Ahalya Subramanian

The repeatability of MNREAD acuity charts and variability at different test distances.

Purpose. The purposes of this study are to establish the repeatability of the MNREAD acuity charts in a normal adult population and to determine the coefficient of repeatability for reading acuity, reading speed, and critical print size. The study also investigates how changing the working distance affects these parameters. Methods. Thirty normal young adults (mean age, 23.3 years) participated. Test–retest repeatability was assessed at 40 cm over two sessions by the same examiner using MNREAD charts 1 and 2. Additional measurements were also carried out at 24 cm and 52 cm working distances. The distance and the version of the chart used were randomized. Results. The coefficient of repeatability was found to be ± 0.05 logarithm of the minimum angle of resolution (logMAR) for reading acuity, ± 0.12 logMAR for critical print size, and ± 8.6 words per minute for reading speed. Reading acuity and critical print size changed significantly with testing distance (p = 0.001). No changes were found in the reading speed at the different test distances (p = 0.27). Conclusions. The MNREAD acuity charts can be used reliably to measure reading acuity, reading speed, and critical print size in a normal adult population.

Reaching and grasping with restricted peripheral vision

Aim:  To investigate how prehensile movements, such as reaching and grasping, are affected by different fields of view when both haptic and visual information are available.

Repeatability of Reading Ability Indices in Subjects with Impaired Vision

PURPOSE Reading speed and acuity measurements are important means of evaluating reading performance in subjects with impaired vision. The MNREAD charts are gradually becoming a popular means of measuring reading ability in low-vision clinics; yet, to date there are no standards of reliability for the visually impaired population. The present study was conducted to determine the coefficients of repeatability for reading speed, reading acuity, and critical print size in a visually impaired population. METHODS Twenty-seven visually impaired subjects (19 women and 8 men; mean age, 72.07; SD, 12.79 years) participated. Test-retest repeatability of the MNREAD charts was assessed at the subjects preferred viewing distance over two sessions by the same examiner. RESULTS The coefficient of repeatability (CR) was found to be +/-0.10 logMAR for reading acuity, +/-0.20 logMAR for critical print size and +/-0.10 logarithm of words per minute for reading speed. The CR was not dependent on visual acuity. CONCLUSIONS As expected, the coefficients of repeatability are higher in visually impaired subjects than in normal subjects. Critical print size measurements have the poorest reliability and precision and should be interpreted with caution.

Target contrast affects reaching and grasping in the visually impaired subjects.

Purpose. The aim of this study is to investigate whether subjects with central visual impairment (VI) show different reaching and grasping behavior for targets of different contrasts compared with visually normal age-matched subjects. Methods. Reaching and grasping performance was measured in 14 subjects with VI and 14 normal subjects. Subjects were asked to pick up a cylindrical target. Three different targets were used: black (low contrast), white (high contrast), and transparent, placed against a black background. A motion analysis system (Vicon 460) recorded and reconstructed the hand and finger movements. Results. Significantly longer onset times, total movement duration, and time after maximum grip aperture were obtained for subjects with VI compared with normal subjects (p < 0.002). No significant differences existed in maximum velocity and grip aperture between the two groups for any of the targets. Conclusions. Subjects with VI took longer to initiate and to complete the movement. Maximum velocity and grip aperture were not different suggesting that once the target was “seen” by subjects with VI performance was similar to normal subjects. Time after maximum grip aperture was longer in subjects with VI indicating the need for “online” modifications in these subjects. Contrast sensitivity was significantly correlated to more indices than visual acuity.

