Interpreting the Distortion Associated with a Retinal Wholemount

Wholemounting is a standard procedure used to view the retinal organization in light microscopic studies. Radial cuts are made into the retina from its perimeter to allow it to be flattened onto a glass slide. This process distorts the retina and introduces missing pie (phantom) sectors into the wholemount. Distortion in the retinal wholemount has been quantified by modeling the retina as a hemisphere transformed into a disc interrupted with phantom sectors. The interrupted continuity of the retinal wholemount indicates that an angle subtended at the center of the wholemount must be smaller than its corresponding angle in the intact retina. In the model presented here (H–D transform) a method is described for interconverting angles between the hemisphere and the wholemount and for transforming any point on the wholemount back onto the surface of the hemisphere. Computations on the model show that the angles, subtended by phantom sectors at the center of a wholemounted retina, on a given concentric circle can be quantified and summed to a constant value. The value depends on and monotonically increases with eccentricity, it is nil at the center of the wholemount and maximal at the retinal margin. As a result, radial cuts made in the periphery of the wholemount need not extend into its center. In addition, sector edges of the wholemount are approximated by quarter wave sinusoids, larger sectors having greater amplitude and consequently greater distortion. Moreover, a large piece of tissue exerts more spring recoil and thus in large retinas relatively more cuts are required in the wholemount. However, the total angle deficit of the phantom sectors around the circumference of the wholemount is unaffected by the radius of the eye. A standard configuration for the wholemount is defined that minimizes the overall error in orientation for any sector.