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PubMed1993

Outcomes of cataract surgery. Improvement in visual acuity and subjective visual function after surgery in the first, second, and both eyes.

OBJECTIVE: No previous study documents improvement in visual acuity and subjective visual function associated with cataract surgery in the first eye, second eye, and both eyes. Measurement of subjective aspects of visual function and quality of life provides information that cannot be obtained with simple measurement of Snellen visual acuity. METHODS: From 76 ophthalmology practices in three cities, patients undergoing cataract extraction with intraocular lens implantation (n = 613) and comparison patients (n = 408) were enrolled in a prospective study. Questionnaires elicited visual function information before and after surgery, and visual acuity was obtained from the ophthalmologic record. RESULTS: Among patients with cataract and no other eye disease, baseline subjective visual function before surgery in the second eye was better than that before surgery in the first eye. Improvement in subjective visual function was approximately equal postoperatively in first and second eyes. Improvement in subjective function in both eyes postoperatively was significantly greater than that after surgery in the first eye or second eye alone. No statistically significant difference across surgical groups in the proportion of patients demonstrating improvement in visual acuity was observed. CONCLUSION: Patients who underwent surgery in both eyes reported greater improvement in subjective visual function than did those who underwent surgery in one eye. Thus, there seems to be a benefit associated with restoring binocular vision in this population. These findings support the policy recommendation that cataract surgery in both eyes remains the appropriate treatment for patients with bilateral, cataract-induced visual impairment.

Aged↗
PubMed2001

Cortical activation during Braille reading is influenced by early visual experience in subjects with severe visual disability: a correlational fMRI study.

Functional magnetic resonance imaging was performed on blind adults resting and reading Braille. The strongest activation was found in primary somatic sensory/motor cortex on both cortical hemispheres. Additional foci of activation were situated in the parietal, temporal, and occipital lobes where visual information is processed in sighted persons. The regions were differentiated most in the correlation of their time courses of activation with resting and reading. Differences in magnitude and expanse of activation were substantially less significant. Among the traditionally visual areas, the strength of correlation was greatest in posterior parietal cortex and moderate in occipitotemporal, lateral occipital, and primary visual cortex. It was low in secondary visual cortex as well as in dorsal and ventral inferior temporal cortex and posterior middle temporal cortex. Visual experience increased the strength of correlation in all regions except dorsal inferior temporal and posterior parietal cortex. The greatest statistically significant increase, i.e., approximately 30%, was in ventral inferior temporal and posterior middle temporal cortex. In these regions, words are analyzed semantically, which may be facilitated by visual experience. In contrast, visual experience resulted in a slight, insignificant diminution of the strength of correlation in dorsal inferior temporal cortex where language is analyzed phonetically. These findings affirm that posterior temporal regions are engaged in the processing of written language. Moreover, they suggest that this function is modified by early visual experience. Furthermore, visual experience significantly strengthened the correlation of activation and Braille reading in occipital regions traditionally involved in the processing of visual features and object recognition suggesting a role for visual imagery.

Adult↗
PubMed2003

Visual acuity testing in diabetic subjects: the decimal progression chart versus the Freiburg visual acuity test.

PURPOSE: To study reproducibility and biological variation of visual acuity in diabetic maculopathy, using two different visual acuity tests, the decimal progression chart and the Freiburg visual acuity test. METHODS: Twenty-two eyes in 11 diabetic subjects were examined several times within a 12-month period using both visual acuity tests. The most commonly used visual acuity test in Denmark (the decimal progression chart) was compared to the Freiburg visual acuity test (automated testing) in a paired study. RESULTS: Correlation analysis revealed agreement between the two methods (r(2)=0.79; slope=0.82; y-axis intercept=0.01). The mean visual acuity was found to be 15% higher (P<0.0001) with the decimal progression chart than with the Freiburg visual acuity test. The reproducibility was the same in both tests (coefficient of variation: 12% for each test); however, the variation within the 12-month examination period differed significantly. The coefficient of variation was 17% using the decimal progression chart, 35% with the Freiburg visual acuity test. CONCLUSION: The reproducibility of the two visual acuity tests is comparable under optimal testing conditions in diabetic subjects with macular oedema. However, it appears that the Freiburg visual acuity test is significantly better for detection of biological variation.

Adult↗
PubMed2002

Visual cortex excitability increases during visual mental imagery--a TMS study in healthy human subjects.

