Accommodation and spherical aberration

Purpose The accommodation response to changing levels of longitudinal spherical aberration (LSA) was measured. The LSA of the eye is known to change from positive to negative as the level of accommodation of the eye increases. However little is known about the effect of these changes in spherical aberration on the overall accommodation response. Methods The existing monochromatic aberrations of three young subjects were measured using the objective aberroscope procedure across a range of accommodation levels. LSA was induced through the use of aspheric surface, rigid contact lenses (in-air) positioned over a 5mm aperture at a distance of 12mm from the eye. Seven levels of LSA were induced ranging from -3D and +3D of LSA. The subjects viewed a high contrast Maltese cross with the right eye at distances of 33cm and 67cm in photopic conditions. Measurements of accommodation level for each LSA condition were made from the left (occluded) eye using the Canon Autoref R-1, a free-space objective infra-red optometer. Results For the three subjects who were tested, negative LSA caused an increased accommodation response and positive LSA a decreased accommodation response. Pooling the data across subjects and test distances, a linear regression on induced LSA versus accommodation response gave: Accommodation response (D) = 0.23 – 0.25 LSA (D) (r2 = 0.90). Therefore for every 1D of LSA there was approximately 0.25D of accommodation response. Some individual variations occurred and there was some apparent flattening of the slope at the extremes of induced LSA. Conclusions These findings suggest that the accommodation response of the eye will be influenced by the natural changes in spherical aberration of the eye associated with accommodation and by optical corrections of the eye which induce spherical aberration