Senile macular degeneration: a case-control study

Senile macular degeneration, although a leading cause of visual loss in the United States, remains a poorly understood disease. To assess the effects of host and environmental factors on this condition, a study of 228 cases and 237 controls matched by age and sex, who had visited any of 34 Baltimore ophthalmologists between September 1, 1978 and March 31, 1980, was conducted. Study participants were interviewed for past medical, residential, occupational, smoking and family histories, as well as social and demographic factors. Diagnoses were validated by means of fundus photographs. The 162 cases and 175 controls who met the study diagnostic criteria for cases and controls were included in the analysis. Statistically significant associations were demonstrated between senile macular degeneration and family history of macular disease (odds ratio (OR) = 2.9), chemical work exposures (OR = 4.2), blue or medium pigmented eyes (OR = 3.5), history of one or more cardiovascular diseases (OR = 1.7), decreased hand grip strength, and hyperopia. The risk of macular degeneration in cigarette smokers was significant for males only (OR = 2.6). The study results suggest that the development of macular degeneration is mainly influenced by familial, genetic, and personal characteristics, rather than by the few environmental factors studied. Additional studies are needed to further evaluate the role of environmental factors.

Amblyopia

Results from recent randomised clinical trials in amblyopia should change our approach to screening for and treatment of amblyopia. Based on the current evidence, if one screening session is used, screening at school entry could be the most reasonable time. Clinicians should preferably use age-appropriate LogMAR acuity tests, and treatment should only be considered for children who are clearly not in the typical range for their age. Any substantial refractive error should be corrected before further treatment is considered and the child should be followed in spectacles until no further improvement is recorded, which can take up to 6 months. Parents and carers should then be offered an informed choice between patching and atropine drops. Successful patching regimens can last as little as 1 h or 2 h a day, and successful atropine regimens as little as one drop twice a week. Intense and extended regimens might not be needed in initial therapy.

Peripheral refraction along the horizontal and vertical visual fields in myopia

Peripheral refractions were measured to 35 degrees eccentricity using a free-space autorefractor in young adult emmetropic and myopic subjects. Refractions were measured along horizontal and vertical visual fields for 116 subjects and a 43 subject subset, respectively. Along the horizontal visual field, peripheral myopic shifts in spherical equivalent M of emmetropes changed to relative hypermetropic shifts in the myopes, there were temporal-nasal asymmetries of 90 degrees to 180 degrees astigmatism J(180) which decreased as myopia increased, and 45 degrees to 135 degrees astigmatism J(45) was linearly related to field angle. Along the vertical visual field, both peripheral myopic shifts in peripheral M and J(180) asymmetry were unaffected by magnitude of myopia, and J(45) changed at three times the rate as for the horizontal visual field. Myopia has more effect on peripheral refraction of adult eyes along the horizontal than along the vertical visual field. The peripheral variations in refraction match well what is known about the shapes of emmetropic and myopic eyes.

Retinoic acid signals the direction of ocular elongation in the guinea pig eye

A growing eye becomes myopic after form deprivation (FD) or compensates for the power and sign of imposed spectacle lenses. A possible mediator of the underlying growth changes is all-trans retinoic acid (RA). Eye elongation and refractive error (RE) was manipulated by raising guinea pigs with FD, or a spectacle lens worn on one eye. We found retinal-RA increased in myopic eyes with accelerated elongation and was lower in eyes with inhibited elongation. RA levels in the choroid/sclera combined mirrored these directional changes. Feeding RA (25 mg/kg) repeatedly to guinea pigs, also resulted in rapid eye elongation (up to 5 times normal), and yet the RE was not effected. In conclusion, RA may act as a signal for the direction of ocular growth.

Improving vision: neural compensation for optical defocus

Anecdotal reports abound of vision improving in myopia after a period of time without refractive correction. We explored whether this effect is due to an increased tolerance of blur or whether it reflects a genuine improvement in vision. Our results clearly demonstrated a marked improvement in the ability to detect and recognize letters following prolonged exposure to optical defocus. We ensured that ophthalmic change did not occur, and thus the phenomenon must be due to a neural compensation for the defocus condition. A second set of experiments measured contrast sensitivity and found a decrease in sensitivity to mid-range (5-25 cycles deg-1) spatial frequencies following exposure to optical defocus. The results of the two experiments may be explained by the unmasking of low contrast, high spatial frequency information via a two-stage process: (1) the pattern of relative channel outputs is maintained during optical defocus by the depression of mid-range spatial frequency channels; (2) channel outputs are pooled prior to the production of the final percept. The second set of experiments also provided some evidence of inter-ocular transfer, indicating that the adaptation process is occurring at binocular sites in the cortex.

