The cornea and corneal endothelium in the aged rabbit

The rabbit is commonly used in corneal research yet few data are available concerning the impact of age, especially on the morphology of the corneal endothelium. An exploratory study was undertaken to assess corneal dimensions and thickness and endothelial cell density (ECD) as a function of age. Female New Zealand White (NZW) rabbits were individually housed in diet-, temperature-, humidity-, and light-controlled conditions for up to 3 years. Body weight increased from 1 kg at 6 weeks to 6 kg at 3 years. Horizontal corneal diameter increased from 11.34 mm at 6 weeks to 16.75 mm at 3 years, whereas corneal thickness increased from 300 to 465 microns over the same time period. ECD decreased from approximately 4100 cells/mm2 to less than 3000 cells/mm2 by 6 months and to less than 2000 cells/mm2 by 2 years. Scanning electron microscopy (SEM) evaluations revealed that mild endothelial polymegethism, as assessed by regional variance in the endothelial mosaic, was likely to be detectable by 9 to 12 months. For the use of the rabbit in studies of the aged cornea, a minimum age of 9 months (i.e., approximately 4.25 kg in weight) is therefore recommended.