Ian L. Bailey

New visual acuity charts for clinical research.

Three new visual acuity charts facilitate quantitative use of visual acuity test results. The charts have high-contrast lettering on washable white polystyrene. Each line has five Sloan letters; the lines are of equal difficulty and there is a geometric progression in letter size from line to line. This provides a similar task for each line on the chart with the letter size being the only variable. Charts with different letter sequences are used for testing right and left eyes.

Vision-threatening Complications of Surgery for Full-thickness Macular Holes

OBJECTIVEnTo study complications of vitrectomy surgery for full-thickness macular holes.nnnDESIGNnA multicentered, randomized, controlled clinical trial.nnnPARTICIPANTSnCommunity and university-based ophthalmology clinics.nnnINTERVENTIONnStandardized macular hole surgery versus observation.nnnMAIN OUTCOME MEASURESnAssessment of anatomic and visual outcomes and determination of postoperative complications at 12 months after randomization.nnnRESULTSnPosterior segment complications were noted in 39 eyes (41%). The incidence of retinal pigment epithelium (RPE) alteration and retinal detachment (RD) were 33% and 11%, respectively. One RD due to a giant retinal tear resulted in a visual acuity of light perception. Other complications included a reopening of the macular hole in 2 eyes (2%), cystoid macular edema in 1 eye (1%), a choroidal neovascular membrane in 1 eye (1%) and endophthalmitis in 1 eye (1%). Eyes with complications had significantly worse visual acuity outcomes as determined by the Early Treatment Diabetic Retinopathy Study, Word Reading, and Potential Acuity Meter charts (P < 0.01 for all comparisons). Eyes with macular holes greater than 475 microns were more than twice as likely to have complications than eyes with holes less than 475 microns (odds ratio [OR] = 2.2, P = 0.07). Before surgery, the stage of the hole was related to postoperative RPE changes (P < 0.0001) and the occurrence of postoperative RD (P = 0.0002). Intraoperative trauma was related to the occurrence of these complications (P < 0.0001 for RPE changes, P = 0.02 for RDs). Epiretinal membrane removal was related to RPE changes (P = 0.02) but not RDs.nnnCONCLUSIONSnThe RPE alterations and RDs are common after macular hole surgery and result in significantly reduced postoperative visual acuity. The RPE changes may be related to surgical trauma or light toxicity. Further efforts to reduce complications associated with macular hole surgery are indicated.

Prospective randomized trial of vitrectomy or observation for stage 2 macular holes

Purpose To determine the risks and benefits of vitrectomy surgery in eyes with stage 2 macular holes. Methods A multicentered, controlled, randomized clinical trial was performed with participation of 16 community and university-based ophthalmology clinics. Thirty-six eyes with stage 2 macular holes and 12 months of follow-up were studied. Pars plana vitrectomy with separation of the posterior hyaloid membrane and intraocular injection of perfluoropropane (C3F8) was followed by postoperative face-down positioning for two weeks. This protocol was compared with observation alone. Outcome variables included anatomic closure of the macular hole, macular hole size, and four standardized measures of vision. Results At 12 months, 15 (71%) of 21 eyes randomly assigned to observation progressed to stages 3 or 4, compared with three (20%) of 15 eyes randomly assigned to surgery (P Conclusion Compared with observation alone, surgical intervention in stage 2 macular holes resulted in a significantly lower incidence of hole enlargement and appeared to be associated with better outcome in some measures of visual acuity.

Visual acuity testing. From the laboratory to the clinic.

The need for precision in visual acuity assessment for low vision research led to the design of the Bailey-Lovie letter chart. This paper describes the decisions behind the design principles used and how the logarithmic progression of sizes led to the development of the logMAR designation of visual acuity and the improved sensitivity gained from letter-by-letter scoring. While the principles have since been adopted by most major clinical research studies and for use in most low vision clinics, use of charts of this design and application of letter-by-letter scoring are also important for the accurate assessment of visual acuity in any clinical setting. We discuss the test protocols that should be applied to visual acuity testing and the use of other tests for assessing profound low vision when the limits of visual acuity measurement by letter charts are reached.

The Berkeley Rudimentary Vision Test.

