The Influence of Age on Multiple Anatomic and Biomechanical Ocular Parameters in the Normal Healthy Eye

Abstract

Purpose:: To evaluate the anatomical and biomechanical changes that occur in the normal eye with age.

Methods:: 86 subjects (ages 20-88) were recruited for this study into the following decade groups: 20’s (n=20), 30’s (n=16), 40’s (n=17), 50’s (n=17), 60+ (n=16). Subjects with any previous eye surgery, eye disease, or a history of diabetes were excluded.One eye of each subject was measured with the Ocular Response Analyzer (ORA), IOL Master, Pach Pen, Schiotz tonometer, Dynamic Contour Tonometer (DCT), Goldmann Applanation Tonometer (GAT), Optical Coherence Tomographer (OCT), and the Heidelberg Retinal Tomograph II (HRT II). All non-contact measurements were taken prior to topical anesthesia and acquisition of contact measurements. Univariate regression analysis was performed to determine statistically significant relationships between measured parameters and age.

Results:: GAT IOP increased significantly with age (p=<.0001, r²=.1725), however, DCT IOP (p= .675) and ORA IOPcc (p=.154) showed no significant relationship with age. Analysis of the various components of the ORA signal showed Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF) to have no significant relationship with age, while the "in" applanation peak of the ORA signal did increase with age (p=.0019, r²=.1033). RNFL average thickness measured by the OCT decreased significantly with age (p=<.0001, r²=.3625). HRT analysis showed a significant decrease with age in several global parameters: rim area (p=.0206, r²=.0516), rim volume (p=.0049, r²=.0805), height variation contour (p=.0071, r²=.0731), and mean RNFL thickness (p= .0004, r²=.1300). Central Corneal Thickness (CCT) did not increase significantly with age (p=.1784).

Conclusions:: DCT IOP and ORA IOPcc are pressure measurements that are less sensitive to corneal properties than other methods such as traditional GAT. The fact that neither DCT IOP nor ORA IOPcc showed a significant increase with age while GAT IOP did, suggests that "true" IOP is not increasing with age, but that the artifactual GAT increase is due to a change in corneal properties with age. As CCT was shown to have no relationship with age, the increase in GAT cannot be attributed to increasing corneal thickness. The significant increase in the "in" signal peak value suggests that corneal properties change with age in a manner not detected with CH and CRF. The decrease in RNFL thickness and other optic disk parameters that occur with age are not attributable to increasing IOP with age.

Keywords: aging • intraocular pressure • clinical (human) or epidemiologic studies: natural history