Biomedical subjects

James E Sheedy

Publications and source records attributed to James E Sheedy.

11 recordsLinked to original sources

PubMed2005

Visual effects of the luminance surrounding a computer display.

The luminance surrounding a computer display can potentially reduce visibility of the display (disability glare), result in sensations of discomfort (discomfort glare) and result in transient adaptation effects from fixating back and forth between the two luminance levels. The study objective was to measure the effects of surround luminance levels upon these functions in younger and older adults to determine recommended surround luminance levels. The younger age group comprised 20 subjects (mean age 27.9 years, range 23 - 39) and the older group 17 subjects (mean age 55.5 years, range 47 - 63). The central task was presented with luminance of 91 cd/M(2), tested surround luminance levels were 1.4, 2.4, 8.9, 25.5, 50, 91, 175, 317, and 600 cd/M(2). Disability glare was tested with low contrast (20%) visual acuity charts, transient adaptation was tested with a task that required regular fixation between the two luminance levels, discomfort was measured with a questionnaire after reading stories with different surround luminance levels, and preferred luminance was measured by method of adjustment. The surround luminance significantly affected transient adaptation (p < 0.0001), optimal performance occurred at 50 cd/M(2) and above for the young group and at 91 cd/M(2) and above for the older group. Neither low contrast acuity (disability glare) nor symptoms when reading were significantly affected by surround luminance. There was wide variation in preferred surround luminance; however, average preferred surround luminance was 86.9 cd/M(2) for the young group and 62.2 cd/M(2) for the older group, slightly below the central luminance of 91 cd/M(2). The effects of the surround luminance within the tested range are not large; however, the data show that the lowest surround luminance levels should be avoided and that surround luminance levels at or slightly below that of the central task are preferred.

Adaptation, Physiological↗

PubMed2005

The optics of occupational progressive lenses.

BACKGROUND: Occupational progressive lenses (OPLs) utilize progressive power optics and are designed primarily to meet near and intermediate viewing needs such as working at a computer workstation for presbyopic patients. OPLs are fabricated to have the prescribed near power in the lower part of the lens and the power in the upper portion of the lens is determined by the amount of power "degression" (decrease in plus power) relative to the near power. Independent measurements of the optical characteristics of these lenses have not been reported previously. METHODS: Manufacturers of 7 different OPL designs provided sample lenses for a patient with +2.50 D add that were measured with a Rotlex Class Plus lens analyzer (Rotlex Inc., Israel). Power measurements were normalized to the location specified by the manufacturer, and the vertical location of each lens was normalized to pupil center based on manufacturer fitting guidelines. RESULTS: Large optical differences exist among the OPL designs. The results show clear differences between the designs in terms of the add powers, their vertical location, and zone width. The size and location of the near, near-intermediate, far-intermediate, and far viewing zones were determined. CONCLUSIONS: The literature and clinical experience support that OPLs are successful at meeting the computer, general office, and other intermediate viewing distance needs of many patients. However, because of the large differences in the several OPL designs, patient success can likely be enhanced by selecting the design that best suits his or her viewing needs.

Computer Terminals↗

PubMed2005

Blink rate decreases with eyelid squint.

PURPOSE: We hypothesize that eyelid squint inhibits blink rate. This is part of a larger hypothesis that, because eyelid squint improves vision under conditions of optical defocus and/or glare, and reduced blink rate is assumed to contribute to dry eye symptoms, eyelid squint is part of the mechanism resulting in asthenopia. This study investigates the effect of voluntary eyelid squint on blink activity and on electromyography (EMG) measures from the orbicularis oculi. METHODS: Ten subjects (18 to 38 years of age) performed 3 1-minute trials each (Latin Square order) of voluntary target squint levels of 5%, 20%, 35%, and 50% with respect to previously demonstrated 0% (relaxed) and 100% (maximum) squint levels. EMG recordings using surface electrodes were obtained from the orbicularis muscle. Vertical dimension of the palpebral fissure and eye lid blinks were measured with an ISCAN eye tracker and video recorder. RESULTS: Each target squint level produced significant changes (p<0.0001) in ocular aperture size, EMG power, and EMG amplitude. For target voluntary squint levels of 5%, 20%, 35%, and 50%, the mean squint responses were 24%, 35%, 42%, and 53%, respectively. Blink rate was inversely related to both target squint level and squint response (p<0.0001), decreasing from 15 blinks per minute at 0% squint to 7.5 blinks per minute at 5% target voluntary squint and to 4 blinks per minute at 50% target voluntary squint. CONCLUSIONS: Voluntary eyelid squint significantly reduces blink rate by an average of 50% or more dependent on attempted level. Further study is required to determine if involuntary squint causes the same. All tested levels of voluntary squint resulted in an EMG signal from the orbicularis muscle that is measurably different from resting state. This indicates that EMG can be used as a reliable indicator of eyelid squint.

