The portrayal of optometry in the media.
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Humans↗
Biomedical subjects
M G Harris
Publications and source records attributed to M G Harris.
Induced motion may account for the illusory transformation of optic flow fields found by Duffy and Wurtz.
Duffy and Wurtz [(1993) Vision Research, 33, 1481-1490] found an illusory shift in the position of the focus of expansion (FOE) of random dot patterns when planar motion was superimposed on expanding radial motion. Subjects indicated that this illusory shift was in the direction of the planar motion. This is the opposite direction to a true shift in the FOE that is perceived when the planar motion is vector summed with the expanding motion. We account for this illusion by suggesting that planar motion induces opposite motion on the expanding dots which after vector summation produces the illusory shift in the FOE. We use a matching technique with a method of adjustment to measure induced motion and perceived FOE in moving random dot patterns and present the results in support of our assertion.
Humans↗
Speed gradients and the perception of surface slant: analysis is two-dimensional not one-dimensional.
Motion parallax provides cues to the three-dimensional layout of a viewed scene and, in particular, to surface tilt and slant. For example, as a textured surface, inclined around a horizontal axis, translates horizontally relative to an observer's view point, then, in the absence of head and eye movements, the observer's retinal flow will contain a one-dimensional (1D) vertical speed gradient. The direction of this gradient indicates the direction of surface tilt, and its magnitude and sign can be used in calculating the magnitude and sign of the surface slant. Alternatively, the same retinal flow contains a 1D translating component, plus a two-dimensional (2D) component of rotation (curl), and a 2D component of deformation (def). On this view, the direction of surface tilt is related to the orientation of def and the magnitude and sign of the surface slant is related to the magnitude and sign of def. We used computer generated random dot patterns as stimuli to determine whether the human visual system employs a 1D analysis (i.e. 1D speed gradients) or a 2D analysis (i.e. deformation) of surface slant from motion parallax. Using a matching technique we found compelling impressions of slant when we vector summed a translation field with (i) vertical shear, horizontal shear or deformation (made from vertical and horizontal shear), but not rotation; and (ii) vertical compression, horizontal compression or deformation (made from vertical and horizontal compression), but much less so for expansion. In both cases, the first three conditions contain def, but the fourth does not, and the last three conditions contain 1D speed gradients orthogonal to the perceived axis of inclination, but the first one does not. Therefore, the results from the first and fourth conditions distinguish between the two processing strategies. They support the idea that surface slant is coded by combining both horizontal and vertical speed gradients in a way similar to the 2D differential invariant def and oppose the view that surface slant is encoded by a 1D analysis of motion in a direction orthogonal to the perceived axis of inclination. In a further experiment, we found essentially no effect of reducing the field size from 18 to 9 deg.
Cues↗
Soft lens movement: effects of humidity and hypertonic saline on lens settling.
Hydrogel contact lenses require a settling period before lens fit stabilizes, but the process underlying the initial reduction in lens mobility is poorly understood. Explanations for this phenomenon include base curve steeping with dehydration, expulsion of postlens tear fluid, and osmotic flow of hypotonic tears into the cornea. We conducted two randomized, single-masked interocular comparisons for ten subjects wearing HEMA lenses for 1 h. We investigated potential mechanisms of dehydration-dependent lens tightening, by limiting dehydration in one eye using a high humidity environment (experiment 1), and of a hypotonic lacrimation-dependent decrease in lens movement, by presoaking lenses in isotonic (0.9%) or hypertonic (1.5%) saline (experiment 2). Lens mobility profiles were not significantly affected by modification of environment; lenses in both normal and high humidity environments displayed a significant reduction in lens movement during the first 15 min of wear (ANOVA, p = 0.0001), and no change in lens mobility thereafter. Lens mobility profiles were identical for lenses presoaked in isotonic and hypertonic saline, with initial lens movement being significantly greater than for subsequent measurements (ANOVA, p < 0.05). These studies find no evidence to support dehydration-dependent steepening of base curve, or osmotic-dependent binding from hypotonic lacrimation as mechanisms for the initial postinsertion decrease in lens movement.
