Changes In Visual Performance Research Articles

Changes in visual performance and appearance before manual reach movements

Changes in visual performance and appearance before manual reach movements

Recovery of visual performance in rosy rockfish ( Sebastes rosaceus) following exophthalmia resulting from barotrauma

Rapid ascent during fishing capture can cause exophthalmia (‘pop eye’) in physoclistic fishes, resulting in stretching of the optic nerves and extraocular muscles, but it is not known whether exophthalmia affects vision temporarily or permanently. We used the optokinetic reflex test to assess changes in visual performance of rosy rockfish ( Sebastes rosaceus) that had experienced exophthalmia. Vision was functional 4 days after recompression and was improved after 1 month of recovery evidenced by individuals being able to track both smaller and faster-moving gratings. Our results suggest that, after recompression, rosy rockfish recover from exophthalmia fairly rapidly and perhaps fast enough to minimize significant adverse impacts on survival. This measured recovery from exophthalmia, in addition to evidence of high short-term, post-release survivorship, shows that recompression of unwanted rosy rockfish may be a viable management technique, and may be appropriate for other rockfish species, some of which are at low population densities due to high fishing pressure.

Prognostic Indicators and Outcome Measures for Surgical Removal of Symptomatic Nonadvanced Cataract

To report changes in perceived visual functioning after surgery for symptomatic cataract with preoperative corrected distance visual acuity [CDVA] of 0.4 logMAR or better (Snellen equivalent, 20/50) and to investigate the relationship between any observed changes and preoperative physical characteristics and psychophysical consequences of the lens opacity and any changes in psychophysical findings after the procedure. Eighty-five patients with cataract completed a validated questionnaire concerning functional vision satisfaction and a series of visual performance assessments before and 2 months after cataract surgery. The lens optical density and Lens Opacities Classification System III score of the cataract were recorded. Correlations between changes in the Rasch-analyzed questionnaire score and changes in visual performance after cataract surgery, as well as preoperative psychophysical measures, lens optical density, and Lens Opacities Classification System III score, were determined. The mean (SD) questionnaire score improved from 2.15 (0.36) to 1.54 (0.41) (P < .001). The preoperative questionnaire score (r = -0.44), preoperative mesopic glare disability [GD] (at 1.5 cycles per degree [cpd] [r = 0.34] and 3.0 cpd [r = 0.27]), and preoperative photopic GD (at 1.5 cpd [r = 0.24] and 3.0 cpd [r = 0.30]) showed statistically significant correlations with perceived improvements in visual functioning after surgery (P < .05). Changes in perceived visual functioning correlated significantly with changes in mesopic GD (at 1.5 cpd [r = -0.43] and 3.0 cpd [r = -0.28]; P < .05) and photopic GD (at 1.5 cpd [r = -0.24] and 3.0 cpd [r = -0.39]; P < .05). Neither preoperative CDVA nor change in CDVA after surgery correlated significantly with perceived improvement in visual functioning after the procedure (P > .05 for both). Psychophysical tests alternative to CDVA better represent improvements in self-reported visual functioning following removal of symptomatic nonadvanced cataract.

Corneal aberrations and objective visual quality after hyperopic laser in situ keratomileusis using the Esiris excimer laser