Adult↗

PubMed2005

Progressive powered lenses: the Minkwitz theorem.

PURPOSE: The Minkwitz theorem, which can be proven to apply to the immediate surface surrounding a line of umbilics, states that astigmatism perpendicular to the line changes twice as quickly as the rate of change of power along the line. Our objective is to test how the Minkwitz theorem applies to the design of progressive addition lenses (PALs). METHOD: Our primary investigation of the astigmatism/power rate relationship used Hoya Tact lenses because they have a relatively large central region with horizontal spherical equivalent power contours and vertical astigmatism power contours. Other PALs were used for subsequent analysis. Lenses were measured with a Rotlex Class Plus lens analyzer. RESULTS: Zone widths in the central region of the Tact lenses exceeded those predicted by the Minkwitz theorem. Above and below this region, zone widths were narrower than predicted. When averaged along the entire corridor, zone widths approximated the Minkwitz theorem. For other PALs, the measured zone widths exceed Minkwitz theorem in the top (distance) and middle (intermediate) corridor but fell short in the lower (near) corridor. Likewise, on average along the entire corridor, they approximate the Minkwitz theorem. CONCLUSIONS: Although the Minkwitz theorem must apply exactly to the immediate locale of an umbilic, deviations from Minkwitz can occur within 2 mm of the corridor. Several factors enable enough local deviation from the Minkwitz theorem to "steer" the astigmatism and affect its magnitude in the peripheral portions of a lens. Although the Minkwitz relationship may be altered in some regions of the corridor, there is a global component to the Minkwitz prediction that applies to PALs. On a global level, the gains and losses of astigmatism along the corridor with respect to the Minkwitz prediction have strong tendency to cancel one another. In the end, it appears the unwanted astigmatism associated with a given power change along a given distance can be redistributed but probably not reduced.

Astigmatism↗

PubMed2005

Text legibility and the letter superiority effect.

Effects of font design and electronic display parameters upon text legibility were determined using a threshold size method. Participants' visual acuity (inverse of the minimum detection size, representing the threshold legibility for each condition) was measured using upper- and lowercase letters and lowercase words in combinations of 6 fonts, 3 font-smoothing modes, 4 font sizes, 10 pixel heights, and 4 stroke widths. Individual lowercase letters were 10% to 20% more legible than lowercase words (i.e., lowercase words must be 10%-20% larger to have the same threshold legibility). This letter superiority effect suggests that individual letters play a large role and word shape plays a smaller role, if any, in word identification at threshold. Pixel height, font, stroke width, and font smoothing had significant main effects on threshold legibility. Optimal legibility was attained at 9 pixels (10 points). Verdana and Arial were the most legible fonts; Times New Roman and Franklin were least legible. Subpixel rendering (ClearType) improved threshold legibility for some fonts and, in combination with Verdana, was the most legible condition. Increased stroke width (bold) improved threshold legibility but only at the thinnest width tested. Potential applications of this research include optimization of font design for legibility and readability.

Adolescent↗

PubMed2004

Progressive addition lenses--matching the specific lens to patient needs.