Incidence and progression of myopia and associated factors in urban school children in Delhi: The North India Myopia Study (NIM Study)

Aim

To evaluate the incidence and progression of myopia and factors associated with progression of myopia in school going children in Delhi.

Methods

Prospective longitudinal study of 10,000 school children aged 5 to 15 years screened after an interval of 1 year to identify new myopes (Spherical Equivalent≤ -0.5D) and progression of myopia in previously diagnosed myopic children. Association between risk factors and progression was analyzed using adjusted odds ratio.

Results

Of the 9,616 children re-screened (97.3% coverage), annual incidence of myopia was 3.4%with mean dioptric change of -1.09 ± 0.55. There was a significant higher incidence of myopia in younger children compared to older children (P = 0.012) and among girls compared to boys (P = 0.002). Progression was observed in 49.2%children with mean dioptric change of -0.27 ± 0.42 diopters. The demographic and behavioral risk factors were analyzed for children with progression (n = 629) and adjusted odds ratio values were estimated. Hours of reading-writing/week (p<0.001), use of computers/ video games (P<0.001) and watching television (P = 0.048) were significant risk factors for progression of myopia. Outdoor activities / time spent outdoors> 2 hours in a day were protective with an inverse association with progression of myopia (P< 0.001).

Conclusion

Myopia is an important health issue in India and is associated with long hours of reading and screen time with use of computers and video games. An annual eye vision screening should be conducted, and outdoor activities be promoted to prevent the increase of myopia among school children.

Causes of visual impairment in people aged 75 years and older in Britain: an add-on study to the MRC Trial of Assessment and Management of Older People in the Community

BACKGROUND

Visual impairment and blindness are common in older people in Britain. It is important to know the causes of visual impairment to develop health service and research priorities. The authors aimed to identify the causes of visual impairment in people aged 75 years and older in Britain.

METHODS

In the MRC Trial of the Assessment and Management of Older People in the Community, trial nurses tested visual acuity in everyone aged 75 years and older in 53 general practices. For all visually impaired patients in 49 of the 53 medical practices, data regarding the cause of vision loss were extracted from the general practice medical notes. Additional follow up questionnaires were also sent to the hospital ophthalmologist to confirm the cause of vision loss. Visual impairment was defined as a binocular acuity of less than 6/18.

RESULTS

There were 1742 (12.5%) people visually impaired in the 49 participating practices. Of these, 450 (26%) achieved a pinhole visual acuity in either eye of 6/18 or better. In these people, the principal reason for visual loss was considered to be refractive error. The cause of visual loss was available for 976 (76%) of the remaining 1292 visually impaired people identified. The main cause of visual loss was age related macular degeneration (AMD); 52.9% (95% confidence interval 49.2 to 56.5) of people had AMD as a main or contributory cause. This was followed by cataract (35.9%), glaucoma (11.6%), myopic degeneration (4.2%), and diabetic eye disease (3.4%).

CONCLUSIONS

A substantial proportion of visual impairment in our sample of older people in Britain can be attributed to remediable causes-refractive error and cataract. There is considerable potential for visual rehabilitation in this age group. For the large proportion with macular degeneration, low vision services will be important.

Classification of congenital and early onset retinitis pigmentosa

We retrospectively studied 36 patients with congenital (Leber's amaurosis) and early onset retinitis pigmentosa (RP) to develop a new schematic classification system based on the age at onset of symptoms, severity of visual loss, and associated nonocular abnormalities. Our four groups were designated as complicated and uncomplicated Leber's congenital amaurosis and juvenile and early onset RP. Criteria for patient selection included an extinguished or barely recordable electroretinogram, well-documented age of onset, and comprehensive ocular and medical examinations before the age of 10 years. Among the congenitally blind, the distinguishing features were the degree of hyperopia and the presence or absence of neurologic abnormalities. Among patients with infantile or juvenile onset of retinal degeneration, the distinguishing features were the severity of visual loss and the age at onset of symptoms. The presence of nystagmus and hyperopia and the severity of central visual loss differentiated congenital from early onset RP.

Normal ocular development in young rhesus monkeys (Macaca mulatta)

PURPOSE

The purpose of this study was to characterize normal ocular development in infant monkeys and to establish both qualitative and quantitative relationships between human and monkey refractive development.

METHODS

The subjects were 214 normal rhesus monkeys. Cross-sectional data were obtained from 204 monkeys at about 3 weeks of age and longitudinal data were obtained from 10 representative animals beginning at about 3 weeks of age for a period of up to 5 years. Ocular development was characterized via refractive status, corneal power, crystalline lens parameters, and the eye's axial dimensions, which were determined by retinoscopy, keratometry, phakometry and A-scan ultrasonography, respectively.