To evaluate the changes in visual performance and ocular optical quality after hyperopic laser in situ keratomileusis (LASIK) using the Esiris excimer laser (Schwind eye-tech-solutions). Vissum-Instituto Oftalmológico de Alicante, Alicante, Spain. Excimer laser surgery was performed with the Esiris laser in 51 eyes of 29 patients with hyperopia or hyperopic astigmatism. The follow-up was 6 months. Changes in visual acuity, refraction, and corneal and ocular wavefront aberrations (6.0 mm pupil) were recorded and analyzed. The mean preoperative sphere was +4.45 diopters (D)+/-1.08 (SD) (range +2.50 to +7.25 D) and the mean preoperative cylinder, -0.55+/-0.36 D (range 0.00 to 1.00 D). Ten eyes (19.61%) had a LASIK enhancement during the follow-up for the correction of the residual refractive error and were excluded from the refractive analysis. Of the 41 remaining eyes, 95.12% had the same or improved distance best spectacle-corrected visual acuity (BSCVA) 6 months after surgery; 90.25% had no change or a gain of lines of near BSCVA. Moreover, 80.50% of eyes were within +/-0.50 D of emmetropia. Regarding corneal aberrations, statistically significant changes were observed in higher-order aberrations (HOAs), coma-like aberrations, and the primary spherical aberration coefficient Z(4,0), which changed from positive to negative values (all P<.01). Regarding total ocular aberrations, statistically significant changes were observed in total and higher-order root-mean-square values (P<.01). Hyperopic LASIK using the Esiris excimer laser for the correction of 2nd-order aberrations was safe and effective. Ocular and corneal HOAs increased significantly postoperatively.

Attention makes moving objects be perceived to move faster

Although it is well established that attention affects visual performance in many ways, by using a novel paradigm [Carrasco, M., Ling, S., & Read. S. (2004). Attention alters appearance. Nature Neuroscience, 7, 308–313.] it has recently been shown that attention can alter the perception of different properties of stationary stimuli (e.g., contrast, spatial frequency, gap size). However, it is not clear whether attention can also change the phenomenological appearance of moving stimuli, as to date psychophysical and neuro-imaging studies have specifically shown that attention affects the adaptability of the visual motion system. Here, in five experiments we demonstrated that attention effectively alters the perceived speed of moving stimuli, so that attended stimuli were judged as moving faster than less attended stimuli. However, our results suggest that this change in visual performance was not accompanied by a corresponding change in the phenomenological appearance of the speed of the moving stimulus.

Efficacy of Measuring Visual Performance of LASIK Patients under Photopic and Mesopic Conditions

The aim of the study was to compare the visual performance of LASIK eyes measured using high-contrast logMAR letter charts under bright (photopic) and dim (mesopic) conditions. A total of 46 subjects (35 +/- 8 years of age) undergoing LASIK procedures were recruited for the study. The best spectacle-corrected visual acuity (BSCVA) of each subject was measured using the high-contrast ETDRS logMAR chart under photopic and mesopic conditions at 3 visits: preoperative (Pre), 1 month postoperative (Post1) and 3 months postoperative (Post3). The differences in logMAR scores for the right eyes only were analysed for the Pre-Post1 (n = 46), Pre-Post3 (n = 18) and Post1-Post3 (n = 16) comparisons. The logMAR scores of subjects were worse at the 1-month postoperative visit than preoperatively, and improvement in visual performance was seen at the 3-month postoperative visit. These changes in visual performance became more evident under mesopic conditions. The means and standard errors of the differences in logMAR scores for the Pre-Post3 (0.097 +/- 0.020) were slightly larger than those of the Pre-Post1 (-0.067 +/- 0.019) and Post1-Post3 (0.031 +/- 0.012) comparisons. Under mesopic conditions, the visual performance of the subjects was statistically significant for the 3 comparisons, but not under photopic conditions. High-contrast logMAR chart performed under mesopic conditions has the potential to replace visual acuity measured under photopic conditions in providing more reliable representation of postoperative visual outcomes of LASIK eyes. Eye doctors should consider performing this vision test routinely to gauge the success of LASIK surgery.

