Tomographic Normal Values for Corneal Elevation and Pachymetry in a Hyperopic Population

Joan T Kim,Michael W Belin,Renato Ambrosio Jr,Michael Cortese,Stephen S Khachikian

doi:10.4172/2155-9570.1000130

Joan T Kim, Michael W Belin + Show 3 more

Open Access

https://doi.org/10.4172/2155-9570.1000130

Copy DOI

Abstract

Purpose: To establish a normative data base with respect to corneal pachymetry and elevation tomography appropriate for refractive surgery screening of hyperopic individuals. Methods: 100 eyes of 51 consecutive hyperopic patients were examined with the Oculus Pentacam HR to determine corneal pachymetry and anterior and posterior elevation values at the apex and thinnest point. All patients were otherwise screened as normal and all principal meridians were hyperopic. Results were compared to a previously studied data base of myopic individuals from the same practice. Results: The average corneal thickness at the apex and thinnest point was not significantly different between the hyperopic and myopic groups (P>0.05 at both locations). The mean anterior elevation at the apex was0.4 ± 1.9 µm in the hyperopic group vs. 1.6 ± 1.3 µm in the myopic group (P<0.001). The mean anterior elevation at the thinnest point was-0.1 ± 2.2 µm in the hyperopic group vs. 1.7 ± 2.0 µm in the myopic group (P<0.001). The mean posterior elevation at the apex was5.7 ± 3.6 µm in the hyperopic group vs. 0.8 ± 3.0 µm in the myopic group (P<0.001). The mean posterior elevation at the thinnest point was10.6 ± 5.7 µm for the hyperopic group vs. 3.6 ± 4.1 µm for the myopic group (P<0.001). When adjusted for age, the posterior elevation changes remained statistically significant. Conclusions: Hyperopic individuals exhibited greater variation in posterior tomographic elevation values than a comparable myopic group. Currently used data bases need to be adjusted for screening hyperopic individuals to reduce the number of false positives associated with using a myopic biased data set.

Highlights

An increasing percentage of the estimated one million people in the United States who undergo refractive surgery annually, are hyperopic
Most topographic pre-surgical screening normal values have been based on a predominantly myopic population [1,2]. This is mainly due to the fact that, in the past, the vast majority of individuals undergoing refractive surgery were myopic, and published normal values often reflected the propensity of myopes in the early study populations
Hyperopic eyes are associated with a shallower anterior chamber [3], increased incidence of narrow angle glaucoma [4], shorter axial length, higher sphericity, and higher total and corneal spherical aberration compared to myopic eyes [5]

Summary

Introduction

An increasing percentage of the estimated one million people in the United States who undergo refractive surgery annually, are hyperopic. Most topographic pre-surgical screening normal values have been based on a predominantly myopic population [1,2] This is mainly due to the fact that, in the past, the vast majority of individuals undergoing refractive surgery were myopic, and published normal values often reflected the propensity of myopes in the early study populations. It was unknown; whether these myopic biased values were applicable to a hyperopic population.It is well-established that the myopic and hyperopic populations are diverse. Specific population-based normal values can have important clinical implications

Methods

Results

Conclusion