Intraocular pressure variation associated with body length in young American alligators (Alligator mississippiensis)

C. J. G. Whittaker From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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T. G. Heaton-Jones From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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P. S. Kubilis From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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P. J. Smith From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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D. E. Brooks From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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C. Kosarek From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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E. O. Mackay From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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K. N. Gelatt From the Department of Clinical Sciences (Whittaker, Heaton-Jones, Smith, Brooks, Kosarek, Mackay, Gelatt) and Division of Biostatistics (Kubilis), Health Science Center, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126.

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SUMMARY

Using an applanation tonometer, 5 replicate intraocular pressure (iop) measurements were obtained from each eye of 12 young, clinically normal, American alligators. Alligator length ranged from 46 to 117 cm, measured from snout to tail tip. All iop were recorded by a single observer at an ambient temperature of approximately 25 C, and ranged from 5 to 35 mm of Hg. Observer reliability was excellent (intraclass r = 0.93), and iop did not change over the ordered sequence of 5 replicate measurements/eye. Replicate iop measurements were, therefore, averaged in each eye for comparison between eyes of the same alligator. Left and right eye iop were highly correlated within individual alligators (r = 0.92), whereas the mean within-animal difference between left and right eye iop was not statistically significant (95% confidence interval [ci] for the left eye-right eye mean difference, −1.9 to 1.5 mm of Hg). Mean iop determined for 5 confirmed females and 3 confirmed males did not differ significantly between the sexes (95% ci for the male-female difference in means, −2.1 to 3.7 mm of Hg). Mean ± sem iop of 23.7 + 2.1 mm of Hg determined for 4 alligators < 50 cm long was significantly (P = 0.009) greater than mean iop of 11.6 + 0.5 mm of Hg determined for 8 alligators > 50 cm long (95% ci for the difference in means, 8.5 to 15.7 mm of Hg). In young alligators, the relation between body length and iop appears to be nonlinear, possibly with a negative exponent.

SUMMARY

Using an applanation tonometer, 5 replicate intraocular pressure (iop) measurements were obtained from each eye of 12 young, clinically normal, American alligators. Alligator length ranged from 46 to 117 cm, measured from snout to tail tip. All iop were recorded by a single observer at an ambient temperature of approximately 25 C, and ranged from 5 to 35 mm of Hg. Observer reliability was excellent (intraclass r = 0.93), and iop did not change over the ordered sequence of 5 replicate measurements/eye. Replicate iop measurements were, therefore, averaged in each eye for comparison between eyes of the same alligator. Left and right eye iop were highly correlated within individual alligators (r = 0.92), whereas the mean within-animal difference between left and right eye iop was not statistically significant (95% confidence interval [ci] for the left eye-right eye mean difference, −1.9 to 1.5 mm of Hg). Mean iop determined for 5 confirmed females and 3 confirmed males did not differ significantly between the sexes (95% ci for the male-female difference in means, −2.1 to 3.7 mm of Hg). Mean ± sem iop of 23.7 + 2.1 mm of Hg determined for 4 alligators < 50 cm long was significantly (P = 0.009) greater than mean iop of 11.6 + 0.5 mm of Hg determined for 8 alligators > 50 cm long (95% ci for the difference in means, 8.5 to 15.7 mm of Hg). In young alligators, the relation between body length and iop appears to be nonlinear, possibly with a negative exponent.

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