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Biomedical subjects

R A Applegate

Publications and source records attributed to R A Applegate.

At least 37 records · Page 2Linked to original sources
PubMed1992

Set shot shooting performance and visual acuity in basketball.

Common sense suggests that decreasing visual acuity will have a negative effect on basketball shooting performance. To test the hypothesis that basketball shooting performance monotonically decreases with decreasing acuity, 19 subjects attempted 25 set shots from a fixed location at each of 5 different acuity levels: 6/6 or better and vision blurred (by optical defocus) to visual acuities of 6/12, 6/24, 6/48, and 6/75. Our results revealed a small but statistically nonsignificant decrease in shooting performance between the 6/6+ and 6/12 conditions. For visual acuities between 6/12 and 6/75, the number of baskets made remained constant. We conclude that decreases in visual acuity over the range of 6/6+ to 6/75 resulting from defocus do not significantly reduce set shot shooting performance.

Adolescent↗
PubMed1992

Psychophysical measurement of the size and shape of the human foveal avascular zone.

We have examined two psychophysical procedures for assessing the size and shape of the human foveal avascular zone (FAZ). Both procedures used a Maxwellian view system with a rotating beam to create a high contrast entoptic view of the retinal vasculature. Most subjects readily report a clear avascular zone surrounding their fixation point. The size of this FAZ was measured by (a) reducing the circular Maxwellian view field stop until it appeared to coincide with the edge of the FAZ, and (b) by tracing the boundary of the FAZ with a point source. Consistent with earlier angiographic and anatomical studies, the first method (N = 34 eyes) showed a mean FAZ diameter of 0.736 mm (area 0.42 mm2). FAZ diameter ranged from 0.46 to 1.13 mm (area 0.166-1.00 mm2) and the FAZ from the right and left eyes of each individual subject were very similar (r2 = 0.863). The tracing technique (n = 24 eyes) showed that FAZ's were generally not spherical but well fit by ellipses with, on average, a major axis 17% longer than the minor axis. The maximum diameters of the FAZ tracings were very similar and significantly correlated with the circle diameters matched to the FAZ in experiment 1.

Adult↗
PubMed1991

Acuities through annular and central pupils after radial keratotomy.

The corneal radius of curvature after radial keratotomy (RK) increases centrally in the surgery-free area while remaining relatively unchanged paracentrally and peripherally in the surgical areas. These corneal topography changes suggest that the imaging properties of the cornea should vary with the area of the cornea allowed to participate in image formation. To test this hypothesis visual acuities were measured both through a central and an annular pupil for normals and RK patients as a function of time after surgery. Annular acuities were decreased significantly after RK and remained decreased over time. Best corrected central acuity increased as a function of time after surgery, becoming significantly better than presurgery acuities but not as good as normals with similar low refractive corrections. Clinical implications include: (1) variations in visual performance (e.g., acuity, contrast sensitivity, glare) and optical quality measures (e.g., refraction, higher-order aberrations) as a function of pupil size; (2) use of a large a surgery-free area as possible; (3) careful centering of the surgery-free area on the natural pupil; (4) new contact lens designs for correcting RK patients' residual refractive error; and (5) counseling patients in general, and patients with naturally large pupils in particular, concerning possible variation in visual function with pupil size. In summary, this study indicates that postsurgery RK paracentral/peripheral corneal optics experience a loss in optical quality as compared to either normal eyes with a low refractive correction or the same eye before surgery.

Adult↗
PubMed1990

Entoptic visualization of the retinal vasculature near fixation.

The authors review (1) the range of techniques used to study the retinal vasculature near the fovea, (2) describe the need and rationale for noninvasive in vivo monitoring of the retinal vasculature, (3) present theoretic and practical considerations which show that entoptic visualization of the smallest capillaries near the fovea is optimized by a small short-wavelength source (1 mm or less) rotating at 3.5 hertz in a circular path (radius 2 mm) imaged in the plane of the eye's entrance pupil, and (4) discuss the feasibility of using these techniques as a research and clinical tool.

Fixation, Ocular↗
PubMed1990

Retinal fixation point location in the foveal avascular zone.