Previous neuroimaging studies provided evidence that visual mental imagery relies, in part, on the primary visual cortex. We hypothesized that, analogous to the finding that motor imagery increases the excitability of motor cortex, visual imagery should increase visual cortex excitability, as indexed by a decrease in the phosphene threshold (PT). In order to test visual cortex excitability, the primary visual cortex was stimulated with transcranial magnetic stimulation (TMS), so as to elicit phosphenes in the right lower visual quadrant. Subjects performed a visual imagery task and an auditory control task. We applied TMS with increasing intensity to determine the PT for each subject. Independent of the quadrant in which subjects placed their visual images, imagery decreased PT compared to baseline PT; in contrast, the auditory task did not change PT. These findings demonstrate for the first time a short-term, task-dependent modulation of PT. These results constitute evidence that early visual areas participate in visual imagery processing.

Adult↗
PubMed2002

Correlation between visual function and visual ability in patients with uveitis.

AIM: To investigate the correlation between tests of visual function and perceived visual ability recorded with a quality of life questionnaire for patients with uveitis. METHODS: 132 patients with various types of uveitis were studied. High (monocular and binocular) and low (binocular) contrast logMAR letter acuities were recorded using a Bailey-Lovie chart. Contrast sensitivity (binocular) was determined using a Pelli-Robson chart. Vision related quality of life was assessed using the Vision Specific Quality of Life (VQOL) questionnaire. RESULTS: VQOL declined with reduced performance on the following tests: binocular high contrast visual acuity (p = 0.0011), high contrast visual acuity of the better eye (p = 0.0012), contrast sensitivity (p = 0.005), binocular low contrast visual acuity (p = 0.0065), and high contrast visual acuity of the worse eye (p = 0.015). Stepwise multiple regression analysis revealed binocular high contrast visual acuity (p <0.01) to be the only visual function adequate to predict VQOL. The age of the patient was also significantly associated with perceived visual ability (p <0.001). CONCLUSIONS: Binocular high contrast visual acuity is a good measure of how uveitis patients perform in real life situations. Vision quality of life is worst in younger patients with poor binocular visual acuity.

Adolescent↗
PubMed2005

Use of visual information in speech perception: evidence for a visual rate effect both with and without a McGurk effect.

The McGurk effect, where an incongruent visual syllable influences identification of an auditory syllable, does not always occur, suggesting that perceivers sometimes fail to use relevant visual phonetic information. We tested whether another visual phonetic effect, which involves the influence of visual speaking rate on perceived voicing (Green & Miller, 1985), would occur in instances when the McGurk effect does not. In Experiment 1, we established this visual rate effect using auditory and visual stimuli matching in place of articulation, finding a shift in the voicing boundary along an auditory voice-onset-time continuum with fast versus slow visual speech tokens. In Experiment 2, we used auditory and visual stimuli differing in place of articulation and found a shift in the voicing boundary due to visual rate when the McGurk effect occurred and, more critically, when it did not. The latter finding indicates that phonetically relevant visual information is used in speech perception even when the McGurk effect does not occur, suggesting that the incidence of the McGurk effect underestimates the extent of audio-visual integration.

Adolescent↗
PubMed2006

Visual hallucinations during visual recovery after central retinal artery occlusion.

BACKGROUND: Charles Bonnet syndrome is characterized by complex, formed visual hallucinations that occur in patients without psychiatric disorders. To the best of our knowledge, it has not been described following central retinal artery occlusion. OBJECTIVE: To describe 2 patients who experienced formed visual hallucinations characteristic of Charles Bonnet syndrome after sudden, severe visual loss precipitated by central retinal artery occlusion. PATIENTS: Two patients, aged 77 and 63 years respectively, experienced sudden deterioration of vision following central retinal artery occlusion. Formed visual hallucinations occurred in patient 1 six days later and in patient 2 two days later. RESULTS: The hallucinations appeared both within and at the borders of the patients' residual intact visual fields. They occurred during periods when the patients experienced partial visual recovery associated with enlargement of their visual fields. The visual recovery and hallucinations both ceased at the same time. CONCLUSIONS: We propose that the hallucinations are likely the result of deafferentation and their occurrence during visual recovery suggests that they are a correlate of visual system plasticity.

Aged↗
PubMed2005

Multifocal visual evoked potential in nonorganic visual field loss.

