Abstract
Abstract: :
Purpose: . To measure the radius of curvature of the retinal surface at the very center of the foveola, using the adaptive optics scanning laser ophthalmoscope (AOSLO). Methods: The radius of curvature of the foveola was measured in the left eyes of 3 healthy subjects using the radiuscope principle; a technique that was tested and verified with a model eye where the concave surface of a contact lens was used to simulate a foveal pit. Refractive errors of subjects were between –2.00D and +2.00D with no more than 2.00D of astigmatism. One drop each of 1% tropicamide and 2.5% phenylephrine were instilled prior to the experiment to arrest accommodation and to dilate the pupil. In the AOSLO, the aberrations of each individual subject were measured and compensated to improve both lateral and axial resolution of the retinal images. Once aberrations were corrected, a through-focus image series was collected at the center of the fovea for each subject. Movement through focal planes began at a level beyond the photoreceptors and continued anteriorly into the vitreous past the foveal reflex. The enhanced optical sectioning of the AOSLO allowed the foveal surface and its reflex to be distinguished unambiguously. The difference in diopters between the focal plane of the cones and the focal plane of the peak intensity of the foveal reflex was converted into distance, based on a Gullstrand Eye model, to directly yield the radius of curvature in micrometers. Results: The appearance of the foveal reflex varied between subjects. The radius of curvature over the central 50 micrometers of the foveola for the three subjects was found to be 136, 147, and 112 micrometers. One measurement was obtained for the first subject, and two measurements were obtained for the second and third subject. The values were averaged, whenever possible, to find the radius for each subject. Conclusions: The AOSLO provides a unique method of observing the foveal reflex and measuring the radius of curvature of the foveola. This parameter is important since a change in the foveal reflex, whether due to age or disease progression, may be due to a change in the depth or curvature of the foveal pit.
Keywords: macula/fovea • imaging/image analysis: non-clinical • optical properties