Purpose. Very poor visual acuity often cannot be measured with letter charts even at close viewing distances. The Berkeley Rudimentary Vision Test (BRVT) was developed as a simple test to extend the range of visual acuity measurement beyond the limits of letter charts by systematically simplifying the visual task and using close viewing distances to achieve large angular sizes. The test has three pairs of hinged cards, 25 cm square. One card-pair has four Single Tumbling E (STE) optotypes at sizes 100 M, 63 M, 40 M, and 25 M. Another card-pair has four Grating Acuity (GA) targets at sizes 200 M, 125 M, 80 M, and 50 M. The third card-pair has a test of White Field Projection (WFP) and a test of Black White Discrimination (BWD). As a demonstration of feasibility, a population of subjects with severe visual impairment was tested with the BRVT. Methods. Adults with severe visual impairments from a wide variety of causes were recruited from three different rehabilitation programs. Vision measurements were made on 54 eyes from 37 subjects; test administration times were measured. Results. For this population, letter chart visual acuity could be measured on 24 eyes. Measurements of visual acuity for STE targets were made for 18 eyes and with GA targets, for two eyes. Five eyes had WFP, and one had BWD. Four had light perception only. The median testing time with the BRVT was 2.5 min. Discussion. The BRVT extends the range of visual acuity up to logMAR = 2.60 (20/8000) for STEs, to logMAR = 2.90 (20/16,000) for gratings and includes the WFP and BWD tests. Conclusions. The BRVT is a simple and efficient test of spatial vision that, with 13 increments, extends the range of measurement from the limits of the letter chart up to light perception.

Evaluating pterygium severity: A survey of corneal specialists

Purpose. Accurate and reliable evaluation techniques are essential for clinical and epidemiologic studies. This survey of corneal specialists was designed to lay a foundation for the further development of methods for evaluating and staging pterygium. Methods. In a self-administered, mailed questionnaire, 213 corneal specialists rated the importance of nine symptoms, nine signs, and nine clinical tests for the severity of primary pterygium. Severity was defined as the present need for surgical intervention. Results. The most important factors for determining primary pterygium severity were the extent of encroachment onto the cornea, decreased visual acuity, restricted ocular motility, and increased rate of growth. Many patient symptoms were rated as moderately to highly important. The questionnaire was shown to have good response reliability by test–retest comparisons. Cronbachs &agr; was 0.89, which indicates very good internal consistency reliability. Conclusion. The survey identifies the priorities of experts in determining the severity of pterygium. More precise and clearly defined evaluation methods will enhance future clinical and epidemiologic studies of pterygium. The ranked list of pterygium signs, symptoms, and tests can serve as a guide for developing pterygium evaluation methods in the future. There is a need for a method that accurately and precisely quantifies the distance of pterygium encroachment onto the cornea and the pterygium progression rate. Furthermore, there is a need for an assessment of patient symptoms.

Artificial pupils and Maxwellian view.

When control of the pupil size is required, the simplest method is to use a physical artificial pupil or aperture that is placed in the spectacle plane. In some clinical applications (e.g., the potential acuity meter) an optical artificial pupil is imaged in the plane of the natural pupil by a Maxwellian view optical system. We compared visual performance with physical and Maxwellian artificial pupils by measuring the effects of the pupil diameter (0.5-5 mm in range) and defocus (5-D myopia to 4-D hyperopia) on minimum angles of resolution (MARs) and on angular blur disk diameters. For pupil diameters down to ~ 2.0 mm there were no meaningful differences between the visual resolution that is obtained with the physical and the Maxwellian pupils. At the smallest diameter (0.5 mm) the physical artificial pupils caused the MAR to increase because of the diffraction limitation on resolution, and defocus no longer affected MAR. With the small Maxwellian pupils vision did not become diffraction-limited so that maximum resolution could still be obtained. MAR was still affected by defocus. The angular blur disk diameters measured with the smaller Maxwellian pupils were slightly but significantly larger than those found with physical artificial pupils. For physical artificial pupils, field-of-view restrictions may result from vignetting with the eye pupil. Thus small physical artificial pupils can act as pinholes causing resolution to become impaired but insensitive to defocus. Also vignetting by the eye pupil can restrict the field of view. Small optical artificial pupils from Maxwellian viewing do not impair resolution, and the resolution may remain sensitive to defocus. The eye pupil does not cause any field restriction, although, if small, it may filter higher spatial frequencies out of the retinal image.

