The incidence of visually impaired drivers seen in ophthalmologic consultation

On the basis of a critical review by Dr. rer. nat. Bresser the calculation contained in the paper "Ophthalmological Experiences with Automobile Drivers with Inadequate Visual Acuity" is corrected. From the information on visits to the ophthalmologist contained in the study data, the average frequency of repeated visits can be worked out to 1.56. As a consequence, the average duration of unsuitable vision is 22.1 months. This results in a prevalence P = 360750. However, this figure can only apply to drivers who visit an ophthalmologist. According to a recent study based on a random sample of the population, the true number of drivers with unsuitable vision seems to be more than 4 times the figure quoted.     

Exercise-induced transient visual events in young healthy adults

Six patients with a variety of exercise-induced transient visual events are described. Each patient was in excellent health and most exercised regularly. None of the patients had a history of migraine, and only one gave a history of migraine in the family. One patient reported a single event, and the others reported recurrent events. These recurrent visual events were stereotyped except in one patient who experienced two distinctly different visual phenomena. Two patients described classic scintillating scotomas. Two described flickering phenomena in the central vision. Three described monocular events: one reported central scotomas, another blurring in the temporal field, and the third reported amaurosis. In no case could it be established that these events were associated with underlying disease. We believe that exercise-induced migraine equivalents are the most plausible explanation for these transient visual symptoms.     

Comparison of driving performance of young and old drivers (with and without visual impairment) measured during in-traffic conditions.

PURPOSE: The aim of this study was to determine whether visual impairment and age affected driver performance and safety rated during in-traffic driving conditions. METHODS: Participants included 30 younger, 25 middle-aged, and 35 older subjects with normal vision and 47 older subjects with visual impairment. All subjects were legally eligible to drive. Driving performance was assessed during in-traffic conditions by a professional driving instructor and an occupational therapist using specific scoring criteria. RESULTS: Group allocation significantly affected driving performance as assessed by the driving instructor and occupational therapist (p < 0.05). The driving instructor and occupational therapist scores were highly correlated (r = 0.76). Of the drivers who were scored as being unsafe, all were older and the majority (75%) had visual impairment. DISCUSSION: Older drivers with or without visual impairment were rated as being less safe than the younger and middle-aged drivers with normal vision.     

The effects of prolonged dark exposure on visual thresholds in young and adult rats.

A comparison of electroretinogram (ERG) thresholds measured on rats reared in continuous darkness and under cyclic lighting conditions shows that by 30 days of age the dark-reared animals have achieved significantly lower thresholds than the animals reared under cyclic illumination. Ten days of continuous dark exposure produces this same increase in sensitivity in adult rats reared in cyclic lighting. These changes in sensitivity appear to reflect structural changes occurring within the rod outer segments.     

Causes of severe visual impairment and blindness in schools for visually handicapped children in Iran

AIMS: This survey was conducted on children in schools for the blind in Tehran (from 2002 to 2003) to determine the causes of severe visual impairment and blindness and to identify preventable and treatable conditions. METHODS: The study was performed on 362 students at different grades in three schools for the blind. Patient sex, age, family history of blindness or low vision, visual acuity, causes of blindness, and treatable and preventable conditions were studied. RESULTS: Of the 362 cases, 210 (58%) were boys and 152 (42%) were girls. Mean age was 13.5 (SD 4) years. Severe visual loss was seen in 80.9%. Retinal diseases were the most common cause for low vision (51%); cataract, optic nerve atrophy, corneal and anterior segment diseases, glaucoma, anophthalmia, and globe malformations were other major causes of blindness. Treatable aetiologies and positive family history of blindness were seen in 25.7% and 36% of the patients, respectively. The incidence of preventable diseases, excluding familial disorders, was low. CONCLUSION: In addition to the prevention and treatment of some conditions, premarital genetic counselling and family planning control in families with inherited diseases could decrease the number of blind children in the future in Iran.     

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 aculty 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.     

Relationships between feature search and mobility performance in persons with severe visual impairment.

PURPOSE: Because visual search requires both the ability to discriminate visual features and the ability to process information in a large field of view, the association between feature search and mobility of visually impaired (VI) subjects was studied. METHODS: Forty-four subjects with severe visual impairment participated in the study. Feature search performance (2 x 2 deg square target amid 1 x 1 deg square distracters) was measured for 8- to 16- and 32-item set-sizes on 10 x 10, 20 x 20, and 40 x 40 deg fields. Mobility was evaluated on indoor high-density obstacle courses under photopic and mesopic illumination. RESULTS: In feature search, VI subjects were slower and made more errors than normal subjects, but they searched in a parallel fashion. On the mobility task, VI subjects walked slower and made more obstacle contacts than age-matched normal controls. In VI subjects, performances on feature search and mobility tasks were significantly associated, with 37.5% to 66.9 of variations in the mobility measurements being accounted for by visual search speed. CONCLUSIONS: Feature search reaction time can be a good predictor of VI patients' mobility.     

