Abstract
Abstract: :
Purpose: The mouse eye may become an important model to study the genetic control of eye growth and myopia. However, the development of its optical properties has not yet been described. We developed a paraxial schematic eye model for the C57BL/6 mouse for the age range between 22 and 100 days. Methods: Refractive development was recorded with eccentric infrared photorefraction and corneal curvature with infrared photokeratometry. Ocular dimensions were determined in highly magnified videographs of freshly excised eyes which were frozen and cut in a cryostat down to the bisecting horizontal plane (standard deviations were ±10 µm in repeated measurements in several section planes in the same eyes). Inter–eye and inter–individual variability was studied in a total of 20 mice (34 eyes), with 3 to 4 eyes for each of the 9 sampling ages. Schematic eye models were developed using paraxial ray tracing software (OSLO, LT Lambda Research Corporation, and a self–written program). Results: The measured refractive errors started at +4.0 ±0.6 D at approximately 30 days, and levelled off at +7.0 ±2.5 D at about 70 days. Corneal radius of curvature did not change with age (1.414 mm ±0.019 mm). Both axial lens diameter and axial eye length grew linearly (regression equations: lens: 1619 µm + 5.5 µm per day, R=0.916; axial length: 2899 µm + 4.4 µm per day, R=0.936). The lens grew so fast that vitreous chamber depth declined with age (regression equation: 896 µm – 3.2 µm per day, R=O.685). Radii of curvature of the anterior lens surface increased during development (from 0.982 mm at day 22 to 1.208 mm at day 100), whereas the radii of the posterior lens surface remained constant (–1.081 mm ±0.054 mm). The calculated homogeneous lens index increased linearly with age (from 1.568 to 1.605). Retinal image magnification increased from 31 to 34 µm/deg, and the f/number remained ≤ 1 at all ages, suggesting a bright retinal image. A calculated axial eye elongation of 5.4 to 6.5 µm was sufficient to make the schematic eye 1 D more myopic. Conclusions: The most striking features of the mouse eye were that linear growth was slow but extended far beyond sexual maturity, that corneal curvature did not increase, and that the prominent lens growth caused a developmental decline of the vitreous chamber depth.
Keywords: myopia • anatomy • emmetropization