Please use the archived list on the right to look at past peer-reviewed articles.
Barton,J. J. S., Rizzo,M., Nawrot,M., Simpson,T. Optical blur and the perception of global coherent motion in random dot cinematograms. Vision research 1996;36,19:3051-3059. [ Show Abstract ]
We evaluated the effect of +3.25 dioptres of optical blur on the discrimination of motion direction in random dot cinematograms. Dot displacement between frames varied from 2.1 to 63' of visual angle while the temporal interval was held constant. Optical blur worsened discrimination in three normal subjects at displacements below 16', but improved discrimination at displacements of 21' or more. In a second experiment, two subjects viewed equivalent velocity stimuli constructed with different combinations of temporal interval and spatial displacement. Results showed that the effect of blur was specific to displacement and not velocity. Furthermore, varying the dot density of the display showed that the effect of blur correlated with dot displacement and not the probability of dot mismatches. Since optical blur attenuates high spatial frequencies, this suggests that high spatial frequencies are important for motion perception when dot displacements are less than 16' to 21', but reduce motion perception at larger dot displacements. The use of random dot cinematograms in populations must take into account stimulus displacement and optical causes of reduced spatial acuity.
Barton,J. J. S., Simpson,T., Kiriakopoulos,E., Stewart,C., Crawley,A., Guthrie,B., Wood,M., Mikulis,D. Functional MRI of lateral occipitotemporal cortex during pursuit and motion perception. Annals of Neurology 1996;40,3:387-398. [ Show Abstract ]
We performed functional imaging with a conventional 1.5-T magnetic resonance scanner in 9 normal subjects. We used a gradient-echo technique to examine changes in signal between periods when subjects viewed a stationary black-and-white grating, a moving grating, and when they followed a moving spot. We located image pixels with significant differences between the viewing conditions. In 7 subjects, these occurred in the lateral occipitotemporal cortex, a region previously identified as a putative human homologue of the motion-sensitive middle temporal area (MT, or V5) of monkeys. Signal intensity was greater during pursuit of the moving dot than during viewing of the moving grating with the eyes still, despite the fact that the moving grating generated more retinal image motion. In contrast, signal intensity in striate cortex was least during pursuit of the moving dot. These findings suggest that the lateral occipitotemporal cortex has extraretinal signals during pursuit. Such signals may include attentional input, corollary eye movement information, or even a pursuit command. Extraretinal signals suggest that the lateral occipitotemporal cortex may contain a human homologue not only of MT but also of other components of the monkey V5 complex, such as the medial superior temporal area.
Fonn,D., Pritchard,N., Garnett,B., Davids,L. Palpebral aperture sizes of rigid and soft contact lens wearers compared with nonwearers. Optometry and Vision Science 1996;73,3:211-214. [ Show Abstract ]
Previous studies have shown that contact lens wear may affect palpebral aperture size (PAS). In this study, 74 wearers of rigid lenses were matched for sex and age with soft lens wearers and nonwearers. Partial face photographs were taken of all subjects, in the case of contact lens wearers, after lens removal. PAS was determined by measuring the resulting 35-mm transparencies on a Mitutoya profile projector. The mean PAS of the rigid lens wearers (9.76 ± 0.99 mm) was found to be significantly smaller than that of the soft lens wearers (10.24 ± 0.94 mm) and the nonwearers (10.10 ± 1.11 mm) (p = 0.0154, analysis of variance). There was no significant difference between the PAS of soft lens wearers and nonwearers. This study supports the hypothesis that rigid lens wear causes a decrease in PAS.
Pritchard,N., Fonn,D., Weed,K. Ocular and subjective responses to frequent replacement of daily wear soft contact lenses. CLAO Journal 1996;22,1:53-59. [ Show Abstract ]
Purpose: A significant number of soft contact lens wearers develop complications as a result of lens contamination. We conducted a single-blind 2 year clinical trial to determine if scheduled frequent replacement of lenses decreases complications. Methods: One hundred nineteen non-contact lens wearers were fit with soft contact lenses and randomly assigned to 1 or 3 month replacement schedules or a non-replacement (control) group. All subjects were fit with 0.04 mm thick HEMA (water content: 38%) lenses to be worn on a daily wear basis only. A single multipurpose solution was prescribed for cleaning and disinfection. Results: The 2-year results showed a significantly greater number of subjects in the non-replacement group exhibited microcysts, infiltrates, clinically significant corneal staining, and limbal and bulbar injection. As a result of lens deposition and damage, approximately twice the number of unscheduled lens replacements per subject were necessary in the non-replacement group compared with the 1 and 3 month replacement groups. Overall subject satisfaction with lens wear decreased in the non-replacement group and increased in the 1 and 3 month replacement groups over the 2-year period. Conclusions: Frequent replacement of soft lenses for daily wear as compared to non-replacement daily wear: 1) is less likely to cause contact lens induced complications; 2) reduces the number of unscheduled lens replacements; and 3) improves satisfaction with lens wear.
Sorbara,L., Fonn,D., Holden,B. A., Wong,R. Centrally fitted versus upper lid-attached rigid gas permeable lenses. Part I. Design parameters affecting vertical decentration. International Contact Lens Clinic 1996;23,3:99-104. [ Show Abstract ]
The purpose of this study was to develop rigid gas permeable lens designs that would facilitate upper lid attachment and central (interpalpebral) positions. A pilot study was conducted with trial lenses of varying back surface designs and axial edge lifts (AELs) with and without lenticulated front surface designs. From this study, the final upper lid attachment lens was designed to have high AELs (150–300 mm) and a minus carrier lenticulation. The centered lenses had an AEL of 110 mm, with thin edges. Forty-one neophyte subjects were fitted with these two designs to be worn contralaterally for an 8-month period during which the consistency of the lens position was examined. We were unable to achieve upper lid attachment on 6 subjects, and a further 10 were discontinued for other reasons. Of the remaining 25 subjects who completed the study, 80% had consistent upper lid attachment in the one eye and a centered lens in the other, over the eight visits. The balance of the subjects demonstrated correct lens positioning for at least 50% of the visits. The lens design factors that correlated with vertical decentration of the lenses were AEL (r = 0.614), edge thickness (r = 0.751), and front surface carrier radius (r = 0.654).