OBJECTIVE: To evaluate the use of multifocal visual evoked potentials in the diagnosis of nonorganic visual field loss. METHODS: Five patients with unexplained visual field loss underwent full neuro-ophthalmic examination, Humphrey visual field testing, and multifocal visual evoked potential testing using the Accumap objective perimeter (ObjectiVision Pty Ltd, Sydney, Australia). RESULTS: In all 5 cases, the results of the ophthalmic examination did not correlate with the degree of visual field loss seen on Humphrey visual field testing. Multifocal visual evoked potentials testing showed essentially normal tracings. CONCLUSIONS: Multifocal visual evoked potentials may be useful in cases of difficult to prove functional visual field loss or in cases in which objective documentation of normal function is needed.

Adolescent↗
PubMed1996

Detection of visual dysfunction in optic atrophy by functional magnetic resonance imaging during monocular visual stimulation.

PURPOSE: To evaluate functional magnetic resonance imaging as an objective method for detecting visual dysfunction in various ophthalmologic disorders involving the optic nerve and the chiasm. METHODS: We performed functional magnetic resonance imaging during monocular visual stimulation on seven patients with visual field loss caused by lesions of the optic nerve and the chiasm and on three normal control subjects with no visual field loss. We correlated static threshold perimetry in the seven patients with the results of functional magnetic resonance imaging. RESULTS: In the three normal control subjects, we found good intrasubject similarity in areas of bilateral occipital lobe activation between monocular stimulation of the right and left eyes. In the patients with unilateral optic neuropathy, including glaucoma, stimulation of the affected eye induced no activation of the primary visual cortex in the portion corresponding to the central visual field defects and reduced activity of the associated visual cortex. In the patients with chiasmal compression, monocular stimulation resulted in a marked asymmetry of activation in the primary visual cortex, which corresponded to the visual field abnormality. CONCLUSIONS: Functional magnetic resonance imaging appears to be useful in confirming the clinical diagnosis of optic atrophy because it can objectively disclose visual field loss, even a small defect such as central scotoma.

Adult↗
PubMedDate not supplied

Lack of short-latency-potentials in the VEP reflects immature extra geniculate visual function in delayed visual maturation (DVM).

PURPOSE: To investigate children with delayed visual maturation (DVM) and correlate the electrophysiological findings to visual development. METHODS: Three children, one from each of the DVM-classification groups, were subjected to routine ophthalmological examinations and electrophysiological examinations: flash visual evoked potential (VEP) and skin electrode electroretinography (ERG). RESULTS: All three children had normal ERGs but initially abnormal VEP-recordings with marked delay of latency or grossly altered VEPs. When visual interest developed with responsive smiling at 4, 4.5 and approximately 12 months of age, a maturation in the VEPs also appeared, with development of a short-latency complex (approximately 70 ms). In the normal neonatal development of the VEP, a negativity at approximately 60-70 ms (N1) emerged at four to six weeks of postnatal life when the child started responsive smiling and showing raised visual interest. According to animal experimental research and human studies, the development of the specific response (the short-latency complex) represents the gradual onset of cortical activity mediated via the specific retino-geniculo-striatal pathway. Thus, when the short-latency complex of the VEP cannot be identified, the visual function is mainly of subcortical origin. Since the VEP developed in the same way in the children with DVM as in normal subjects, the pathophysiological dysfunction and origins of DVM can partly be understood. CONCLUSIONS: The results show that i) children with DVM has a period of visual inattentiveness at a time when normal children show visual interest, ii) the VEP is abnormal in children with DVM at the time of visual inattentiveness, iii) the improvement of vision in DVM can be measured with VEP and iiii) the extra-geniculate system(s) provides for the visual function early neonatally in the normal child and in a prolonged period in the DVM-child as long as the VEPs are abnormal.

Electroretinography↗
PubMed2006

Imprinting modulates processing of visual information in the visual wulst of chicks.

BACKGROUND: Imprinting behavior is one form of learning and memory in precocial birds. With the aim of elucidating of the neural basis for visual imprinting, we focused on visual information processing. RESULTS: A lesion in the visual wulst, which is similar functionally to the mammalian visual cortex, caused anterograde amnesia in visual imprinting behavior. Since the color of an object was one of the important cues for imprinting, we investigated color information processing in the visual wulst. Intrinsic optical signals from the visual wulst were detected in the early posthatch period and the peak regions of responses to red, green, and blue were spatially organized from the caudal to the nasal regions in dark-reared chicks. This spatial representation of color recognition showed plastic changes, and the response pattern along the antero-posterior axis of the visual wulst altered according to the color the chick was imprinted to. CONCLUSION: These results indicate that the thalamofugal pathway is critical for learning the imprinting stimulus and that the visual wulst shows learning-related plasticity and may relay processed visual information to indicate the color of the imprint stimulus to the memory storage region, e.g., the intermediate medial mesopallium.

