AGE-DIFFERENCES IN CORNEAL HYDRATION CONTROL

  • 1 March 1989
    • journal article
    • research article
    • Vol. 30  (3) , 392-399
Abstract
Dynamic changes in corneal thickness were measured in eight young and eight older normal subjects (mean ages 24.4 .+-. 4.3 years and 71.9 .+-. 7.3 years, respectively) to provide data for quantitative assessment or corneal hydration control and thereby provide information for studying age differences in this important aspect of corneal function. For each subject, pachometry data were obtained by (A) monitoring corneal recovery following hypoxic stress, and by either (B1) measuring recovery after sleep or (B2) by measuring corneal thickness in the late afternoon. The combined data from A and B1 and A and B2 were analyzed through an exponential model to provide information on the: (1) percent recovery per hour (PRPH) following induced corneal hydration; (2) open-eye steady-state (OESS) corneal thickness; (3) residual corneal swelling just before the hypoxic stress test; (4) amount of corneal edema induced by hypoxic stress; and (5) time to reach 95% recovery back to the OESS thickness level (T95%). The results show that between the two age groups, there are substantial differences in some characteristics of corneal hydration while other aspects are similar. For example, the mean PRPH values (58.9 .+-. 7.8% and 34.2 .+-. 6.4%/hr) were significantly higher in the younger subjects (P = 0.0002) and the mean time for 95% recovery to OESS thickness (207 .+-. 42 min and 452 .+-. 117 min) was significantly lower in the younger vs. the older group (P = 0.0002). Also differences between the two age groups were observed at midmorning before starting the hypoxic stress test; the mean corneal thickness of the older subjects was 32.1 .+-. 4.8 .mu.m above the OESS thickness, and this was significantly greater than the results (1.84 .+-. 7.1 .mu.m) found with younger subjects (P = 0.0002). However, the absolute amount of induced corneal swelling following hypoxic stress, 64.2 .+-. 10.6 .mu.m in younger vs. 66.0 .+-. 9.3 .mu.m in older subjects, did not differ significantly (P = 0.96), nor did the mean OESS thickness levels, 516 .+-. 34 .mu.m in younger vs. 537 .+-. 28.9 .mu.m in older subjects (P = 0.234). These results provide strong evidence that corneal hydration control decreases with age. The test methods used in this study show good promise for applicability in the clinical setting so that certain "at risk" patients can be tested and monitored in the ophthalmological office. However, to prove clinically applicable, more work is needed to refine the test procedures to make them as convenient and efficient as possible.

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