Baseline MNREAD Measures for Normally Sighted Subjects From Childhood to Old Age

Purpose The continuous-text reading-acuity test MNREAD is designed to measure the reading performance of people with normal and low vision. This test is used to estimate maximum reading speed (MRS), critical print size (CPS), reading acuity (RA), and the reading accessibility index (ACC). Here we report the age dependence of these measures for normally sighted individuals, providing baseline data for MNREAD testing. Methods We analyzed MNREAD data from 645 normally sighted participants ranging in age from 8 to 81 years. The data were collected in several studies conducted by different testers and at different sites in our research program, enabling evaluation of robustness of the test. Results Maximum reading speed and reading accessibility index showed a trilinear dependence on age: first increasing from 8 to 16 years (MRS: 140–200 words per minute [wpm]; ACC: 0.7–1.0); then stabilizing in the range of 16 to 40 years (MRS: 200 ± 25 wpm; ACC: 1.0 ± 0.14); and decreasing to 175 wpm and 0.88 by 81 years. Critical print size was constant from 8 to 23 years (0.08 logMAR), increased slowly until 68 years (0.21 logMAR), and then more rapidly until 81 years (0.34 logMAR). logMAR reading acuity improved from −0.1 at 8 years to −0.18 at 16 years, then gradually worsened to −0.05 at 81 years. Conclusions We found a weak dependence of the MNREAD parameters on age in normal vision. In broad terms, MNREAD performance exhibits differences between three age groups: children 8 to 16 years, young adults 16 to 40 years, and middle-aged to older adults >40 years.

Are rehabilitation services for patients in UK eye clinics adequate? A survey of eye care professionals

PurposeThe purpose of this study is to determine whether specific services such as emotional and family support are currently available in the United Kingdom for people with visual impairment.MethodsA validated online survey was created and distributed to clinical staff in eye clinics (for example, ophthalmologists and optometrists) and rehabilitation staff (for example, social and rehabilitation workers) in the community, who worked with people with visual impairment. A total of 67 clinical and 42 rehabilitation staff completed the entire survey online.ResultsOnly 67% of the respondents claimed their clinics provide emotional support and 44% of respondent’s clinics provided family support. Clinical and rehabilitation staff have differences in opinion over what constitutes an essential service for a visually impaired patient. Rehabilitation staff considered emotional support and referral to social services as essential more often than clinical staff (P<0.05). There is some confusion over the type of personnel who provides each type of service, with some services showing substantial repetition.ConclusionIn the clinics sampled, there appears to be an underprovision of emotional support (attentive listening plus constructive suggestions) and family support (emotional support and advice for family members) for visually impaired patients in the United Kingdom. There also seems to be some discrepancy in services that eye care professionals feel are available and previous reports by visually impaired patients of the service they receive. There is a need to develop standardised pathways across the United Kingdom, to solve some of these issues.

Size constancy in visual impairment: a comparison with normally sighted individuals*

Size judgements are usually based on size constancy. However, as the number of visual cues decreases, such as by decreasing the field of view, size judgements gradually change from those based on size constancy to those based on the visual angle. The present study investigated whether visually impaired (VI) individuals, most of whom do not have measurable stereoacuity and have visual field defects, might therefore make judgements based on visual angle rather than size constancy. Size constancy was measured on 42 VI and 20 normally sighted subjects. Results indicated that size judgements are similar for both VI and normally sighted individuals at 0.50 m, 1 and 2 m. Statistically significant differences were found at 3 m. Despite this it would appear that VI individuals are able to make judgements based on size constancy rather than the visual angle.

Learning to read vertical text in peripheral vision.

Purpose English-language text is almost always written horizontally. Text can be formatted to run vertically, but this is seldom used. Several studies have found that horizontal text can be read faster than vertical text in the central visual field. No studies have investigated the peripheral visual field. Studies have also concluded that training can improve reading speed in the peripheral visual field for horizontal text. We aimed to establish whether the horizontal vertical differences are maintained and if training can improve vertical reading in the peripheral visual field. Methods Eight normally sighted young adults participated in the first study. Rapid serial visual presentation (RSVP) reading speed was measured for horizontal and vertical text in the central visual field and at 10 degrees eccentricity in the upper or lower (horizontal text) and right or left (vertical text) visual fields. Twenty-one normally sighted young adults split equally between two training groups and one control group participated in the second study. Training consisted of RSVP reading using either vertical text in the left visual field or horizontal text in the inferior visual field. Subjects trained daily over 4 days. Pre- and post- horizontal and vertical RSVP reading speeds were carried out for all groups. For the training groups, these measurements were repeated 1 week and 1 month posttraining. Results Before training, RSVP reading speeds were faster for horizontal text in the central and peripheral visual fields when compared with vertical text. Training vertical reading improved vertical reading speeds by an average factor of 2.8. There was partial transfer of training to the opposite (right) hemifield. The training effects were retained for up to a month. Conclusions Rapid serial visual presentation training can improve RSVP vertical text reading in peripheral vision. These findings may have implications for patients with macular degeneration or hemianopic field loss.

