Myofascial trigger point development from visual and postural stressors during computer work.

The mechanism of musculoskeletal pain underlying low level static exertions, such as those experienced during computer work, is poorly understood. It was hypothesized that static postural and visual stress experienced during computer work might contribute to trigger point development in the trapezius muscles, resulting in myofascial pain. A study was conducted to observe the development of myofascial trigger points while 16 female subjects used a computer under conditions of high and low postural and visual stress. Trigger point development was monitored via expert opinion, subject self-report, and electromyographic activity. Only the high visual stress conditions resulted in greater trigger point sensitivity as reported by subjects and the myofascial specialist. Cyclic trends in median frequency of the EMG signal were assessed for the trapezius muscle. When high visual stress was combined with low postural stress condition there were significantly fewer cycles (1.6 cycles) as compared to the condition of low visual and low postural stress (2.8 cycles), and the condition of high visual and high postural stress (3.5 cycles). These significant differences between conditions were found for the right trapezius but not for the left. The findings suggest that high visual stress may be involved in the development of the myofascial pain response.

Diurnal visual changes in radial keratotomy: implications for visual standards. Refractive Surgery Study Group.

BACKGROUND: Diurnal variations in vision have been reported in radial keratotomy (RK) patients. Applicants to certain professions may meet an uncorrected vision standard at the time of testing but fail to meet that standard at another time. METHODS: Ten firefighter applicants who had undergone RK and nine normal subjects attended for two morning visits, and two afternoon visits. At each visit subjective refraction, uncorrected visual acuity, best-corrected visual acuity, automated refraction, and keratometry were measured for each eye. Monocular contrast sensitivity was measured using the Pelli-Robson chart with and without a glare source (brightness acuity tester, BAT) and for both natural and dilated pupils. RESULTS: The RK group showed a significant myopic shift from morning to afternoon (mean = -0.41 +/- 0.33 D; t = 3.92, p = 0.004), which was well correlated (r = -0.86) with significant steepening of the corneal curvature (mean = +0.41 +/- 0.36 D; t = -3.65, p = 0.005). The controls showed no change in either refractive error (mean change = +0.06 +/- 0.42 D) or corneal curvature (mean change = +0.05 +/- 0.08 D). No significant difference in corrected visual acuity or contrast sensitivity was found between the RK and control groups for natural pupils. For dilated pupils, the RK patients showed significantly poorer log contrast sensitivity both with and without glare (RK mean = 1.49 +/- 0.11; control mean = 1.67 +/- 0.11; t = 3.21, p = 0.005). All RK subjects met the firefighter visual acuity standard on the initial visit, three subjects did not meet the standard at an afternoon examination. DISCUSSION: We propose that, if RK applicants are to be considered for employment, existing visual standards be amended to include visual acuity testing in both the early morning and late afternoon. Clinicians and agencies should also be aware that contrast sensitivity may be reduced at low light levels.

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.

Vision problems at video display terminals: a survey of optometrists.

One thousand three hundred seven optometrists responded (25.3 percent response rate) to a mail questionnaire concerning VDT patients in their practice. On the average, 14.25 percent of optometric patients present with symptoms primarily associated with use of the VDT, or almost 10 million examinations annually when projected to the U.S. population. A majority (55.3 percent) reported that their VDT patients have symptoms that are different than other near point workers, especially as related to glare, lighting, unique viewing conditions and spectacle requirements, and the greater frequency and severity of symptoms. They judged that they were unable to arrive at a confident diagnosis and treatment plan for 20.87 percent of VDT patients, which was significantly more than the 14.05 percent for non-VDT patients. Uncorrected refractive errors, accommodative disorders, irritated eyes, binocular vision disorders, and spectacle design problems were the most frequently cited diagnoses. On the average, 39.3 percent of their VDT patients receive a special VDT prescription or spectacle design that is different than they would require for other daily activities. They judged that 36.8 percent of the symptoms were related to visual environmental factors, primarily glare, lighting, screen resolution and work arrangement. The best way to resolve symptoms for VDT workers is to provide thorough vision examination and treatment in conjunction with diagnosis and treatment of visual environmental problems.

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.

Occupational and environmental disorders of the special senses.