Guest Editorial: Shedding new light on the twilight zone

Guest Editorial: Shedding new light on the twilight zone

The Role of Retinal Adaptation in Night Driving

Driving is essentially a visuomotor task, and there is now compelling evidence that the disproportionate number of road accidents under night driving conditions is linked to changes in visual performance resulting from reduced lighting. The objective of this article is to establish the extent to which vision is either rod-or cone-dominated under night driving conditions. Visual thresholds are measured under lighting conditions that simulate urban lighting. Dark adaptation curves are obtained under three ambient lighting conditions ranging from low (0.1 cd/m) to high (5 cd/m) mesopic levels of retinal adaptation using circular discs of different sizes (1 degree, 2 degrees, 3 degrees, and 5 degrees) presented at retinal eccentricities of 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 40 degrees. The dark adaptation curves exhibit the classic inflection point between rod and cone activity for the lower levels of ambient illumination but a simple monophasic function for the high mesopic levels (>0.5 lux). Adaptation rates are four times faster for the higher compared with the lower illumination level and twice as fast for central compared with peripheral presentation. The data suggest that vision is mediated by cone pathways at 5 lux and by rod pathways at 0.5/0.1 lux. This shift does not profoundly affect sensitivity, but because rod pathways are known to be slower than cone pathways, it will certainly affect observers' ability to respond to rapidly changing viewing conditions such as are encountered when driving at night.

LASIK and the contrast sensitivity function

We read with interest the work of Quesnel et al.1 They describe the clinical effects of laser in situ keratomileusis (LASIK) on the cornea and visual performance by the contrast sensitivity function (CSF). We agree with their comment that CSF measurement is necessary to assess visual function. For several years, our research group has evaluated the visual performance of refractive surgery patients by the CSF assessment.2–8 Quesnel et al. report that previous studies of CSF measurement were done under photopic conditions only. This is not true because our group has studied the effect of phototherapeutic keratectomy,3 LASIK,4,6,7 and other refractive surgeries8 on CSF under mesopic conditions. (Our study was cited in their references.) Quesnel et al. suggest that the reduction in CSF after LASIK cannot be attributed to optical defocus because they measured CSF with and without the best optical correction, yielding to similar results. They showed a postoperative spherical equivalent ranging from +0.75 to −0.75 diopter at 1 month (no data available for longer times). In our opinion, it is impossible to discount the negative effect of optical defocus on CSF measurement with these values. Lower levels of defocus than those reported by the authors significantly modify the CSF. Perhaps, in addition to defocus, microstriae such as they suggest would affect their results and a combination of defocus and mircrostriae plays a role in CSF reduction. More information about microstriae in their patients should be noted in the paper. Another point to discuss is that the authors failed to mention the pupil diameter of the patients under photopic and mesopic conditions, which affect the CSF, and the luminance of the room where CSF was measured (not lux values, which refer to illuminance, but cd/m2, nits, or apostilb units, which refer to luminance). Thus, no comparison with previous studies, especially those performed under mesopic conditions,4 could be done. Finally, we believe that CSF measurement is an excellent technique to report changes in visual performance in patients having laser refractive surgery, but caution will need to be taken in CSF measurement and the conclusions derived from this. Robert Montés-Micó OD, MPhil, PhD Jorge L. Alió MD, PhD Alicante, Spain

Visual performance in soft contact lens wear. Is there a compromise?

Purpose: A six‐month study was performed comparing a group of contact lens wearers against a group of age and refraction matched non‐contact lens wearers.Methods: Visual performance was measured by log MAR visual acuity (VA) and Pelli‐Robson contrast sensitivity (CS). Contact lens wearers were all established wearers of at least six months. Patients were refitted with Hydron Omniflex lenses. The care regimen was Alcon Opti‐free. Visual performance was measured every eight weeks with lenses in situ and any necessary over‐refraction, lenses were removed and visual performance was re‐measured with a full spectable refraction. The order of testing was randomised. In addition, the non‐lens wearers were also assessed every eight weeks.Results: Results suggest that for VA there is no significant change in visual performance with time in the contact lens wearers (F2.40 = 2.031,P &gt; 0.1) or the non‐lens wearers (F2.18 = 0.863, P &gt; 0.1). In addition, there is no significant difference in VA when comparing spectacle VA in the contact lens group against contact lens VA (F1.20 = 0.79, P &gt; 0.1). There is also no significant difference between VA in the non‐lens wearing group and either spectacle VA (F1.29 = 0.877, P &gt; 0.1) or CL VA in the lens wearing group (F1.29 = 1.646, P &gt; 0.1). When CS is measured there is again no significant change with time for lens wearers (F2.40 = 1.771, P &gt; 0.1) or non‐lens wearers (F2.18 = 0.053, P &gt; 0.1). There is, however, a significant drop in visual performance when comparing spectacle CS in the contact lens group against contact lens CS (F1.20 = 18.835, P = 0.0003) and non‐wearers against contact lens CS (F1.29 = 7.719, P = 0.009). There is no significant difference between CS in non‐lens wearers and spectacle CS in lens wearers (F1.29 = 0.982,P &gt; 0.1).Conclusion: These results suggest that even though visual performance measured by VA or CS in contact lens wearers does not deteriorate with lens age. CS is significantly worse when wearing lenses. It is also significantly worse than a non‐lens wearing population. As refractive error was accounted for in the protocol this is not the reason for the significant difference. Other causes of the significant reduction in performance may be lens movement, lens surface drying or lens deposition.Acknowledgements: We thank Hydron UK Ltd and Alcon for help in the form of contact lenses and solutions. Financial support was received from the Visual Research Trust.