RESULTS

From birth to about 5 years of age, the growth curves for refractive error and most ocular components (excluding lens thickness and equivalent lens index) followed exponential trajectories and were highly coordinated between the two eyes. However, overall ocular growth was not a simple process of increasing the scale of each ocular component in a proportional manner. Instead the rates and relative amounts of change varied within and between ocular structures.

CONCLUSION

The configuration and contribution of the major ocular components in infant and adolescent monkey eyes are qualitatively and quantitatively very comparable to those in human eyes and their development proceeds in a similar manner in both species. As a consequence, in both species the adolescent eye is not simply a scaled version of the infant eye.

The Refractive Status and Vision Profile: Evaluation of psychometric properties and comparison of Rasch and summated Likert-scaling

The psychometric properties of the Refractive Status and Vision Profile (RSVP) questionnaire were evaluated using Rasch analysis. Ninety-one myopic patients from a refractive surgery clinic and general optometric practice completed the RSVP. Rasch analysis of the RSVP ordinal data was performed to examine for unidimensionality and item reduction. The traditional Likert-scoring system was compared with a Rasch-scored RSVP and a reduced item Rasch-scored RSVP. Rasch analysis of the original RSVP showed poor targeting of item difficulty to patient quality of life, items with a ceiling effect and underutilized response categories. Combining the underutilized response scales and removal of redundant and misfitting items improved the internal consistency and targeting of the RSVP, and the reduced 20-item Rasch scored RSVP showed greater relative precision over standard Likert scoring in discriminating between the two subject groups. A Rasch scaled quality of life questionnaire is recommended for use in refractive outcomes research.

Environmental Factors and Myopia: Paradoxes and Prospects for Prevention

The prevalence of myopia in developed countries in East and Southeast Asia has increased to more than 80% in children completing schooling, whereas that of high myopia has increased to 10%-20%. This poses significant challenges for correction of refractive errors and the management of pathological high myopia. Prevention is therefore an important priority. Myopia is etiologically heterogeneous, with a low level of myopia of clearly genetic origins that appears without exposure to risk factors. The big increases have occurred in school myopia, driven by increasing educational pressures in combination with limited amounts of time spent outdoors. The rise in prevalence of high myopia has an unusual pattern of development, with increases in prevalence first appearing at approximately age 11. This pattern suggests that the increasing prevalence of high myopia is because of progression of myopia in children who became myopic at approximately age 6 or 7 because age-specific progression rates typical of East Asia will take these children to the threshold for high myopia in 5 to 6 years. This high myopia seems to be acquired, having an association with educational parameters, whereas high myopia in previous generations tended to be genetic in origin. Increased time outdoors can counter the effects of increased nearwork and reduce the impact of parental myopia, reducing the onset of myopia, and this approach has been validated in 3 randomized controlled trials. Other proposed risk factors need further work to demonstrate that they are independent and can be modified to reduce the onset of myopia.

Near vision, lags of accommodation and myopia

It is shown that, with some simplifying assumptions about the nature of the accommodation response/stimulus curve, geometrical optics predicts that lags in accommodation will result in ocular modulation transfer for any linear size of grating component in an object being independent of object distance. Thus bringing an object nearer to the eye should not improve the contrast of the retinal image of any of its details. However, when the effects of diffraction and aberration are considered, together with the angular spatial frequency dependence of the retinal contrast threshold, the expected advantages of short observation distances for the detection of fine detail emerge. It is shown that a reduced slope for the accommodation response/stimulus curve leads to increased lag and reduced modulation transfer: the possible role of such effects in the development of some types of myopia is discussed.

Risk factors of branch retinal vein occlusion

A case-control study of 225 patients with branch retinal vein occlusion (BRVO) and 100 age-matched controls was conducted to assess potential clinical risk factors for BRVO. Male gender, hypertension, and hyperopia were significantly more prevalent in patients with BRVO. There was no significant association with race, diabetes, or chronic open-angle glaucoma.

Effects of Optically Imposed Astigmatism on Emmetropization in Infant Monkeys

PURPOSE

Although astigmatism is prevalent during early infancy, the influence of astigmatism on early refractive development is unclear. This study was undertaken to determine the effects of astigmatism on emmetropization in monkeys.

