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C. J. Roberts, J. D. Peterson, A. M. Mahmoud, P. A. Weber; The Influence of Age on Anatomic and Biomechanical Ocular Parameters in "Stiffer" and "Softer" Normal Healthy Eyes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2045.
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To evaluate the anatomical and biomechanical changes that occur with age, as a function of a corneal stiffness parameter.
84 subjects were prospectively recruited (age range: 20 to 88 years). Subjects with 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). Non-contact measurements were taken prior to topical anesthesia and contact measurements. Eyes were divided into 2 groups based on the sign of the calculated "GAT error" parameter, defined as GAT minus DCT, with positive error denoting "stiffer" eyes (n = 53) and negative error denoting "softer" eyes (n=31). Univariate regression analysis was performed between measured parameters and age in each group. Also, t tests were performed between groups on all parameters measured.
The following parameters were significantly different between groups (p =< 0.01): age, GAT, and the height of the first infrared signal peak of the ORA, Peak 1, with all three parameters greater in the stiffer eyes. GAT increased significantly with age only in the stiffer eyes (p<0.004, r2=.1345). Softer eyes had no significant relationship (p= 0.498). There was no significant group relationship with age using DCT or ORA. RNFL average thickness measured by the OCT decreased significantly with age only in the stiffer eyes (p<0.0001, r2=0.4555). RNFL thickness measured by HRT II analysis showed a significant decrease with age only in the stiffer eyes in RNFLg (p<0.0085, r2=.1112), RNFLts (p<0.0084, r2=.1112), RNFLn (p<0.0117, r2 =.1010), and RNFLns (p<0.0042, r2=.1328). No significant relationship with age was found in RNFLt, RNIFti, and RNFLni in either group. Central Corneal Thickness did not increase significantly with age (p=.1784), and was not different between groups (p=0.3660).
Eyes with "stiffer" corneas age differently than eyes with "softer" corneas. Stiffer corneas are associated with increasing corneal stiffness and decreasing RNFL thickness. The increase in GAT with age in the "stiffer" group may be attributed to increasing stiffness rather than increasing IOP, which is further supported by the increase in Peak 1 with age. Thus, the decrease in RNFL thickness that occurs with age is not correlated to increasing IOP with age, but rather increasing corneal stiffness.
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