The site of normal fixation is often assumed to be centered in the foveal avascular zone (FAZ). This assumed anatomic relationship is used during photocoagulation therapy as an objective guide to avoid damaging critical retinal structures on or near fixation. With laser therapy being directed closer and closer to the center of the FAZ, the accuracy with which the center of the FAZ locates the retinal point of fixation becomes an important therapeutic issue. Using an optimized technique for visualizing the retinal vasculature entoptically, the authors determined the location of the retinal point of fixation with respect to the foveal area vasculature in 26 eyes of 14 healthy subjects. In 23 eyes (12 subjects), a traditional FAZ was observed, the other three eyes (two subjects) had capillaries near or crossing the center of fixation. Of the 23 eyes with a traditional FAZ, 20 had centers of fixation located eccentric to the center but in the FAZ, (average deviation from the center of the FAZ, 66.5 +/- 49.5 microns) with the direction of deviation from the FAZ center appearing random. Consequently, when following protocols that advocate photocoagulation treatment with spot centers closer to the FAZ center than 300 microns, the center of the FAZ is a poor locator of a subject's retinal point of fixation. When using the FAZ as a reference, the resulting uncertainty in the location of the subject's retinal point of fixation increases the probability of significant damage to the actual point of fixation by up to 20%.

Adolescent↗
PubMed1989

Disability glare and hydrogel lens wear--revisited.

Decreased tolerance to glare is a common complaint among hydrogel contact lens wearers. Recently this subjective complaint was measured and quantified in our laboratory in five subjects by determining increment thresholds as a function of background luminance and glare source location for both spectacles and hydrogel lens refractive corrections. Additional testing, using the same apparatus and similar protocols, has not entirely supported the original result. After testing a total of 15 subjects, data averaged across all subjects revealed no significant hydrogel contact lens-induced increases in disability glare; however, analysis of individual data revealed three classes of effects within the population tested. Subjects either demonstrated a significant glare effect induced by contact lens wear (6 of 15), no increase in disability glare (7 of 15), or a significant decrease in disability glare (2 of 15).

Adult↗
PubMed1987

Disability glare increased by hydrogel lens wear.

Decreased tolerance to glare is a common complaint in hydrogel contact lens wearers; yet, to our knowledge, the effect has never been quantified. By measuring increment thresholds as a function of background luminance and glare source location in two experimental conditions, while wearing a hydrogel contact lens correction and while wearing the spherical equivalent of their contact lens correction in a trial frame, we were able to quantify a significant contact lens-induced increase in glare-related visual disability. The effect is maximal at low background luminance levels, increases as the angle between the glare source and target decreases, and becomes lost in noise at high background luminance levels.

Adult↗
PubMed1987

Radial keratotomy increases the effects of disability glare: initial results.

Attempts to correct myopia by surgical intervention (radial keratotomy) are increasing, and disability glare is emerging as a common subjective postsurgical complaint. To date, efforts to quantify this complaint have failed. By measuring increment thresholds in the presence of a point-glare source, we have been able to measure large glare effects (up to six times normal) at low background luminance levels.

Humans↗
PubMed1986

Transient visual anomalies associated with drug treatment for spastic colon.

A case report revealing two previously unreported adverse side effects of meprobamate and tridihexethyl chloride (Milpath) drug therapy for a spastic colon is presented. The two previously unreported adverse effects are a diffuse loss of color discrimination and an increased time course to complete dark adaptation.

Colonic Diseases, Functional↗
PubMed1986

Total occlusion does not disrupt photoreceptor alignment.

Previous measurements of the photopic Stiles-Crawford function (SCF) in human observers prior to, during, and after (1) total occlusion, and (2) displacement of the eye's pupil, indicate by inference the presence of a phototropic mechanism which actively maintains photoreceptor alignment. In an attempt to replicate and expand the conclusions of these experiments, full SCFs were measured on three normal eyes and one abnormal eye prior to and after at least 6 days total occlusion. Counter to previous reports, total occlusion induced few if any alterations in the SCF rho value in both the normal and abnormal eyes.

Darkness↗
PubMed1985

Adverse consequences of altering the Farnsworth-Munsell 100-Hue test.

Modifications of the Farnsworth-Munsell 100-Hue test (e.g., selection of new fixed-reference caps from within the test) have been proposed, with little or no theoretical justification or experimental verification. Predictions based on theoretical considerations of the underlying nature of the test and verified by experimental measurements on subjects with known color defects demonstrate that (1) modification can destroy the very nature of the test; (2) modification can alter axis determination and therefore, potentially, the diagnosis; (3) the resulting test scores cannot be compared reliably to established norms; and (4) accurate predictions of test performance can be made from theoretical considerations.