Adult↗
Fluoxetine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in older patients with depressive illness.
The selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor fluoxetine is an effective antidepressant in elderly patients. Its efficacy is similar to that of other frequently used antidepressants, such as the tricyclic antidepressants. However, compared with the tricyclic antidepressants, fluoxetine has a more favourable tolerability profile and is less toxic in overdose. It is associated with fewer anticholinergic, cardiovascular and CNS adverse events, but greater numbers of gastrointestinal adverse events than have been reported for the tricyclic antidepressants. This is important in elderly patients who are more at risk of developing central anticholinergic and cardiovascular effects than are younger patients. Therefore, while its position relative to other selective serotonin reuptake inhibitors requires investigation, fluoxetine represents a major advance over tricyclic antidepressant agents in the treatment of elderly patients with depression, predominantly because of its favourable tolerability profile.
Aged↗
Challenges facing optometric education.
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Education, Continuing↗
Ultraviolet transmittance of contact lenses.
Chronic and acute exposure to ultraviolet (UV) radiation has been shown to have deleterious effects on all layers of the human eye. As a consequence, appropriate protective measures have been advocated with respect to exposure to this form of radiation. Among suggested actions are spending less time in the sun and wearing protective visual aids such as those containing UV-absorbing materials when exposed to sunlight. To investigate the protective ability of currently available contact lens materials we measured the transmittance characteristics of 11 different types of soft and rigid contact lenses in the UV and visible range from 280 to 500 nm with a Zeiss model DM4 Dual Beam Spectrophotometer. Our findings indicate that lenses not treated with UV absorbers transmitted most of the UV radiation. Lenses containing UV absorbers provided excellent UV protection and transmitted significantly less UV radiation than the untreated lenses (Student's t-test with Bonferoni's correction, N = 10, p < 0.001). Based on our findings, we recommend that contact lenses with UV absorbers be considered as a viable option for providing UV protection, especially for aphakic patients, patients taking photosensitizing pharmaceutical agents, and those patients who spend a great deal of time outdoors.
Absorption↗
Human sensitivity to temporal proximity: the role of spatial and temporal speed gradients.
Estimates of temporal proximity (sometimes called time-to-collision) from random-dot flow patterns are shown to be based upon retinal speed, rather than upon changes in dot density. Neither the spatial nor the temporal gradient of motion is essential to the task, but estimates can be made from either alone. Performance is unaffected by the addition of rotational motion, suggesting that observers are capable of extracting the radial component of motion, which contains all the relevant information, from complex stimuli.
Acceleration↗
Blood pressure measurement by eye care practitioners.
We surveyed a random sample of 250 optometrists (OD) and 250 ophthalmologists (MD) in November 1991 to determine if they were involved in blood pressure measurement. A 50.4 percent and 34.8 percent response rate was obtained from ODs and MDs, respectively. Of those responding, 85 percent of the optometrists and 87 percent of the ophthalmologists reported that they did routinely question their patients about blood pressure, while 65.9 percent of the optometrists and 94.2 percent of the ophthalmologists reported owning blood pressure measurement equipment. Of those owning blood-pressure measuring equipment, approximately 20 percent of both professions reported measuring blood pressure on patients with a defined set of historical or observed risk factors. More optometrists should own blood pressure measurement equipment and measure blood pressure on a routine basis. The detection, referral, and co-management of hypertension by optometrists is important in providing primary health care.
Blood Pressure↗
Contact lens fitting should not be delegated to technicians.
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Contact Lenses↗
Does the presbyopic visual system adapt to contact lenses?