Animals↗
PubMed1979

Neurophysiological mechanisms of recovery from visual cortex damage in cats: properties of lateral suprasylvian visual area neurons following behavioral recovery.

Damage to visual cortical areas 17, 18, and 19 in the cat produces severe and long-lasting deficits in performance of form and pattern discriminations. However, with extensive retraining the animals are able to recover their ability to discriminate form and pattern stimuli. Recent behavioral experiments from this laboratory have shown that a nearby region of cortex, the lateral suprasylvian visual area (LS area), plays an important role in this recovery (Wood et al., 1974; Baumann and Spear, 1977b). The present experiment investigated the underlying neurophysiological mechanisms of the recovery by recording from single neurons in the LS area of cats which had recovered from long-term visual cortex damage. Five adult cats received bilateral removal of areas 17, 18, and 19. They were then trained to criterion on two-choice brightness, form, and pattern discriminations. Recording from LS area neurons was carried out after the behavioral training, from 3 to 7 months after the visual cortex lesions. The properties of these neurons were compared to those of LS area neurons in normal cats (Spear and Baumann, 1975) and in cats with acute or short-term visual cortex damage and no behavioral recovery (Spear and Baumann, 1979). The results showed that all of the changes from normal which were produced by acute visual cortex damage were also present after the behavioral recovery. Moreover, all of the response properties of LS area neurons which remain after acute visual cortex damage were present in similar form after the behavioral recovery. There was no evidence for any functional reorganization in the LS area concomitant with its role in the behavioral recovery. These results suggest that functional reorganization plays little or no role in recovery from visual cortex damage in adult cats. Rather, the recovery of form and pattern discrimination ability appears to be based upon the functioning of residual neural processes in the LS area which remain after the visual cortex damage.

Animals↗
PubMed2006

Visual impairments in people with severe and profound multiple disabilities: an inventory of visual functioning.

BACKGROUND: The prevalence of visual impairments in people with severe and profound multiple disabilities (SPMD) is the subject of considerable debate and is difficult to assess. METHODS: In a typical Dutch care organization, all clients with SPMD (n = 76) participated in the study and specific instruments adapted to these clients (requiring a minimum of cooperation) were used to measure visual acuity, the visual field, binocular vision, contrast sensitivity, refractive errors and visual functioning behaviour. RESULTS: We found an unexpected 92% of clients with SPMD to have visual impairments. Previously, only 30% were known to have visual problems. None of the persons observed had normal visual acuity. Subnormal visual acuity was the best result. The severity of the visual impairment was related to the severity of the intellectual disability. In addition to the problem of acuity, impairments in the visual field, impaired contrast sensibility and impaired binocular functioning were found, as well as impaired visual attention, fixation and following. In 22% of the clients observed, refractive errors were found and glasses were advised. CONCLUSIONS: Consequences for caregiving and for modifications of the environment were discussed.

Adolescent↗
PubMed1996

Visually guided stepping under conditions of step cycle-related denial of visual information.