BACKGROUND: The objective of this study was to use state-of-the-art methods to measure the optical characteristics of commonly available progressive addition lenses (PALs) and to develop derivatives of the optical measurements that can be used as guidelines in selection of lenses based on patients' visual needs. METHODS: The optics of 28 PALs currently on the market were measured with a Rotlex Class Plus lens analyzer. PALs were specified with plano distance power and a near add of +2.00 D. Data were normalized to plano at the location specified by each manufacturer and acquired from each data file in 1-mm vertical steps with respect to the fitting cross. RESULTS: The variance across lenses was greater than 2:1 for most measurements. Ratings were calculated based on equal weighting of zone width and area for distance, intermediate, and near zones, and also for magnitude of unwanted astigmatism. CONCLUSIONS: The results demonstrate wide ranges of optical characteristics across the PALs tested in this study. Ratings of the distance, intermediate, and near zones, as well as rating of unwanted astigmatism can be used in selection of appropriate lenses to match patient visual needs.

Eyeglasses↗

PubMed2004

Correlation analysis of the optics of progressive addition lenses.

PURPOSE: To investigate the relations between selected key optical parameters and the sizes of the clear viewing areas of progressive addition lenses (PALs). METHODS: The optics of 28 PALs (plano with +2.00 D add) currently on the market were measured with a Rotlex Class Plus lens analyzer. Horizontal cross sections were analyzed in 1 mm vertical steps with respect to the fitting cross. Distance, intermediate, and near viewing zone widths and areas were calculated from the measurements. The maximum amount of unwanted astigmatism, minimum zone width (0.50 DC limit), and maximum power rate in the corridor were also recorded for each lens. Correlation coefficients were determined for all relations. RESULTS: Each of the three viewing zone areas had a significant negative relation with the other (r of -0.4 to -0.8), indicating design tradeoff. Maximum power rate was significantly related to minimum zone width (r = -0.695), which was significantly related to maximum astigmatism (r = -0.616), but there was not a significant relation between maximum power rate and maximum astigmatism. Higher power rates and narrower minimum zones were significantly related to smaller intermediate and larger near zones (r = 0.4 to 0.9). Maximum astigmatism was related to distance zone width (r = 0.42) and to intermediate zone size (r = -0.4 to -0.56), but not significantly related to near viewing zone. Power rate and astigmatism each vary relatively uniformly across each lens. CONCLUSIONS: The fundamental relation appears to be between power rate and zone width, each of which is highly related to sizes of the intermediate and near viewing zones. The maximum amount of astigmatism is related to zone width, but not to maximum power rate. The amount of astigmatism is unrelated to the size of the near zone. The pattern of correlations between the optical and viewing zone parameters help identify the underlying optical relations of PALs.

Eyeglasses↗

PubMed2004

Ultraviolet eye radiation: the problem and solutions.

Ultraviolet radiation (UVR) can cause damage to the eyes. Some of the damage is acute, with immediate signs and symptoms, while some of the damage is the result of cumulative or long-term UVR exposure. Because the most common source of UVR is the sun, individuals who are exposed to sunny environments should be advised to protect themselves properly. Individuals should be counseled about proper eye protection from UVR in sunlight. It is important to know when eye protection is indicated. Protection involves wearing a wide-brimmed hat or cap and well-designed sunglasses. The advisable sunglass features include the following: large eye size with side protection, less than 1% UV-B transmittance, less than 1% UV-A transmittance, gray or near-neutral colored lenses, good optical quality, and visible transmittance selected for visual comfort. Some clear spectacles or contact lenses also provide good levels of UV protection. When selecting sunglasses, it is always helpful to consult your eye care specialist.

Eye Diseases↗

PubMed2003

Is all asthenopia the same?

PURPOSE: Any of several conditions can cause asthenopia. The purpose of this study was to determine whether the particular sensations or their location vary dependent on the symptom-inducing condition. METHODS: Twenty subjects with good vision performed eight reading tasks in random order during different conditions. Each condition used different stimuli to induce asthenopia. The eight conditions were mixed astigmatism, close viewing distance, upward gaze, dry eyes, lens flipper, small font, glare, and flickering light. Subjects were asked to read until attaining a level of discomfort self-defined as "barely tolerable." After each task, subjects rated the magnitude of several symptom descriptors (burning, ache, strain, irritation, tearing, blurred vision, double vision, dryness, and headache) and their location. RESULTS: Analysis of variance with repeated measures was used to determine that all of the individual symptom sensation measures (except blur) were significantly related (p values ranged from 0.003 to <0.0001) to the inducing condition. Principal factor analysis with orthogonal varimax rotation was used to test symptom by condition relationships and determined two latent factors, designated external and internal symptom factors (ESF and ISF), that related symptoms to inducing condition. The ESF pattern comprises burning, irritation, tearing, and dryness located in the front and bottom of the eye. ESF is caused by holding the eyelid open, glare, up gaze, small font, and flickering. ESF seems highly related to dry-eye symptoms. The ISF pattern comprises ache, strain, and headache located behind the eyes. ISF is caused by the close viewing distance, lens flipper, and mixed astigmatism conditions and is likely related to accommodative and vergence stress. CONCLUSIONS: Symptom descriptors and locations were able to distinguish discomfort on the basis of causative condition. Results support two different symptom constellations and, hence, at least two different afferent pathways for symptoms of asthenopia.