Causes of severe visual impairment and blindness in children attending schools for the visually handicapped in the Czech Republic

AIMS: To describe the causes of severe visual impairment and blindness in children in schools for the visually handicapped in the Czech Republic in 1998. METHODS: Pupils attending all 10 primary schools for the visually handicapped were examined. A modified WHO/PBL eye examination record for children with blindness and low vision was used. RESULTS: 229 children (146 males and 83 females) aged 6-15 years were included in the study: 47 children had severe visual impairment (20.5%) (visual acuity in their better eye less than 6/60), and 159 were blind (69.5%) (visual acuity in their better eye less than 3/60). Anatomically, the most affected parts of the eye were the retina (124, 54.2%), optic nerve (35, 15.3%), whole globe (25, 10.9%), lens (20, 8.7%), and uvea (12, 5.2%). Aetiologically (timing of insult leading to visual loss), the major cause of visual impairment was retinopathy of prematurity (ROP) (96, 41.9 %), followed by abnormalities of unknown timing of insult (97, 42.4%), and hereditary disease (21, 9.2%). In 90 children (40%), additional disabilities were present: mental disability (36, 16%), physical handicap (16, 7%), and/or a combination of both (19, 8%). It was estimated that 127 children (56%) suffer from visual impairment caused by potentially preventable and/or treatable conditions (for example, ROP, cataract, glaucoma). CONCLUSIONS: Establishing a study group for comprehensive evaluation of causes of visual handicap in children in the Czech Republic, as well as for detailed analysis of present practice of screening for ROP was recommended.     

The effects of severe keratitis on corneal transmission.

An investigation into the effects of keratitis on corneal light transmission is presented. Transmission data from 9 diseased corneas are compared to those of 22 normal corneas in the 0.3-0.8 micron spectral range. Rhesus monkey corneas were used in the study. Several color photographs illustrate varieties of idiopathic keratitis in rhesus monkeys.     

Mechanisms of visual loss in severe proptosis.

Vision loss in orbital hypertension secondary to sudden space-occupying lesions is usually attributed to one of three causes: central retinal artery occlusion, direct compressive optic neuropathy, or compression of optic nerve vasculature. Accepted modes of decompressive therapy include lateral canthotomy and cantholysis; drainage of localized orbital air, hematoma, or abscess; and bony wall decompression. Five cases are presented in which orbital hypertension caused severe proptosis with traction on the optic nerve and tenting of the posterior globe. Another mechanism contributing to visual loss is proposed in these cases: ischemic optic neuropathy due to stretching of nutrient vessels. In these cases, rapid posterior decompression should theoretically be favored to reduce orbital pressure and relieve traction on the optic nerve vasculature.     

The assistance of electronic visual aids with perceptual learning for the improvement in visual acuity in visually impaired children

International Ophthalmology - To investigate the effect of electronic visual aids (EVA) combined with perceptual learning (PL) for the improvement in visual acuity for moderate to severe visually...     

Assessing visual activities of daily living in the visually impaired

Purpose:  Visual function assessment questionnaires ask people to rate the difficulty they have performing visual activities of daily living (ADLs). This study examines the relationship between self-reported difficulty and actual performance in such ADLs.
Methods:  Twenty four subjects with established bilateral visual impairment initially self-reported their difficulty with 4 ADLs (reading newsprint, reading medicine labels, identifying coins and entering a PIN). Subjects' performance in variants of these ADLs was then assessed by measuring the time taken; by an observer rating subjects' performance; and by the subject rating their perceived difficulty with each specific task. Clinical visual function parameters were also assessed.
Results:  Varying the assessed ADL task changed how well the task correlated with self-reported difficulty. Clinical visual function, rate of task completion and observer rating of difficulty all correlated significantly with self-reported difficulty, explaining up to 69% of the variance in self-reported difficulty. However, despite replicating the ADLs as closely as possible in the clinical environment the perceived difficulty of the clinic tasks was rated as being less than the initial self-reported difficulty of the real-world task.
Conclusions:  The task variant used is important when assessing functional visual performance directly. Timed and observer-rated methods of assessment can be appropriate for assessing functional vision. In this small study, the disconnect between self-reported visual difficulty and perceived or assessed difficulty suggests that functional performance is not the only factor influencing self-report, and responses to visual function assessment questionnaires should be interpreted in this light.     

