|Title||WHERE IS THE LAG OF ACCOMMODATION IN THE DEPTH OF FIELD?|
|Author, Co-Author||Heather Johns, Von Pham, Ruth E. Manny, Ying-Sheng Hu|
|Abstract|| PURPOSE: When presented with a near target the eye's accommodative response typically does not match the demand but lags behind the target. The target appears clear due to a range around the target where blur is not detected, the depth of field (DOF). The expectation is that the lag should fall within the DOF and the magnitude of the lag and DOF should be related. This study investigated the relationship between DOF and lag of accommodation.
METHODS: Monocular DOF and lag were investigated at 2, 3, 4 and 6D accommodative demands. DOF measures were modeled after Campbell (1957) with the subject positioned in a chin and forehead rest viewing a set of 5 dots printed on transparent plastic. Three dots aligned vertically served as the accommodative target. The viewing distance was changed in random order to modify the accommodative demand. The size of the 3 dots varied with accommodative demand to maintain a 10min of arc subtense at the eye. The other 2 dots printed on 2 separate transparencies were positioned 20min to the left and right of the 3 dot target. Subjects constantly viewed the 3 dot target and reported the first perceptible blur of the left dot as it moved toward the subject and the right dot as it moved away. Lag was measured by Nott retinoscopy in the same apparatus. 27 subjects between 18 and 33 years of age met the inclusion criteria and completed the study.
RESULTS: The average range of DOF was 0.51D±0.27 for the 2D demand and increased to 1.99D±0.46 for the 6D demand consistent with previous reports. The lag also varied with the demand, 0.34D± 0.29 (2D demand) and 1.04D± 0.66 (6D demand). Surprisingly, the lag frequently fell outside the DOF (59% outside DOF at 2D; 35% outside DOF at 6D).
CONCLUSIONS: These results suggest the link between blur perception and accommodative response is not always as expected since for some individuals the least perceptible blur does not provide a sufficient error signal to alter accommodation.
ADDITIONAL COMMENTS: NEI T35 EY07088
|Affiliation of Co-Authors||University of Houston, College of Optometry, University of Houston, College of Optometry, University of Houston, College of Optometry|