Christine Dickinson

Waveform characteristics in congenital nystagmus

Using infra-red oculography, electro-oculography and fundus video-recordings, waveform characteristics (amplitude, frequency, waveform shape and foveation) were examined in over 150 individuals with congenital nystagmus. For many of the subjects the nystagmus exhibited marked variability in both space and time. The sources of this variability were explored and the state of attention of the observer was found to be a dominant factor. The waveform and precision of foveation were not found to be related to any one classification group (eg. albino or idiopathic).

Face recognition in age related macular degeneration: perceived disability, measured disability, and performance with a bioptic device.

Aims: (1) To explore the relation between performance on tasks of familiar face recognition (FFR) and face expression difference discrimination (FED) with both perceived disability in face recognition and clinical measures of visual function in subjects with age related macular degeneration (AMD). (2) To quantify the gain in performance for face recognition tasks when subjects use a bioptic telescopic low vision device. Methods: 30 subjects with AMD (age range 66–90 years; visual acuity 0.4–1.4 logMAR) were recruited for the study. Perceived (self rated) disability in face recognition was assessed by an eight item questionnaire covering a range of issues relating to face recognition. Visual functions measured were distance visual acuity (ETDRS logMAR charts), continuous text reading acuity (MNRead charts), contrast sensitivity (Pelli-Robson chart), and colour vision (large panel D-15). In the FFR task, images of famous people had to be identified. FED was assessed by a forced choice test where subjects had to decide which one of four images showed a different facial expression. These tasks were repeated with subjects using a bioptic device. Results: Overall perceived disability in face recognition did not correlate with performance on either task, although a specific item on difficulty recognising familiar faces did correlate with FFR (r = 0.49, p<0.05). FFR performance was most closely related to distance acuity (r = −0.69, p<0.001), while FED performance was most closely related to continuous text reading acuity (r = −0.79, p<0.001). In multiple regression, neither contrast sensitivity nor colour vision significantly increased the explained variance. When using a bioptic telescope, FFR performance improved in 86% of subjects (median gain = 49%; p<0.001), while FED performance increased in 79% of subjects (median gain = 50%; p<0.01). Conclusion: Distance and reading visual acuity are closely associated with measured task performance in FFR and FED. A bioptic low vision device can offer a significant improvement in performance for face recognition tasks, and may be useful in reducing the handicap associated with this disability. There is, however, little evidence for a correlation between self rated difficulty in face recognition and measured performance for either task. Further work is needed to explore the complex relation between the perception of disability and measured performance.

Head mounted video magnification devices for low vision rehabilitation: a comparison with existing technology

Patients with low vision typically have reduced visual acuity and a significant loss of contrast sensitivity, often in combination with visual field loss. These impairments cause a number of disabilities including difficulty with reading, writing, recognising faces, watching television, orientation and mobility, and completing activities of daily living. In a recent large scale survey of providers of low vision services, Elliott et al  1found that for elderly patients with low vision, the primary objectives identified at low vision assessment were to obtain help with reading and with vision oriented performance of daily living activities. Secondary objectives commonly include obtaining help with watching television, mobility and independent travel, and hobbies. In many cases, these objectives can be met by the prescription and use of conventional low vision aids (LVAs)—that is, optical devices providing magnification in order to compensate for reduced visual acuity, while contrast is maximised with local task lighting. LVAs are, unfortunately, highly task specific, and the patient may need several different aids to deal with a variety of identified requirements. Recently, however, alternative devices have been introduced which offer a number of distinct advantages over conventional LVAs in low vision rehabilitation. The purpose of this review is to describe these devices and to discuss both their current and future potential in comparison with existing technology. Contrary to early work suggesting that LVAs are often limited in their effectiveness,2 3 more recent studies indicate that low vision rehabilitation and the prescription of LVAs can offer considerable benefit to the visually impaired, with at least one device being used by between 80% and 91% of patients provided with an LVA.4-8 It is recognised, however, that some patients do not continue to use LVAs following their dispensing. While some users discontinue with an LVA because of a change …

CORNEAL TOPOGRAPHY OF HUMANS WITH CONGENITAL NYSTAGMUS

Abstract The refractive status of individuals with congenital nystagmus (albinos and idiopaths) has been examined. Our results indicate that there is a greater than normal incidence of high spectacle astigmatism. This is predominantly with‐the‐rule and corneal in origin (anterior surface). Partial neutralization by the against‐the‐rule residual astigmatism is frequent and does not differ significantly from that reported for normal populations. Topographical studies of the anterior cortical surface revealed that there was no significantly significantly difference in the mean shape factor values for the albino, idioparh and control populations. The aetiology of the astigmatism is discussed.

THE ELUCIDATION AND USE OF THE EFFECT OF NEAR FIXATION IN CONGENITAL NYSTAGMUS

Abstract— It has frequently been reported that the spontaneous ocular oscillation in congenital nystagmats is less intense for near viewing than during distance fixation. The reason for this effect was sought, and the influences of monocular adduction, convergence and accommodation acting separately and synergistically were assessed. The frequent assumption that nystagmus intensity (amplitude and frequency) is determined by convergence angle (either symmetrical or asymmetrical) was confirmed, and it was found that binocular viewing was not necessary. An identical effect on nystagmus intensity could be created for distance fixation by the use of base‐out prisms, and these were prescribed for constant wear in two congenital idiopathic nystagmats. Although nystagmus intensity was constantly reduced, no concomitant increase in binocular contrast sensitivity or Snellen visual acuity occurred.