Relative roles of resolution and spatial interference in foveal and peripheral vision

SummaryThe rate of change of visual performance with increasing eccentricity of fixation is known to be task dependent. In order to examine eccentricity‐related changes in visual performance when a combination of two different factors influence thresholds, visual acuity in the presence of flanking elements was investigated across the visual field. Interference zones increased in extent with eccentricity at a much faster rate than did resolution thresholds. E2 values, quantifying the eccentricity‐related magnification required, were 1–2° for resolution and 0.1–0.2° for spatial interference. E2 values for resolution in the presence of flanks depended on the proximity of the flanks and their ‘weighting’ in the task. From the results, the magnitude and extent of spatial interference across the visual field can be described quantitatively. Further, the results serve as an example of how observed variations in peripheral threshold gradients might be achieved as a combination of underlying factors with different E2 values.

Relative roles of resolution and spatial interference in foveal and peripheral vision

The rate of change of visual performance with increasing eccentricity of fixation is known to be task dependent. In order to examine eccentricity-related changes in visual performance when a combination of two different factors influence thresholds, visual acuity in the presence of flanking elements was investigated across the visual field. Interference zones increased in extent with eccentricity at a much faster rate than did resolution thresholds. E2 values, quantifying the eccentricity-related magnification required, were 1–2 ° for resolution and 0.1–0.2 ° for spatial interference. E2 values for resolution in the presence of flanks depended on the proximity of the flanks and their ‘weighting’ in the task. From the results, the magnitude and extent of spatial interference across the visual field can be described quantitatively. Further, the results serve as an example of how observed variations in peripheral threshold gradients might be achieved as a combination of underlying factors with different E2 values.

Visual Acuity Modeling Using Optical Raytracing of Schematic Eyes

We developed a methodology to predict changes in visual performance that result from changes in the optical properties of the eye. Exact raytracing of schematic eyes was used to calculate the point spread function and the modulation transfer function of the visual system. The Stiles-Crawford effect, photopic response, diffraction, and the retinal contrast sensitivity are included in the model. Visual acuity was predicted by examining the modulation of the resultant retinal image of a bar target and by determining when the modulation falls below a threshold value. Visual acuity was predicted for refractive errors ranging from 0 to 5 diopters and for pupil diameters ranging from 0.5 to 8 mm. Visual acuity predictions were compared to clinically found Snellen visual acuities and were found to be highly correlated (r2 = .909). This modeling technique shows promise as a means of evaluating clinical and surgical procedures before undertaking clinical trails.

Changes in ocular and visual variables during the menstrual cycle.

For most women the menstrual cycle is an integral part of a major portion of their lives. There is widespread agreement about the hormonal changes that occur during the menstrual cycle, but studies of physical and psychological changes have been more controversial. The influence of the menstrual cycle on various ocular and visual variables has been investigated. These include the potential protective role of female sex hormones in some ocular conditions, reports of reduced tolerance to contact lens wear, and changes in visual performance during the cycle. This paper critically reviews the literature on visual and ocular changes across the normal human menstrual cycle. Stereotypical views of an impairment of performance premenstrually and during menstruation are challenged. The shortcomings of, and difficulties associated with, much of the research on this topic are highlighted.