The effect of flicker rate on measured visual field extent in very young children.

PURPOSE: To investigate the effect of flicker rate on measured visual field extent in toddlers. METHODS: A total of 270 full-term children (90 each at 11-, 17-, and 30-months of age) and 36 adults were tested binocularly with an LED static perimetry procedure using a black double-arc perimeter. Each subject was tested with one of three flicker rates: 0, 3, or 10 Hz. The median farthest location seen and an interpolated estimate of the location at which 50% of the subjects detected the peripheral stimulus were calculated for each age group for each flicker rate. RESULTS: For 11-, 17-, and 30-month-old subjects, but not adults, flickering stimuli produced a larger measured visual field extent than nonflickering stimuli. For the 10-Hz stimuli, measured visual field extent in children did not differ from that of adults. CONCLUSIONS: In infants and young children, binocular measured visual field extent is enhanced by peripheral stimulus flicker. Maturity of the measured visual field depends on the stimulus parameters used during testing.     

Visual short-term effects of Viagra: double-blind study in healthy young subjects

PURPOSE: To investigate short-term visual effects of a single 100-mg dose of Viagra (sildenafil citrate) in healthy men. DESIGN: Randomized, double-blind, placebo-controlled clinical trial of drug effects on normal volunteers conducted by a single center. METHODS: Twenty men, aged 20 to 40 years, were treated with either a placebo or 100 mg sildenafil. Visual function tests included electroretinogram (ERG) recordings, on-/off- and 3.3 Hz-flicker-ERG recordings, anomaloscope matches, and measurements of cone contrast sensitivities and transient tritanopia. RESULTS: Most visual tests did not differ between the sildenafil and placebo groups. However, statistically significant increases in sensitivity during transient tritanopia were observed as well as significant prolongations in the implicit times of scotopic a-wave, photopic b-wave, and 3.3 Hz-flicker a-wave and b-wave ERG recordings. The magnitude of the differences correlated with peak sidenafil plasma concentration. Although rod amplitudes of the ERG recordings tended to be higher and cone amplitudes lower in the sildenafil group after drug ingestion, the differences were nonsignificant. There were no reports of visual side effects, and all electrophysiologic and psychophysical measurements returned to the normal range within 24 hours. CONCLUSIONS: A single oral dose of 100-mg sildenafil given to healthy young men led to small but statistically significant transient changes of outer and inner retinal function, as detected by ERG and psychophysical methods. Although the acute effects were fully reversible within 24 hours, it would be worthwhile to compare them with those induced by other PDE5 and PDE6 inhibitors.     

Study of luminance effects on pinhole test results for visually impaired patients.

PURPOSE: The visual acuity of visually impaired patients has been reported to improve after a refraction, despite pinhole test results that show a decline or no change in acuity. Our aim was to investigate whether the pinhole-induced reduction in retinal illuminance accounted for these unreliable predictions of best-corrected acuity. METHODS: Participants were 64 adult patients referred for low-vision rehabilitation. Neutral density filters reproduced the pinhole-induced luminance loss, allowing pinhole test and postrefraction acuities to be measured at essentially equivalent levels of retinal illuminance. The following data were collected in random order from each subject's better eye: (1) habitual visual acuity, (2) habitual visual acuity with filter, (3) habitual visual acuity with pinhole, (4) best-corrected/postrefraction visual acuity, (5) postrefraction visual acuity with filter. RESULTS: On average, the pinhole test under-estimated postrefraction visual acuity by six letters (95% confidence limits = +/- 20). The pinhole test underestimated postrefraction visual acuity with the filter by two letters (95% confidence limits = +/- 16). Among subjects whose acuity improved with the pinhole test (N = 24), 83% experienced better postrefraction visual acuity. Among subjects whose acuity declined or remained unchanged with the pinhole test (N = 40), 50% achieved better postrefraction visual acuity. CONCLUSIONS: The pinhole-induced luminance loss contributed to inadequate predictions of postrefraction visual acuity. Pinhole test results were enormously variable, underestimating and overestimating postrefraction visual acuity. The pinhole test was less reliable when improvements in postrefraction visual acuity were small. Visually impaired patients deserve periodic refractions, and the pinhole test result should not be used as a dichotomizer for clinical decisions regarding the need for a refraction.