Time–Series Changes in the Naturally Hypertensive Monkey Eye

Abstract

Abstract: : Purpose: The Florida colony of naturally ocular hypertensive monkeys (Macaca mulatta) (Dawson et al. BJO 1998) is old enough to begin to provide time–series data. We tested the hypothesis that IOP "spikes" incidence is related to pressure history and optic disc structure and that IOP kinetics vary with pressure history over a span of 20 human equivalent years (HEY). Methods: The 10 semiannual data (IOP and tomography, HRT) samples were organized as, older (> 10 y) or younger (< 7 y) with elevated mean IOP 17–24 mmHg or normal pressure control mean IOP 14–11 mmHg. Eyes were assigned to groups based on 5 year mean IOP at the tenth measurement cycle. IOP spikes were defined as (intermediate of 3 applanation measures) greater than 1 (group) SD (approx. 2 mmHg) above the preceding and subsequent measures. We analyzed spike and non–spike associated data sets. All procedures were approved by the IACUC. Results: IOP spikes were 223% more frequent (p<0.01) in the older elevated IOP eye group (HT) n=12 compared to the older normotensives (ONT) n=18. Spike incidence was not significantly different between ONT, young NT (YNT, n=14) and YHT eye groups n = 5. OHT pressures rose over 20 HEY (p= 0.05). ONT pressures fell (p = 0.028), YHT IOP fell (p =0.028) and YNT pressures did not change significantly. HRT, C/D rose (p =0.016) in the OHT eyes and fell in the ONT eyes (p=0.028) during the period. Conclusions: IOP spikes mask pressure trends by high variance. Significant opposite age–pressure trends were found in old HT and old NT eyes. Shifts in kinetic direction take place around puberty. Extended retrospective analysis is useful for uncovering relations between variables which control HT development in this unique captive sample of natural HT eyes.

Keywords: intraocular pressure • aging • optic disc