Clinical impairment measures and reading performance in a large age-related macular degeneration group

Purpose. To investigate the relationship between clinical impairment measures and reading performance in a large population with age-related macular degeneration. Methods. The following clinical measures were evaluated on 243 patients with age-related macular degeneration: better eye distance visual acuity (ETDRS chart); threshold near word reading acuity (Bailey-Lovie Word Reading chart); maximum reading speed and critical print size (MNREAD chart); letter contrast sensitivity (Pelli-Robson); and kinetic perimetry (Bjerrum screen) to determine the nearest non-scotomatous point to fovea (NNPF; in degrees) and the central scotoma area (mm2). Results. Distance acuity correlated well to threshold near word acuity (r = 0.71), but word acuity was usually poorer. Critical print size was strongly related (p < 0.001) to near visual acuity (r2 = 0.31 and &bgr; = 0.47) and was poorer than threshold near word visual acuity by a mean difference of −0.41 (range, −1.10 to 0.34), which represents a mean acuity reserve of 2.5:1. On single regression, distance (p < 0.0001, r2 = 0.35, and &bgr; = −102.37) and near acuities (p < 0.0001, r2 = 0.52, &bgr; = −126.53), critical print size (p = 0.0001, r2 = 19, and &bgr; = 0.002), contrast sensitivity (p < 0.0001, r2 = 19, and &bgr; = 79.47), scotoma size (p = 0.006, r2 = 12, and &bgr; = −0.04), and NNPF (p = 0.001, r2 = 12, and &bgr; = −4.39) were all highly significantly related to reading speed although these predicted only a low percentage of variance. Best prediction of reading speed was obtained on multiple regression, where NNPF and near word acuity explained 60% of the variance (p < 0.0001). Conclusions. Optimal prediction of reading speed with clinical parameters appears to be based on the combination of near word acuity and scotoma area, explaining 60% of the variance. Other factors not measured in this study are likely to account for the rest of the prediction.

The inter-relationship between magnification, field of view and contrast reserve: the effect on reading performance

For the reading task, contrast reserve is defined as the ratio of the letter contrast of the printed letters, to the readers contrast threshold. Acuity reserve is the ratio of the print size used for the reading task, to the readers visual acuity. The effects of low contrast reserve on reading performance were investigated at various magnifications, ranging from 3x to 7.5x, with the field of view systematically controlled. Eye movements were recorded whilst normally sighted subjects read using the magnifiers. It was shown that with adequate contrast reserve, increasing the field of view improved the reading rate because of the resulting increase in forward saccade length. Conversely, reducing the contrast reserve slowed the reading rate by decreasing the length of forward saccades and increasing the mean fixation duration, suggesting that the perceptual span is reduced at low contrast reserve. This study also shows that when the contrast reserve is low, providing magnification higher than that required for letter recognition (that is, increasing the acuity reserve) will not improve the reading performance. Furthermore, even when the contrast reserve was high, reading rates were lower for the magnifications of 5x and higher, because increases in saccade length do not match those of the retinal image size at these magnifications.

Visual acuity and fixation characteristics in age-related macular degeneration.

Purpose. To compare “single letter” (SL) acuity, “crowded letter” (CL) acuity, and “repeated letter” (RL) acuity for patients with age-related macular degeneration (AMD) and investigate if differences between these visual acuities are associated with fixation characteristics. Methods. A total of 243 patients with AMD had their best-corrected visual acuity measured on an ETDRS chart. SL, CL, and RL acuities were measured using Landolt C targets on a monitor. Fifty-degree-field red-free fundus photographs were taken and a static target was used to calculate the Preferred Retinal Locus (PRL) distance and direction from the fovea. Quality of fixation (consistency and oculomotor response) was also assessed using a fundus camera and a dynamic target. Results. RL acuity was almost always better than CL acuity and SL acuity was almost always better than CL acuity. The mean (±SD) RL-CL and SL-CL acuity differences were −0.13 (±0.15) logMAR and −0.11 (±0.13) logMAR respectively. The median PRL distance was 3.73° and the preferred retinal areas for the location of the PRL were the left (left quadrant of visual field; 39.5% of cases) and superior (inferior quadrant of visual field; 25.4%). Visual acuity was significantly associated with PRL distance but PRL distance only explained 10% of the variation in visual acuity. PRL distance was found to be a significant but weak predictor of the SL-CL acuity difference but fixation quality was not a good predictor of the RL-CL acuity difference. Conclusions. Although the acuity measured under different stimulus conditions varies, the absolute differences are small. This suggests that these techniques would not be helpful in determining fixation characteristics, or predicting the outcome of rehabilitation in individual patients with AMD.

The effect of simulated visual impairment on speech-reading ability.

Citation information: Dickinson CM & Taylor JJ. The effect of simulated visual impairment on speech‐reading ability. Ophthalmic Physiol Opt 2011, 31, 249–257. doi: 10.1111/j.1475‐1313.2010.00810.x

Vision impairment and dual sensory problems in middle age

Vision and hearing impairments are known to increase in middle age. In this study we describe the prevalence of vision impairment and dual sensory impairment in UK adults aged 40–69 years in a very large and recently ascertained data set. The associations between vision impairment, age, sex, socioeconomic status, and ethnicity are reported.