Color Perception↗
PubMed1981

Induced movement of receptor alignment toward a new pupillary aperture.

Bonds and MacLeod (1978) reported on an individual whose receptors, as measured by the peak of the Stiles-Crawford function, were oriented in the direction of a traumatically displaced pupil. In an attempt to demonstrate that this orientational response is caused by an active alignment process and not simply a result of passive forces due to the traumatic ocular injury, we attempted to influence receptor alignment in the same eye by artificially creating a centered pupil. This was accomplished by placing on the subject's dilated eye a soft contact lens containing a centered 2mm artificial pupil. Receptor alignment (inferred from the entrance pupil location of the peak of the Stiles-Crawford function) significantly changed (0.8 mm) in the direction of the "new pupil" over a time course of 5 days. This alignment persisted for as long as the pupil was worn (1 month). With removal of the artificial pupil, the receptor alignment returned to its original eccentric orientation in 5 days. The results indicate that an active phototropic mechanism significantly influences receptor alignment toward the pupillary aperture.

Contact Lenses, Hydrophilic↗
PubMed1976

Contact lens surface damage related to cases and case removal techniques.

Surface damage incurred as a result of removing polymethyl methacrylate (PMMA) contact lenses form various contact lens carrying cases was monitored by photographic techniques. As compared to the controls, the experimental lenses showed consistent increases in surface damage, particularly if they were removed by a sliding (dragging) motion along the contours of the case.

Contact Lenses↗
PubMed1975

Changes in the contrast sensitivity function induced by contact lens wear.

Contrast sensitivity functions (i.e. minimum contrast required to resolve a sine wave grating as a function of spatial frequency) were determined for subjects when wearing normal spectacle corrections and when wearing either hard or soft contact lenses. Corections provides a more definitive evaluation of visual performance with contact lenses than do the conventional clinical procedures.

Adult↗
PubMedDate not supplied

Forward light scatter at one month after photorefractive keratectomy.

BACKGROUND: Although it is known that backward light scatter increases transiently following most excimer laser photorefractive keratectomies (PRKs), it is not clear that there is a significant increase in forward light scatter, which is of primary concern for the patient. The object of this study was to determine if there is a significant change of forward light scatter at 1 month after (PRK) with an ablation zone diameter of 6 mm. METHODS: Overlapping subsets of 24 normal myopic eyes were tested before (on the day of surgery) and 1 month after PRK, using three instruments: a Stray Light Meter (16 eyes); a Computerized Stray Light Meter (14 eyes); and a mesopic Increment Threshold-Glare Paradigm (six eyes). Differences between the two eyes before PRK were compared with the differences between the same eye before and after PRK, using repeated measured analysis of variance. In addition, increment threshold data obtained from 22 eyes after PRK were compared with those of 60 controls of the same age range and distribution by a t test. RESULTS: None of the statistical comparisons approached significance at the alpha = 0.05 level. Changes in light scatter as small as a factor of 1.95 (Stray Light Meter) and 1.55 (Increment Threshold-Glare Paradigm) could be detected as significant with a high power (0.8). Changes larger than a factor of 21 could be detected with a power of 0.8 for the Computerized Stray Light Meter. CONCLUSIONS: In these data, there is no support for the hypothesis that forward light scatter increases significantly 1 month after PRK with an ablation zone of 6 mm. Any increases in forward light scatter are unlikely to be greater than a factor of 1.5 to 2 under daytime or nighttime illumination conditions.

Adult↗
PubMedDate not supplied

Refractive surgery, optical aberrations, and visual performance.

Visual optics is taking on new clinical significance. Given that current refractive procedures can and do induce large amounts of higher order ocular aberration that often affects the patient's daily visual function and quality of life, we can no longer relegate the considerations of ocular aberrations to academic discussions. Instead, we need to move toward minimizing (not increasing) the eye's aberrations at the same time we are correcting the eye's spherical and cylindrical refractive error. These are exciting times in refractive surgery, which need to be tempered by the fact that after all the research, clinical, and marketing dust settles, the level to which we improve the quality of the retinal image will be guided by the trade-off between cost and the improvement in the quality of life that refractive surgery offers.

Cornea↗