VDU work, contrast adaptation, and visual fatigue

Abstract Prolonged VDU work leads to a number of detrimental changes in visual performance and to frequent complaints about asthenopia, musculoskeletal, and other symptoms. The relationship between changes in contrast adaptation at five spatial frequencies and workrelated symptoms were studied in an experimental approach with two groups, one working 2 h (n=13) and the other 4 h (n = 17). Both groups showed a significant reduction in visual acuity and contrast sensitivity, but there were no significant differences between working two or four hours. The relationship between contrast adaptation and symptoms showed a mixed pattern. For the 2 h group there was significant positive correlation between symptoms and all spatial frequencies. For the 4 h group there were mixed correlations between symptoms and contrast adaptation. The results offer only partial support to Lunn and Bank's hypotheses on contrast adaptation, accommodation control and visual fatigue symptoms. Contrast adaptation saturates after 1-2 h and induces a short term effect on visual fatigue. For longer work periods posture-ergonomic and oculomotor factors will penetrate and dilute the contrast sensitivity effect.

Work, Aging, and Vision: Report of a Conference

The number of middle-aged workers is rising. The number of Americans 65 years of age and older will double to 50 million in the next 25 years. With these demographic changes in the US labor force,<i>Work, Aging, and Vision: Report of a Conference</i>is a timely and relevant publication. The aging of the human eye and the resulting changes in visual performance will, for some individuals, have an effect on job performance. A project of the National Academy of Science's Research Council and Committee on Vision,<i>Work, Aging, and Vision: Report of a Conference</i>reviews what is known about changing visual functions related to work performance and recommends steps to take to address changing visual needs. Brief and to the point, this report is based on the conference papers and discussions of 28 specialists drawn from the fields of gerontology, economics, sociology, statistics, psychology, political science, optometry, opthalmology, engineering,

Progressive Cone Dystrophy

Psychophysical, reflectometric, and electrophysiologic studies were done on four members of a dominant pedigree with progressive cone dystrophy. The two youngest individuals were asymptomatic at the initial examination, and none of the subjects complained of problems associated with night vision. Nevertheless, absent or grossly reduced cone-mediated electroretinographic (ERG) responses showed the widespread loss of cone function, and moderate elevations (<1 log unit) in absolute threshold together with reductions in rhodopsin levels in the mid-peripheral retina provided evidence of impairment of the rod system. The progressive nature of the disease was apparent from the case histories and the changes in visual performance that occurred on re-test after a 5-year interval. Moreover, the results of increment threshold measurements at several retinal loci suggested that peripheral cones may be affected earlier and more severely than those in the central retina.

Practical implications of a new visual performance model

Recommendations of illuminance are imprecise for specifying visual perfomance in lighted environments. A more exact method of determining visual performance in alphanumeric reading tasks has now been proposed. Predictions of visual performance over the range of lighting levels and task contrasts commonly experienced in commercial environments are possible with the model. Predictions of age-related changes in visual performance are also possible. Examples are provided. The model is based on the philosophy of psychophysics of lighting first described and implemented experimentally by Weston fifty years ago, but it and the study on which it is based go further. It is important that practitioners understand this philosophy and that future studies also adhere to its principles.

The design and use of a new near-vision chart.

This paper describes the design of a new near-vision chart that uses unrelated words arranged in a logarithmic progression of size and that has standardized the test task by controlling typeface, spacings, and number of words per row, and making each group of words of approximately equal difficulty. These charts offer special advantages for systematic assessment of reading acuity and visual efficiency for reading. The logarithmic progression of print size on these charts can be used to facilitate prediction of the magnitude of changes in visual performance resulting from changes in optical parameters, and the magnitude of changes in optical parameters required to achieve desired levels of visual performance. Simple methods for converting from point size scaling to M units or Snellen equivalents are also described.