Abstract
Purpose: :
To determine if correlations between corneal power, pachymetry and refractive error exist throughout a large heterogeneous group of eyes with a wide range of ametropia.
Methods: :
Retrospective analysis of preoperative data in an excimer surgery database. 3395 eyes from 1858 subjects were included in this study. The spherical equivalent (SE) ranged from 6.75 to -14 D. Refractive error was determined by cycloplegic refraction. Ultrasound was used to measure pachymetry. Keratometry was determined using an autokeratorefractometer.
Results: :
When all the ametropic eyes were analyzed, the SE was observed to be inversely proportional to the mean corneal power (KM) (correlation coefficient, p-value: -.24, <.01) and correlated directly to the corneal thickness (CT) (.07, <.01). The KM and CT were also inversely proportional (-.10, <.01). For just the hyperopes, a correlation between the SE and KM was also found (-.25, <.01) but the CT did not correlate with either of these metrics. For the myopes, an inverse relationship between SE and KM was observed (-.18, <.01). The KM was also found to correlate with the CT (-.11, <.01). A direct correlation was found between KM and the difference in power of the principle meridians (KD) for the ametropic group. This relationship was not observed for the hyperopic group but was found in the myopic group (.08, <.01). Within the myopic group the SE also correlated with the cylinder power (-.04, .04). In all groups, a strong correlation was observed between cylinder power and KD (average correlation coefficient: 0.78, all p-values <.01)
Conclusions: :
By observing correlations within a wide range of ametropia we have found that as the mean refractive error decreases the cornea generally steepens and becomes thinner. As the mean corneal power of myopes increases, the power difference between their principle meridians increases and corresponds to an increase in cylinder. There is a very strong relationship between the power difference in the principle meridians and cylinder refractive error. The confirmation of these relationships could help in the development of eye models and design of new corrective strategies.
Keywords: refractive error development • cornea: clinical science