We recently reported that subjects performing a task that requires visual guidance of each step onto irregularly placed "stepping stones" usually fixate the next target of footfall just before they lift the foot to be repositioned, i.e. towards the end of that limb's stance phase. When negotiating the same walkway without ambient lighting, and with each stone's location indicated by a central light spot (LED), stepping and eye movements were unchanged. Under conditions of intermittent visual denial, in which all LEDs (the only visual cues) were temporarily extinguished at irregular intervals, temporal changes in the normal stepping pattern were sometimes observed, but stepping was not always affected. The primary effect of visual denial was on the leg that was in stance (foot in place on a stepping stone) at the moment of LED extinction, rather than on the leg that was in swing, and was an increase in stance duration, suggesting an effect on planning during this stance of the next swing towards the next target rather than on execution of the ongoing swing of the other leg. Subjects rarely failed to step onto the targets. Prolongations of stance under visual denial lasting 400 or 500 ms were less than 200 ms, much less than the duration of denial; subjects did not simply wait for the footfall target to reappear. There was no effect for denial lasting 300 ms; subjects performed as well as with a constantly visible target. Under 400 and 500 ms denial, there was no effect when the targets disappeared in the first 100 ms of stance (of the foot to be repositioned); stance durations were indistinguishable from control. This suggests that there is no crucial visuomotor processing by the control system(s) for eye and limb guidance until the target reappeared near the usual end of stance, when feedforward planning of the next saccade and/or swing to a target reaches a crucial stage, and is affected by intrusion of the period of visual denial. With longer (800 ms) denial there was an effect regardless of when in stance it began. A smaller effect of 800 ms denial sometimes visible in swing duration is attributable to interlimb coordination. Accurate saccades, followed by accurate steps, to the next target are almost always made, even when the target is invisible. Our results demonstrate that uninterrupted on-line visual information is not necessary for accurate stepping even when (as here) each step requires visual guidance. Also, since stance prolongations did not always result, and they were always much shorter than the periods of denial, we conclude that the visuomotor control mechanism(s) are robust in the face of substantial denial of all visual information including normally preferred inputs (foveal or peripheral images) at the normally preferred times. The fact that a saccade is still made to an invisible target location implies that this is useful in itself, since it does not result in a visible foveal image. We propose that skilled, visually guided stepping onto irregularly placed targets is executed under predominantly feedforward visuomotor control mechanisms, and suggest that the ability to function effectively in this way is dependent upon the integrity of the lateral cerebellum.

Adult↗
PubMed1992

Simulation of a phosphene-based visual field: visual acuity in a pixelized vision system.

A visual prosthesis for the blind using electrical stimulation of the visual cortex will require the development of an array of electrodes. Passage of current through these electrodes is expected to create a visual image made up of a matrix of discrete phosphenes. The quality of the visual sense thus provided will be a function of many parameters, particularly the number of electrodes and their spacing. We are conducting a series of psychophysical experiments with a portable "phosphene" simulator to obtain estimates of suitable values for electrode number and spacing. The simulator consists of a small video camera and monitor worn by a normally sighted human subject. To simulate a discrete phosphene field, the monitor is masked by an opaque perforated film. The visual angle subtended by images from the masked monitor is 1.7 degrees or less, depending on the mask, and falls within the fovea of the subject. In the study presented here, we measured visual acuity as a function of the number of pixels and their spacing in the mask. Visual acuity was inversely proportional to pixel density, and trained subjects could achieve about 20/26 visual acuity with a 1024 pixel image. We conclude that 625 electrodes implanted in a 1 cm by 1 cm area near the foveal representation of the visual cortex should produce a phosphene image with a visual acuity of approximately 20/30. Such an acuity could provide useful restoration of functional vision for the profoundly blind.

Blindness↗
PubMed1995

The spatiotemporal organization of auditory, visual, and auditory-visual evoked potentials in rat cortex.

Four placements of an 8 x 8 channel microelectrode array were used to map auditory, visual, and combined auditory-visual evoked potentials (AEP, VEP, AVEP) from a total of 256 electrode sites over a 7 x 7 mm2 area including most of somatosensory, auditory, and visual cortex in the right hemisphere of the rat. The unimodal AEP and VEP consisted of an archetypal response sequence representing a systematic spatial and temporal activation of primary and secondary sensory cortex. Spatiotemporal analysis of these waveforms indicated that they could be decomposed into a small number of spatial and temporal components; components that are related to patterns of specific and non-specific thalamocortical projections connecting the auditory and visual nuclei of the thalamus with primary and secondary auditory and visual cortex. These data suggest that the AEP and VEP complex are the cortical reflection of asynchronous activation of parallel thalamocortical projection systems. The areal distribution of the AEP and VEP also overlapped, primarily in secondary auditory and visual cortex, indicating that these regions contain populations of cells responding to either modality. Polymodal auditory-visual stimulation resulted in unique activation of two isolated populations of neurons positioned in secondary auditory and secondary visual cortex which were revealed by difference waveforms, computed by subtracting the sum of the AEP and VEP from the AVEP complex. Retrograde labeling of the polymodal zones indicated that they receive parallel thalamocortical projections primarily from non-specific auditory and visual thalamic nuclei including the medial and dorsal divisions of the medial geniculate nucleus (MGm and MGd), the suprageniculate nucleus (SGN), and the lateral posterior nucleus (LP). The polymodal zone in visual cortex also receives specific projections from the dorsal division of the lateral geniculate nucleus (LGd). These data conform to a general model of thalamocortical organization in which specific thalamic nuclei with a high degree of modality specificity make restricted projections to primary sensory cortex and parts of secondary sensory cortex, and association thalamic nuclei with a high degree of sensory convergence make more divergent cortical projections. Primary and secondary sensory cortex, as well as distinct zones of polysensory cortex appear to be activated in tandem via parallel thalamocortical projections. Thus, the cerebral cortex must have simultaneous access to both unimodal and polymodal sensory information.

