Postnatal refractive development in the Brown Norway rat: Limitations of standard refractive and ocular component dimension measurement techniques

Purpose. The genetic tractability of the rat and its larger eye size as compared to the mouse make it an attractive model for studies of ocular development and emmetropisation. This study aimed to provide normative data in the strain of rat being used for the rat genome sequencing project whilst also evaluating standard measurement techniques. Methods. Ocular refraction (retinoscopy. Hartinger coincidence optometry) and ocular component dimensions (keratometry, A-scan ultrasonography, calliper measures, eye weight) were measured at intervals from eye-opening to adulthood. Results. There was no convincing evidence of visually guided emmetropisation during normal development. Key measurement techniques such as high-resolution A-scan ultrasonooraphy, which work effectively in several other animal species, were unusable or inaccurate in the rat. Conclusions. This study found no evidence of emmetropisation during normal development in rat. As in mice, technical difficulties prevent accurate measurement of ocular refraction and vitreous chamber depth and may complicate tests of emmetropisation to imposed blur.