We studied whether task performance improves during the initial wearing period of selected presbyopic contact lens corrections. In three previous studies significant decreases in performance on three selected tasks were measured before and after initial wearing periods to monovision contact lenses (N = 18, 8 weeks of wear), concentric bifocal lenses (N = 32, 8 weeks), and diffractive and monovision lenses (N = 20, 3 weeks). In each study, the control condition was distance contact lenses with reading spectacles. The decreases in performance speed ranged from 2 to 15% compared to control. In this study, we retrospectively analyze the data to determine whether the task performance decreases relative to control were significantly different after the initial wearing period than at the time of dispensing--i.e., did measures of task performance show an adaptation to the presbyopic contact lens correction? Performance adaptation on each task and for each study was analyzed statistically using the Wilcoxon matched pair signed rank test of each subject's mean performance differences (test vs. control condition) at dispensing compared to the performance at the end of the wearing period. There was no improvement in task performance with monovision or diffractive bifocal lenses. However, we found significant improvements in task performance with concentric bifocal lenses (p < 0.05). Measures of visual acuity and stereoacuity did not improve with these lenses during the studied wearing period. Thus, these basic visual skills did not adapt. The ability of patients to learn how to use reduced visual acuity to perform complex tasks is a possible explanation for the improved task performance with concentric bifocal lenses compared to control.
Adaptation, Ocular↗
Effects of ultraviolet radiation on contact lens parameters.
Ultraviolet (UV) radiation has been proposed as an alternative method for contact lens disinfection. In order for UV radiation to be considered a viable contact lens disinfection method, its effects on lens polymers and parameters must be minimal. To evaluate this, soft contact lenses from each of the four FDA categories, soft lenses with handling tints, and rigid gas permeable (RGP) lenses were exposed to UV radiation in a controlled laboratory setting and their parameters measured. After 20 h of UV exposure, we found statistically significant changes in at least one parameter for each lens type evaluated. Most of these changes were small and within the error of measurement and, therefore, were not considered clinically significant. However, the group 2 soft lenses showed an increase in all four measured parameters--power, center thickness, diameter, and water content. These changes may have an impact on lens fitting characteristics and performance. Other than these changes for group 2 soft lenses, 20 h of UV exposure appeared to have little clinical effect on the contact lenses evaluated. This suggests that UV radiation may prove to be a feasible alternative method of disinfection for most types of contact lenses.
Contact Lenses, Hydrophilic↗
Ultraviolet disinfection of contact lenses.
To evaluate the efficacy of ultraviolet (UV) radiation as a method of disinfecting contact lenses and their storage solutions, we contaminated soft lenses (Bausch & Lomb Optima 38), rigid gas permeable (RGP) lenses (Oxyflow F-30), and their storage solutions with three common bacteria. Escherichia coli (E.c.), Staphylococcus epidermis (S.e.), and Serratia marcescens (S.m.). The storage solutions used were saline solution and RGP conditioning solution. We determined the exposure times to 253.7-nm wavelength UV radiation necessary to disinfect the contact lenses and solutions. The decimal reduction values (D values) found for UV radiation were 10 to 200 hundred times shorter than reported for currently available disinfection systems. For E.c., sterilization was attained after 100 s of exposure. For S.e. and S.m., sterilization occurred after 300 s of exposure. Different contact lens solutions transmit UV radiation to various degrees, with saline solution passing more than 90% of the UV radiation. Thus, our results indicate that UV radiation is an effective and rapid method of disinfecting contact lenses and their storage solutions.
Colony Count, Microbial↗
Microwave irradiation and soft contact lens parameters.
We evaluated the effect of repeated microwave irradiation on soft contact lens parameters to determine if microwave disinfection affects soft lens polymers or parameters. Ten factory-sealed lenses from each of the four FDA categories were placed in Ciba AOsept cases which were filled with 13 ml of sterile unpreserved saline. The cases were placed in a 10-cm diameter circle on the rotating plate of a standard 2450 MHz 650 W microwave oven and exposed to repeated 5-min cycles of microwave irradiation. The lens parameters, including back vertex power, back optic zone radius, diameter, thickness and water content, were measured over a period of 200 cycles to simulate over 6 months of daily disinfection. The postirradiation measurements were compared to baseline measurements taken before microwave exposure. We found statistically significant changes in many lens parameters, but all were small and few were clinically significant. These findings indicate that microwave disinfection does not have a clinically significant effect on the parameters of most unworn soft contact lenses. Further studies are needed to determine the long-term effects of microwave disinfection on worn soft contact lenses.