Is the Aligning Prism Measured with the Mallett Unit Correlated with Fusional Vergence Reserves

Background The Mallett Unit is a clinical test designed to detect the fixation disparity that is most likely to occur in the presence of a decompensated heterophoria. It measures the associated phoria, which is the “aligning prism” needed to nullify the subjective disparity. The technique has gained widespread acceptance within professions such as optometry, for investigating suspected cases of decompensating heterophoria; it is, however, rarely used by orthoptists and ophthalmologists. The aim of this study was to investigate whether fusional vergence reserves, measured routinely by both orthoptists and ophthalmologists to detect heterophoria decompensation, were correlated with aligning prism (associated phoria) in a normal clinical population. Methodology/Principal Findings Aligning prism (using the Mallett Unit) and fusional vergence reserves (using a prism bar) were measured in 500 participants (mean 41.63 years; standard deviation 11.86 years) at 40 cm and 6 m. At 40 cm a strong correlation (p<0.001) between base in aligning prism (Exo FD) and positive fusional reserves was found. Of the participants with zero aligning prism 30% had reduced fusional reserves. At 6 m a weak correlation between base out aligning prism (Eso FD) and negative fusional reserves was found to break (p = 0.01) and to recovery (p = 0.048). Of the participants with zero aligning prism 12% reported reduced fusional reserves. Conclusions/Significance For near vision testing, the strong inverse correlation between base in aligning prism (Exo FD) and fusional vergence reserves supports the notion that both measures are indicators of decompensation of heterophoria. For distance vision testing and for those patients reporting zero aligning prism further research is required to determine why the relationship appears to be weak/non-existent?

Acuity and colour vision changes post intravitreal dexamethasone implant injection in patients with diabetic macular oedema

Purpose To evaluate changes in colour vision following intravitreal injection of Dexamethasone implant (Ozurdex) in patients with diabetic macular oedema (DMO). Both red-green (RG) and yellow-blue (YB) chromatic sensitivity were assessed using the Colour Assessment & Diagnosis (CAD) test which isolates the use of colour signals and provides age-corrected, statistical limits for normal trichromats. To determine whether colour changes and visual acuity (VA) post-treatment relate to central sub-field retinal thickness (CST). Methods Fourteen patients with DMO who were undergoing treatment with Ozurdex were recruited for this study. RG and YB colour thresholds were measured using the CAD test, best corrected visual acuity was assessed using the ETDRS chart and CST was measured using spectral domain optical coherence tomography (SD-OCT). All tests were performed monocularly at baseline and 24 weeks post injection. Results All patients (n = 14 eyes), had significant loss of RG and YB chromatic sensitivity at baseline (p<0.05). The mean age was 56 ± 9.5 years. The age specific, monocular, upper normal limits for a 56 year old subject are 2.66 for RG and 2.85 for YB. In this study, the measured, pre injection thresholds (mean±SD) were 22.6 ± 11.3 for RG and 16.2 ± 3.76 for YB. There was significant improvement in RG threshold post injection (i.e., 19.2 ± 10.8 (p<0.05)). No significant changes were found in the YB thresholds with corresponding mean and range values of: 15.8 ± 4.6 (p = 0.23). CST pre-treatment was 542 ±135 μm. After treatment and by week 24 the CST values decreased to 435 ±127 μm. Conclusions RG colour thresholds provide a sensitive measure of functional change in diabetic subjects with macular oedema. The YB system is damaged severely in the DMO patients studied and shows little or no recovery post treatment. The improvement in VA and particularly in RG colour vision correlate well with the measured decrease in CST. The results suggest that the improvement in the RG chromatic sensitivity can provide a useful biomarker for monitoring the efficacy of treatment in DMO.