Task performance and contrast polarity on hard copy and video displays

Performance was measured on an editing task which required counting the number of occurrences of an assigned letter in a paragraph of random letters. The task was presented in three different display modes: (a) a video display (VDT) with white characters on a black background, (b) a white-on-black photograph of the VDT display, and (c) a black-on--white photograph of the VDT task display. The viewing conditions for the three display modes were matched. Defocus was introduced by cylindrical lenses (simulated astigmatism) and by plus lenses. Performance was measured by time and accuracy in completing the counting task. There were 19 normally-sighted young adult subjects tested with the task in the three display modes under 6 levels of defocus. For the hard copy displays, performance was significantly faster (on average by 6.6%) for black characters on a white background. Performance with the black background photographs was consistently, but marginally (0.9%), faster than with the VDT displays. Cylindrical defocus of 1.50 diopters substantially impaired efficiency, but low-power plus lenses did not affect performance.

Effects of Font Size and Reflective Glare on Text-Based Task Performance and Postural Change Behavior of Presbyopic and Nonpresbyopic Computer Users

Nineteen young (18-35 year-old) and seven older presbyopic (55-65 year-old, wearing bifocal or progressive glasses) subjects with the same average visual acuity at near distance participated in this full-factorial, repeated measures study with two trial factors: font size (capital letter heights of 1.78, 2.23, and 3.56 mm) and reflective glare. The monitor location was fixed, but subjects were allowed to move their bodies and the chair while performing visually demanding tasks. The productivity improved up to 30% when using a large font size (average visual angle 23.4 arcmin) compared to a smaller font size (14.2 or 16.4 arcmin, p < .0001). The relative contributions of torso flexion (78%), head forward (3%), and chair reposition (4%) to changes in the viewing distance remained constant across font size conditions. Reflective glare had no effect on productivity measures but led to reduction of viewing distance (p < .0001). There were no significant differences between the two age groups.

Peripheral light-focusing: measurement reliability and correlations with ocular dimensions.

Purpose. When a beam of light is directed toward the temporal limbus from an angle of about 120° temporal to the primary line of sight, an illuminated patch appears on the sclera at the nasal limbus. An optical apparatus was developed for measuring the angular range of this optical phenomenon, often called the temporal catchment angle. It is possible that the temporal catchment angle or its correlates could serve as a key risk factor for the development of pterygia or cortical cataract. Methods. We built an apparatus that allows variation in the angle of a beam directed toward the temporal limbus. Two examiners measured the angular catchment range over which peripheral light focusing occurred for the right eyes of 30 subjects. Other anterior segment dimensions, including palpebral aperture height, refractive error, central and peripheral corneal power, anterior chamber depth, and corneal diameter, were measured. Results. There was no statistically or clinically significant difference between the repeated measures of the examiners. The mean temporal catchment angle was 17.1° (SD, 6.5). The intraobserver and interobserver 95% limits of agreement were 6.2 and 9.7°, respectively. The mean posterior limit was 121.0° (SD, 5.5), and the mean anterior limit was 104.1° (SD, 6.5) from the primary line of sight. The temporal catchment angle was positively correlated with central corneal power (R2 = 0.18; p = 0.02), peripheral corneal power (R2 = 0.18; p = 0.01), anterior chamber depth (R2 = 0.29; p = 0.002), and corneal diameter (R2 = 0.37; p = 0.002). Using multivariate linear regression analysis, we determined that central corneal power in the horizontal meridian and corneal diameter, in combination, best predicted the magnitude of the temporal catchment angle (R2 = 0.37; p = 0.0001). Conclusions. We have developed a reliable method of measuring the temporal catchment angle using a new head-mounted instrument. The temporal catchment angle was highly correlated with central corneal power and corneal diameter, in combination. The temporal catchment angle or its correlated ocular dimensions could be used to investigate risk factors for pterygia and cortical cataract.