Occupational hazards to vision, hearing, balance, olfaction, and taste typically constitute a small fraction of specialty medical practices in ophthalmology and otolaryngology. With the possible exception of noise-related hearing loss and VDT eye hazards, the scientific literature regarding these hazards tends to be scattered and variably accessible to occupational medicine practitioners. It is hoped that the current review will heighten the appreciation of these hazards among both generalists and specialists, and will encourage future documentation and reporting of this interesting group of disorders.

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.

Noninvasive assessment of the visual system and ophthalmic and visual optics: an introduction to the joint vision features.

This is an introduction to the joint feature on noninvasive assessment of the visual system and ophthalmic and visual optics.

Task and visual performance with concentric bifocal contact lenses.

We evaluated the effects of concentric simultaneous vision bifocal contact lenses on task performance, visual acuity, and stereopsis. Forty extensively screened presbyopes were fitted with CIBA Spectrum center-near bifocal contact lenses (BCL) and with distant contact lenses combined with reading spectacles (DCL) which served as the control. Thirty-two subjects completed the 8-week study. At dispensing and after 8 weeks of regular BCL wear, performance times with BCL were significantly greater than with DCL for all three near tasks. BCL generally resulted in more errors per trial. Visual acuities with BCL were reduced significantly by 0.8 to 1.4 acuity lines compared to DCL. Stereopsis was reduced significantly by 32 to 36 sec arc with BCL compared to DCL at both measurement sessions. It is likely that the decreased task performance with the simultaneous vision BCL is caused by the decreased visual acuity with these lenses. Nonetheless, 27 patients (58.7% of those selected to be fitted; 67.5% of those who were fitted) chose to wear the BCL on a regular basis at the study conclusion. Thus, even though BCL reduced task and visual performance, thoroughly screened and properly fitted presbyopic patients can become satisfied BCL wearers. However, the reduced task and visual performance with BCL should be considered when evaluating prospective BCL candidates.

Patient response to concentric bifocal contact lenses.

We evaluated the visual results and success rate with a center-near concentric simultaneous vision bifocal contact lens. Forty subjects (screened from 175 presbyopic applicants) entered the study and were fitted with the CIBA Spectrum bifocal lenses (BCL) and also with single vision distance contact lenses combined with reading glasses (DCL). Visual acuity and stereoacuity measurements were made at dispensing and after 8 weeks of regular bifocal contact lens wear. At both times, visual acuity measurements with BCL were significantly reduced by 1-1.5 lines compared to DCL. Stereoacuity was reduced by 32-36" with BCL compared to DCL. Thirty-two patients completed the study and 27 chose to continue wearing BCL after completion of the study. None of the subjects had adverse corneal findings or problems of discomfort. The primary reason for BCL discontinuation was blurred vision. The data was retrospectively analyzed to identify risk factors for discontinuance--none were significant.

Use of the Humphrey Lens Analyzer for off-axis measurements of spectacle lenses.

Automated focimeters can be used to make quick, precise measurements of off-axis power and prismatic effects corresponding to an eye rotating behind a spectacle lens. An automated focimeter, the Humphrey Lens Analyzer, was assessed in this regard. The Humphrey Lens Analyzer can be used to give a valid measure of off-axis power of lenses with low power, but not of lenses with moderate to higher power (greater than 3 D). For 3 D spherical lenses discrepancies of the order of 0.1 D occur at 30 degrees rotation, and 6 D spheres give discrepancies of 0.5 D at the same rotation. Small discrepancies were found for measurements of prism. The Humphrey Lens Analyzer was also used in a mode where the lens being tested is rotated about the center of curvature of its back surface. This is the mode often used to assess aberrations and prism of progressive-addition lenses. In this mode, the instrument provides reasonable accuracy in estimating off-axis power corresponding to eye rotation for lenses with low power, but not for lenses with moderate to higher power (greater than 3 D). However, it provides accurate values of the variation in off-axis surface power for low powered lenses with aspheric front surfaces. There were considerable systematic errors associated with the measurement of prism. A simple raytracing method was developed to predict the results of measurements with the Humphrey Lens Analyzer. Predictions of off-axis power were good when lenses were rotated about a position corresponding to the center-of-rotation of an eye, but were poorer when lenses were rotated about the center of curvature of their back surfaces. Predictions of primatic efforts were good in both situations. A method by which the Humphrey Lens Analyzer should provide an accurate measurement of off-axis powers corresponding to eye rotation behind a spectacle lens is described, but has not been tested.

The Video Display Terminal Eye Clinic: clinical report.

