Accommodation and spherical aberration

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