Animals↗
PubMed2005

A nationwide population-based survey on visual acuity, near vision, and self-reported visual function in the adult population in Finland.

PURPOSE: To estimate the prevalence rates of habitual visual acuity (VA) levels and visual impairment in Finland and to assess their correlation with self-reported visual function. DESIGN: Cross-sectional population-based study. PARTICIPANTS: Subjects were selected randomly from the Finnish population aged 30 years or older. Of 7979 eligible people, 7393 (93%) were interviewed, 6771 (85%) were examined, and 6663 (84%) had distance VA assessed. METHODS: Participants underwent a home interview and a comprehensive examination including measuring binocular VA for distance and for near with the participants' current spectacles, if any. MAIN OUTCOME MEASURES: The level of VA for distance and for near with current spectacle correction. The self-reported capability to read newsprint and television text and the ability to move about without being restricted by reduced vision. RESULTS: The prevalence of good to moderate VA for distance (VA> or =0.5 [> or =20/40]) measured with current spectacles was 95.9%, and 87.4% had a VA level of 0.8 (20/25) or better. The prevalence of habitual visual impairment (VA< or =0.25 [< or =20/80]) was 1.6%, and 0.5% were blind (VA<0.1 [<20/200]). The prevalence of visual impairment increased significantly with age (P<0.001), especially in the age group of 65 to 74 years and upward. There was no gender difference in VA for distance, but decreased near vision (VA< or =0.25 [< or =20/80]) was significantly more common in men than in women (P<0.01). By applying the imputated numbers of visually impaired and blind participants to the Finnish population (approximately 3 million aged 30 years or older), there were approximately 65000 (2.1%) visually impaired and 17000 (0.6%) blind adult persons in the country in 2000. The correlation between self-reported visual ability and measured visual function was moderate but statistically significant (r = 0.27-0.40; P<0.0001). The proportion of people with reading difficulties or who were unable to read newsprint has decreased 7% during the last 2 decades. CONCLUSIONS: Functional visual impairment increased with age especially in the age group of 65 to 74 years and upward and was as prevalent in women as in men. The prevalence of people with reading difficulties has decreased considerably since 1980.

Adult↗
PubMed2005

The effect of relative distance enlargement on visual acuity in the visually impaired.

BACKGROUND: Prescribing magnification is typically based on distance or near visual acuity. This presumes a constant minimum angle of visual resolution with working distance and therefore enlargement of an object moved to a shorter working distance (relative distance enlargement). This study examines this premise in a visually impaired population. METHODS: Distance letter visual acuity was measured prospectively for 380 low vision patients (distance visual acuity between 0.3 and 2.1 logMAR) over the age of 57 years, along with near word visual acuity at an appropriate distance for near lens additions from +4 D to +20 D. Demographic information, the disease causing low vision, contrast sensitivity, visual field and psychological status were also recorded. RESULTS: Distance letter acuity was significantly related to (r = 0.84) but on average 0.1 +/- 0.2 logMAR better (1 +/- 2 lines on a logMAR chart) than near word acuity at 25 cm with a +4 D lens addition. In 39.8 per cent of patients, near word acuity was more than 0.1 logMAR worse than distance letter acuity. In 11.0 per cent of subjects, near visual acuity was more than 0.1 logMAR better than distance letter acuity. The group with near word acuity worse than distance letter acuity also had lower contrast sensitivity. The group with near word acuity better than distance letter acuity was less likely to have age-related macular degeneration. Smaller print size could be read by reducing working distance (achieved by using higher near lens additions) in 86.1 per cent, although not by as much as predicted by geometric progression in 14.5 per cent. DISCUSSION: Although distance letter and near word acuity are highly related, they are on average 1 logMAR line different and this varies significantly between individuals. Near word acuity did not increase linearly with relative distance enlargement in approximately one in seven visually impaired, suggesting that the measurement of visual resolution over a range of working distances will assist appropriate prescribing of magnification aids.

Aged↗