Contact Lenses, Hydrophilic↗
Improving health service management education: the manager speaks.
This paper uses health service manager judgements to discuss educational approaches and environments suitable to the development of required competencies and reports barriers to and opportunities for competency development. Practising managers were found to recognise and value the educational contributions made by academic programs, health service organisations and professional associations to the development of professional competence. Academic programs are seen as the appropriate vehicle for developing conceptual, analytical, problem solving and communication competencies that require considerable maturation time. Health service organisations are seen to have a key role in promoting professional competence through maintaining a culture conductive to encouraging managers to undertake further education, supported by appropriate system strategies. Professional associations are regarded as appropriate sponsors for promoting knowledge and skill update in relation to current issues in management through short courses, conferences and timely educational meetings. Wherever possible, collaboration between professional and educational organisations was seen to be desirable.
Adult↗
Human sensitivity to expanding and rotating motion: effects of complementary masking and directional structure.
A comparison of sensitivity to expanding, rotating, translating and random motion suggests the existence of specialised mechanism for the detection of expansion and rotation. Complementary masking shows that the detection of expansion is unaffected by the presence of rotation, and vice versa. These results are interpreted in terms of a Relative Motion System, which combines the outputs of localised motion detectors in a variety of ways, and which functions to analyse complex image motion into simpler, more useful, components.
Female↗
Task and visual performance with contact lenses and spectacles.
Previous studies found task and vision performance differences between presbyopic contact lens corrections and distant contact lenses combined with reading spectacles. The present study was designed to compare task and vision performance with single vision contact lenses and spectacles. Eighteen soft (SCL) and seventeen rigid gas permeable (RGP) successful contact lens wearers were examined and fitted with CR-39 spectacles (SPEX) which corrected their distance vision. Their occupational task performance and visual acuity (high contrast, low contrast, low contrast with glare) were measured while they wore their contact lenses and spectacles. The tasks included putting pointers in straws, filing cards in a box, counting letters on a photograph of a VDT screen, and a distance/near fixation task. Visual acuity scores were lower with SCL than with SPEX. Low contrast visual acuity with glare was reduced by 1.36 letters on a 5-letter row (p less than 0.05) for SCL compared to SPEX. No statistically significant differences in performance times were measured between contact lenses and spectacles. None of the error performance differences were statistically significant; however, more errors were made on each occupational task with soft contact lenses compared to spectacles. The findings suggest nearly equivalent task and visual performance with properly prescribed RGP contact lenses and spectacles, and minimal performance decrements with SCL compared to spectacles.
Adult↗
Vision and task performance with monovision and diffractive bifocal contact lenses.
We measured vision and task performance on 26 presbyopes, ages 46 to 65 years, fitted with diffractive bifocal contact lenses (BFCL) and monovision contact lenses (MVCL). Distance contact lenses combined with reading spectacles (DCL) served as the control condition. Twenty subjects completed the 6-week study. All subjects wore BFCL and MVCL daily for a period of 3 weeks each. Performance times for three near tasks were 6 to 8% longer with BFCL compared with DCL and 2 to 6% longer for MVCL compared with DCL. There were significant reductions in distance visual acuity with BFCL (0.4 to 1.5 Snellen lines) and MVCL (0.5 to 0.8 Snellen lines) compared to DCL. At the conclusion of the study, given a choice between BFCL and MVCL, 2 of the 20 subjects chose to continue wearing BFCL, whereas 18 of the 20 subjects chose MVCL. Our results show greater visual compromise and decreased task performance with BFCL and MVCL compared to DCL and greater patient preference for MVCL.
Aged↗