Biomedical subjects

Steven R Ali

Publications and source records attributed to Steven R Ali.

4 recordsLinked to original sources

PubMed2005

"Bothersome blur": a functional unit of blur perception.

Knowledge regarding the amount of blur perceived to be "bothersome" to an individual, namely that which is assumed to be annoying and to adversely affect task performance, remains limited. A Badal optical system was used to measure the blur detection, bothersome blur, and non-resolvable blur dioptric thresholds monocularly either to an isolated 20/50 or 20/200 Snellen E, or to three 20/50 lines of text. Subjects were comprised of 13 visually normal young adults and 3 absolute presbyopes. Cycloplegia was used to paralyze accommodation in the young adults. Within each target type for the young adults, the mean bothersome blur threshold was always significantly larger than that found for blur detection and significantly smaller than that found for non-resolvable blur. Across target types and blur criteria, the bothersome blur thresholds for the isolated 20/50 E (1.02 D) and the 20/50 text (1.34 D) were not significantly different, although in 12 of the 13 subjects the latter were larger (p<0.002, sign test). However, both were significantly smaller than for the isolated 20/200 E (1.80 D). In a subset of young adult subjects, bothersome blur was found to be repeatable over time. The results were similar in the absolute presbyopes. The bothersome blur threshold was primarily influenced by target detail and secondarily by target extent. These findings have important implications with respect to tolerances for optical lens design and refractive surgery outcomes, as well as provide insight into basic aspects of human blur perception.

Accommodation, Ocular↗

PubMed2003

Static aspects of eye and head movements during reading in a simulated computer-based environment with single-vision and progressive lenses.

PURPOSE: Reading with two different intermediate progressive lens designs was investigated regarding eye and head movement patterns and compared with movement patterns with a conventional single vision lens in a computer-based work environment. METHODS: Two-dimensional eye (horizontal, vertical) and three-dimensional head (horizontal, vertical, and torsional) movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of moderate contrast (40%) single- and double-page text formats at 60 cm with binocular viewing. In addition, global reading ability was rated subjectively for each lens. Subjects were 11 visually normal, presbyopic individuals aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses: a single-vision lens (SVL; 60 degrees horizontal [H] clear field-of-view [FOV]); a progressive addition lens (PAL) with a relatively wide intermediate zone (PAL-I; 7.85 mm, 18 degrees H clear FOV); and a PAL with a relatively narrow intermediate zone (PAL-II; 5.60 mm, 13 degrees H clear FOV). RESULTS: Many reading-related parameters, as well as eye- and head-movement parameters, were adversely affected by the PALs compared with the SVL. One reading-related parameter (i.e., number of regressions) differentiated between PALs. Subjective rating of global reading ability was highest with the SVL and lowest with the PAL-II. CONCLUSIONS: The optical design of a spectacle lens had significant impact on reading performance and on the combined eye-head movements initiated during reading. Both horizontal eye and head movements discriminated well between PALs and the SVL, but not between PALs, despite subjective preferences. This suggests that nonoculomotor factors contribute to patients' nonacceptance of PALs. Vertical eye and head movements and torsional head movements were not as discriminatory as were their horizontal counterparts.

Aged↗

PubMed2003

Dynamic interactions of eye and head movements when reading with single-vision and progressive lenses in a simulated computer-based environment.

PURPOSE: To assess dynamic interactions of eye and head movements during return-sweep saccades (RSS) when reading with single-vision (SVL) versus progressive-addition (PAL) lenses in a simulated computer-based business environment. METHODS: Horizontal eye and head movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of single-page (SP; 14 degrees horizontal [H]) and double-page (DP; 37 degrees H) formats at 60 cm with binocular viewing. Subjects included 11 individuals with normal presbyopic vision aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses with a different clear near field of view (FOV): a SVL (60 degrees H clear FOV), a PAL-I with a relatively wide intermediate zone (7.85 mm; 18 degrees H clear FOV), and a PAL-II with a relatively narrow intermediate zone (5.60 mm; 13 degrees H clear FOV). RESULTS: Eye movements were initiated before head movements in the SP condition, and the reverse was found in the DP condition, with all three lens types. Duration of eye movements increased as the zone of clear vision decreased in the SP condition, and they were longer with the PALs than with the SVL in the DP condition. Gaze stabilization occurred later with the PALs than with the SVL in both the SP and DP conditions. The duration of head movements was longer with the PAL-II than with the SVL in both the SP and DP conditions. Eye movement peak velocity was greater with the SVL than the PALs in the DP condition. CONCLUSIONS: Eye movement and head movement strategies and timing were contingent on viewing conditions. The longer eye movement duration and gaze-stabilization times suggested that additional eye movements were needed to locate the clear-vision zone and commence reading after the RSS. Head movements with PALs for the SP condition were similarly optically induced. These eye movement and head movement results may contribute to the reduced reading rate and related symptoms reported by some PAL wearers. The dynamic interactions of eye movements and head movements during reading with the PALs appear to be a sensitive indicator of the effect of lens optical design parameters on overall reading performance, because the movements can discriminate between SVL and PAL designs and at times even between PALs.

Aged↗

PubMed2002

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.

Adult↗