Steven R. Ali

Assessing visual performance with progressive addition lenses.

Purpose. As a result of lens design limitations, progressive addition lenses (PAL’s) present a limited field of view for tasks at intermediate distances, such as with computers. To assess whether this limitation results in diminished visual performance, PAL’s were compared with single-vision lenses in four different types of reading tasks in a computer workplace environment. Methods. Adult subjects performed four computer-based reading tasks using both single-vision lenses and PAL’s at an intermediate distance of 64 cm. Results. Single-vision lenses performed significantly better than PAL’s in one task, with a trend for better performance in another task. There was no difference in performance for the remaining two tasks. Conclusions. Visual performance tests that involved stimuli subtending the widest visual angles and demanded more fixational shifts were more sensitive in discerning performance differences between the lens designs. In general, PAL’s showed marginally diminished performance compared with single-vision lenses, presumably due to their restricted intermediate channel.

Rotational stability of toric soft contact lenses during natural viewing conditions.

Purpose. To compare objectively the rotational stability of two differently designed toric soft contact lenses over a range of natural viewing conditions using a novel infrared, video-based technique. Methods. Two contact lenses using different methods of stabilization were assessed: Accelerated Stabilization Design (ACUVUE ADVANCE for ASTIGMATISM) and Lo-Torque Design (B&L SofLens Toric). Four tasks involving saccades were performed: settling time with free viewing, reading, visual search, and execution of large versional tasks. Lens position (degrees of rotation) was continuously recorded with a head mounted, infrared, video-based system and a digital photo slit-lamp in 20 adult subjects. All measurements were obtained from the left eye under binocular viewing conditions with contact lenses on both eyes. Results. The ACUVUE lens was significantly more stable during the settling time and large saccadic versional tasks than the SofLens. For the two other tasks (reading, visual search), performance was similar. Conclusion. The ACUVUE design was superior in stability for two of the four conditions tested. This resulted in a more stable lens immediately after insertion as well as during some visual tasks involving either naturally occurring or programmed large versional eye movements. Both lens designs provided acceptable performance in terms of induced astigmatism produced by off-axis rotation.