 1990; 31: 1644-1646PubMed Google Scholar Although it may be possible that corneal aberration could delay presbyopic symptoms, a more likely explanation for the delay in onset of presbyopic symptoms in myopes is the inherent larger amplitude of accommodation (AA) in myopes compared with hypermetropes or emmetropes. In a study on the AA and refractive errors in young subjects, McBrien and Millodot3McBrien M.A. Millodot M. Amplitude of accommodation and refractive error.Invest Ophthalmol Vis Sci. 1986; 27: 1187-1190PubMed Google Scholar found that the AA in myopes is greater than that in emmetropes or hypermetropes. They found that in the 80 subjects studied the AA was highest in late-onset myopes, followed by early-onset myopes, emmetropes, and hypermetropes. In our study4Abraham L.M. Kuriakose T. Sivanandam V. et al.Amplitude of accommodation and its relation to refractive errors.Indian J Ophthalmol. 2005; 53: 105-108Crossref PubMed Scopus (31) Google Scholar of 316 patients in the peri-presbyopic age group (35–50 years) including 50 myopes, we found that the AA in myopes was statistically significantly higher than those in emmetropes and hypermetropes up to age 45. After that age, the AA seemed to converge to similar values in the 3 refractive groups. These studies show an inherent increase in AA in myopes compared with other refractive groups. The post-PRK patients in the present study possibly had moderate to high myopia and a correspondingly high AA. This preserved accommodation could be the reason for delayed presbyopia. The residual myopia and slightly younger age of the study group would have further affected the findings. Author ReplyOphthalmologyVol. 114Issue 4PreviewWe are grateful to Drs Abraham and Kuriakose for their interest, attention to detail, and time spent on commenting on our article, in which we reported that subjective accommodation was 1.1 diopters (D) greater after photorefractive keratectomy (PRK) compared with normals. However, we do not think McBrien and Millodot’s report1 is completely relevant with respect to our study because their work was based on a population with an average age less than half that of our subjects. The amplitude of accommodation may be greater in myopes younger than 20 years than in emmetropes. Full-Text PDF