The Video Display Terminal Eye Clinic was designed to relieve the symptoms of video display terminal users by diagnosing and treating visual problems and by analyzing the patients' work station environment through an in-office simulation and making suggestions for improvements. The Clinic was open to the public and patients were therefore self-selected. The symptoms, diagnoses, and treatments were compiled retrospectively and reported for 153 patients. Vision problems were diagnosed in most patients. The most frequent diagnoses included: presbyopia, improper spectacle design for presbyopia, accomodative deficiencies, esophoria, exophoria, and hyperopia. The results suggest that proper visual care and work station arrangement can improve comfort.

Task performance with base-in and base-out prism.

The effects of base-in (BI) and base-out (BO) prism upon performance of four occupational-like tasks were measured on a group of 10 subjects who had normal binocular vision. Performance on tasks which required depth perception was significantly poorer when subjects wore prism glasses with 8 and 12 delta BI and BO, whereas 4 delta BI and BO did not significantly affect performance. The performance decrements with prism (3.0 to 6.7%) were considerably less than those induced by denial of binocularity (20 to 30%) as measured in a previous study. Thus, vergence-inducing prism does impair task performance but not as much as does the denial of binocularity. The reading and counting tasks did not require critical depth judgement and were much less affected by the prism than the needle-threading and pointers-and-straws tasks.

Monovision contact lens wear and occupational task performance.

The effects of monovision (MV) contact lens wear on the performance of occupational-type nearpoint tasks was evaluated on 18 presbyopic subjects (ages 44 to 67 years) by comparing MV performance (MV condition) to that with distance contact lenses with reading glasses (BV condition). Each subject had correctable distance visual acuity of 6/6 (20/20) in each eye, at least 60 sec arc of near stereopsis, good ocular health, and no previous MV experience. Time performance and error performance for 3 nearpoint occupational tasks (pointers and straws, card filing, and letter editing) were measured with the MV correction and BV correction. Measurements were taken at dispensing and at 2 weeks and 8 weeks after dispensing. Subjects were instructed to wear the MV soft spherical contact lenses at least 8 h per day. We measured BV time performance to be better than MV time performance by 2.8 to 5.7% and also measured an increased number of errors with MV.

Effect of filters upon object color naming.

Color constancy refers to the phenomenon that the perceived colors of objects are largely unaltered by changes in the illuminant or by viewing through colored filters. Deviations from perfect constancy, induced by filters similar to ophthalmic tints, were investigated in this study. Munsell color chips were forced-choice categorized into R, Y, G, or B. This accurately located the boundaries between these colors on the chip color circle. Testing was performed through 23 different adaptive conditions and chromaticity shifts created by filters. The technique simulates real world situations in which the chromaticity of the objects and the adaptation of the observer both change. Generally, color constancy held quite well. The boundaries between the four colors shifted for some filters, indicating some deviation from perfect constancy. Red filters resulted in more color chips appearing red, blue and green filters resulted in more chips appearing blue, and filters along the Planckian locus resulted in more chips appearing green.

Optics of progressive addition lenses.

The optical characteristics of the major progressive addition lenses were measured using an automated lensometer with a specially designed lens holder to simulate eye rotation. Measurements were made every 3 degrees (about 1.5 mm) and graphs of isospherical equivalent lines and isocylinder lines were developed. Generally the near zone of these lenses is narrower and lower than in bifocal or trifocal lenses. Distinct differences exist between the various progressive lenses. The width of the near zone, rate of power progression, amount of unwanted cylinder (level with the distance center), and clarity of the distance zone are compared for the various lenses. The optical measurements demonstrate an apparent trade-off between the size of the cylinder-free area of the lens and the amount of the cylinder.

Vertical yoked prism--patient acceptance and postural adjustment.

Vertical yoked prism is sometimes incorporated into multifocal lenses to obtain a thinner lens, or prescribed for oculomotor deficiencies, or occurs if the vertical placement of spectacle lenses before the eyes is inappropriate. Patient acceptance of and postural and perceptual adaptation to such prism were studied. Twenty-three subjects wore spectacles with no vertical prism and also with bilateral vertical yoked prism. The subject population could not significantly differentiate between 2 delta base down and 0 delta. There was a nearly unanimous rejection of 4 delta base down. Postural changes were significant during 4 delta wear but not during 2 delta wear. The results suggest that 2 delta may be accepted by most patients, but 4 delta will not.