Longitudinal intraocular pressure measurements in Whooping cranes (Grus americana) and Mississippi-Sandhill cranes (Grus canadensis pulla)

Objective: To assess intraocular pressure (IOP) development in cranes and determine the impact of age, weight, species, head position, and sex.Animals Studied: Whooping cranes (WC) (Grus americana), and Mississippi-sandhill cranes (MSC) (Grus canadensis pulla).Procedures: Chicks were manually restrained on days 1-3, 7, 21, 35, 60, 75, and 120 for routine examinations. IOP was opportunistically measured utilizing the Tonovet Plus (R) in D setting with the head above the heart (AH) and below the heart (BH). Values were also obtained longitudinally in adults (>120 days old) upon presentation in 1 year.Results: Intraocular pressure was highly correlated with age and weight in chicks. For every kilogram gained, IOP increased 2.46 +/- 0.08 mmHg in WC and 2.66 +/- 0.11 mmHg in MSC. Once hatched, IOP increased 1.13 +/- 0.04 mmHg in WC and 0.87 +/- 0.04 mmHg in MSC every 10 days. IOP was similar to adults at 120 days of age. In adult WC, mean IOP AH was 24.0 +/- 0.4 mmHg, and BH was 27.9 +/- 0.4 mmHg, there was a significant difference regarding head positioning and sex, females (25.3 +/- 0.4 mm Hg) had lower IOP than males (26.5 +/- 0.4 mmHg). In adult MSC, mean IOP AH was 20.7 +/- 0.4 mmHg, and BH was 24.6 +/- 0.4 mmHg. The difference between head positioning was significant.Conclusions: This study documents the correlation between IOP and weight or age during early development in cranes, as well as the importance of head positioning.