Accommodation, Ocular↗

PubMed2003

What are the visual benefits of eyelid squinting?

PURPOSE: We propose that eyelid squint can reduce the impact of several conditions known to cause eyestrain such as uncorrected refractive error, accommodative dysfunction, presbyopia, and glare. Clinicians commonly accept that squint improves visual acuity (VA) in the presence of refractive error, and even though the benefit of eyelid squint in bright light seems self-evident, data are not available to support either benefit. The purpose of this study was to measure the effect of eyelid squint on VA in the presence of refractive blur and on visual field sensitivity. METHODS: Nineteen subjects with optimal refractive correction were tested, with and without squinting, as follows: (1) distance VA with induced refractive errors of +0.50, +1.00, +2.00, +3.00, +1.00 -1.00 x 90, and +1.00 -1.00 x 180; (2) near VA with induced refractive errors of -1.00 x 90 and -1.00 x 180; and (3) central and peripheral threshold visual fields with a Humphrey Field Analyzer. Differences in visual acuity between squinting and nonsquinting were tested for significance with repeated-measures analysis of variance, and differences in visual fields were tested using mixed model analysis of variance with repeated measures. RESULTS: Eyelid squint significantly improved (p < 00.016) distance VA measurements for 1.00 to 3.00 D of induced myopia. The squint-induced VA improvement increased from 0.06 logarithm of the minimum angle of resolution for 1.00 D to 0.24 logarithm of the minimum angle of resolution for 3.00 D of myopia. Eyelid squint also significantly reduced visual field sensitivity below the horizontal meridian by an average of 1.4 dB, by 1.6 dB on the horizontal meridian, and with increasing reductions in the vertical field up to 11.6 dB for measurements 40 degrees above fixation. This pattern of decreased superior field sensitivity would decrease visual discomfort from overhead glare. CONCLUSIONS: The results provide empirical support that eyelid squint improves visual acuity for subjects with refractive error and reduces glare in the superior visual field.

Adult↗

PubMed2002

The efficacy of computer glasses in reduction of computer worker symptoms.

BACKGROUND: Computer workers with presbyopia are at greater risk for the development of symptoms with a conventional prescription vs. a computer prescription because general-wear multi-focal corrections often do not provide adequate correction for the viewing distances and angles needed at the computer workstation. "Computer glasses," as defined by the American Optometric Association, are specifically designed for the computer workplace and have a different lens design or prescription than general-wear glasses. The purpose of this study is to evaluate the effectiveness of computer glasses in reduction of symptoms of presbyopic computer users. METHODS: Subjects were 26 symptomatic presbyopic computer users who had had an eye examination within the past year and had 20/20 vision at distance and near with habitual glasses. Two interventions in planned alternating order were tested for 3 weeks each on all subjects. One intervention was computer glasses. The comparison intervention was an ergonomic self-assessment tool (ESAT) with their habitual Rx. Symptoms were assessed before and after each intervention. A post-comparative questionnaire asked subjects to reflect on the relative efficacy and ease of use of the two interventions. RESULTS: The computer glasses were significantly more effective at reducing the frequency and severity (p < 0.008) of the symptoms than the ESAT, and 24 of 26 subjects judged the computer glasses to bemore effective. Subjects attributed 80.7% of symptom reduction to the computer glasses and 19.3% to the ESAT. Although the ESAT was judged effective, it was not as effective as the computer glasses. CONCLUSION: Computer glasses have been shown to be effective in reduction of vision-related symptoms of computer users.

Computers↗