METHODS

Infant rhesus monkeys (n = 39) were exposed to optically simulated astigmatism in one or both eyes from approximately 1 to 4 months of age. With-the-rule, against-the-rule, and oblique astigmatisms were optically simulated by appropriately orienting the principal meridians of the spherocylindrical treatment lenses (+1.50 -3.00 D x 90 degrees, 180 degrees, 45 degrees, or 135 degrees; i.e., +1.50 and -1.50 D powers in the two principal meridians). Refractive development was assessed every 2 to 3 weeks by cycloplegic retinoscopy, keratometry and corneal videotopography, and A-scan ultrasonography. Data from 19 control monkeys, including 3 animals that were reared with binocular plano lenses, were used for comparison purposes.

RESULTS

Most of the cylinder-lens-reared monkeys, regardless of the orientation of the imposed astigmatism, showed clear signs of either hyperopic or myopic growth compared with control monkeys. The distributions of refractive error and vitreous chamber depth both showed bimodal patterns that differed from normal by amounts equivalent to the optical powers of the principal meridians of the treatment lenses. More frequently, refractive development was biased toward the eye's least-hyperopic focal plane. The refractive changes were mainly axial. After lens removal, the lens-reared monkeys recovered and as a group exhibited refractive errors and axial dimensions similar to those in control monkeys.

CONCLUSIONS

In the presence of significant amounts of astigmatism, emmetropization is directed toward one of the two focal planes associated with the astigmatic principal meridians and not the circle of least confusion. These results suggest that the mechanisms responsible for emmetropization are insensitive to stimulus orientation and the global form of the retinal image. It appears that emmetropization seeks out the image plane that contains the maximum effective contrast integrated across spatial frequency and stimulus orientation.

Visual acuity and accommodation in infants and young children with Down's syndrome

Accommodation and visual acuity were measured in 53 children with Down's syndrome aged between 12 weeks and 57 months. Results were compared with data for 136 control (typically developing) children aged between 4 weeks and 48 months. Whereas the control children accommodated accurately on near targets, accommodation was defective in 92% of the children with Down's syndrome, and there was no change in accommodative ability with age. On the other hand, visual acuity lay within normal limits for the younger children. Children over the age of 2 years showed a below-normal visual acuity, which is not explained either by refractive error or by the effect of poor accommodation. The data suggest a sudden change in the rate of development of visual acuity which may be associated with physiological changes in the visual cortex. Previously reported defects of accommodation and visual acuity in older children and adults with Down's syndrome are confirmed by our findings in infants and young children.

Neural and optical limits to visual performance in myopia

We investigated the relative importance of neural and optical limitations to visual performance in myopia. A number of visual performance measures were made on all or subsets of 121 eyes of emmetropic and myopic volunteers aged 17-35 years. These tests included visual measures that are mainly neurally limited (spatial summation out to +/-30 degrees in the horizontal visual field and resolution acuity out to +/-10 degrees in the horizontal visual field) and central ocular aberrations. We found that myopia affected the neurally limited tests, but had little effect on central higher order aberration. The critical area for spatial summation increased in the temporal visual field at 0.03 log units/dioptre of myopia. Resolution acuity decreased at approximately 0.012 log units/dioptre of myopia. Losses of visual function were slightly greater in the temporal than in the nasal visual field. The observed visual deficit in myopia can be explained by either global retinal expansion with some post-receptor loss (e.g. ganglion cell death) or a posterior polar expansion in which the point about which expansion occurs is near the centre of the previously emmetropic globe.

The normal cup-disk ratio

We determined the cup-disk ratios of 580 individuals, ranging in age from 4 to 91 years, with a Hruby lens; we also determined the cup-disk ratios of 289 of the 580 with a direct ophthalmoscope. All had applanation pressures of 18 mm Hg or less. There was no linear relationship (covariation) between cup-disk ratio and refractive error or intraocular pressure, but there was a tendency toward increasing cup-disk ratio with increasing age. The mean cup-disk ratio in the group examined with the Hruby lens was 0.38 and that in the group examined with the direct ophthalmoscope was 0.25. With either method almost all eyes had cup-disk ratios of 0.7 or less. In 9% of the eyes the cup was ovoid. In only 10% of these cases was the vertical cup-disk ratio greater than the horizontal cup-disk ratio, and in only one case was this difference 0.2 or more. The Hruby lens method consistently gave a slightly larger cup-disk ratio than the direct ophthalmoscope did. However, there was seldom a disparity of more than 0.2. The Hruby lens or biomicroscopic lens should be used to determine the fullest extent of the contour of the cup. Any cup-disk ratio of 0.7 or more, any vertical cup-disk ratio larger than the horizontal cup-disk ratio, and any disparity between the direct ophthalmoscope estimation and Hruby lens estimation of more than 0.2 should be viewed with suspicion.