Near work-induced transient myopia in Indian subjects.

PURPOSE: The aim was to determine the characteristics of near work-induced transient myopia (NITM) in asymptomatic Indian subjects and the influence of target size and contrast. METHODS: Two studies were conducted: First, 24 myopes and 24 emmetropes viewed four targets (N8 and N12 with 50 and 90 per cent contrasts) placed at 0.2 m for five minutes. The refractive status was assessed objectively, before and after carrying out the near task, with the Grand Seiko WAM-5500 open-field autorefractor under monocular viewing conditions. Second, a different group of 24 myopes and 24 emmetropes viewed a N12 target with 90 per cent contrast for 60 minutes with pre- and post-refractive state measurements repeated as above. NITM was defined as the difference between pre-task and post-task distance refraction. RESULTS: In the first study, myopes demonstrated an initial post-task myopic shift of 0.21 D, whereas emmetropes demonstrated a small hyperopic shift of 0.07 D (p < 0.001). The myopes demonstrated a decay time constant of 6.07 seconds. There was no effect of target size or contrast on the magnitude of the NITM or the decay time constant (p > 0.05). In the second study, myopes showed a NITM of 0.31 D, which was significantly greater than emmetropes (p < 0.001). The myopes demonstrated a decay time constant of 8.16 seconds. CONCLUSION: The magnitude of the NITM was higher in myopes compared to emmetropes for both five minute and 60 minute viewing time. The NITM decayed slightly faster than that found in previous literature for some other ethnic groups. Potential reasons for these findings are discussed.

Visual performance and the use of colored filters in children who are deaf.

PURPOSE: To assess visual performance and the effects of color overlays on reading in children who were deaf and children who could hear. METHODS: Thirty-one children who were deaf (mean [± SD] age, 14 [± 1.99] years) and 39 children who could hear (mean [± SD] age, 13.58 [± 3.09] years) underwent an optometric examination with specific emphasis on near vision. Participants chose an overlay with color optimal for clarity and comfort and completed the Wilkins Rate of Reading Test both with and without an overlay of this color. Nineteen of the participants who were deaf were retested a year later with a modified rate of reading test that used only words that can readily be signed. This modified rate of reading test was repeated 1 week after its first administration. RESULTS: Participants who were deaf had greater ametropia (p = 0.003), a more distant near point of convergence (p = 0.002), and reduced amplitude of accommodation (p < 0.001) compared with normal-hearing participants. All the children who were deaf chose a color overlay, with 45% choosing a yellow overlay, which increased the rate of reading by 18%. Only 66% of the participants who could hear chose an overlay, and it had no effect on reading speed. With the modified reading test, 7 of 19 (37%) again chose yellow. These participants showed a 9% increase in reading speed with the yellow overlay, which was repeatable 1 week later. The remainder showed no increase in rate of reading with their chosen overlay. CONCLUSIONS: An eye examination of children who are deaf needs to include a comprehensive assessment of near visual function so that deficiencies of amplitude of accommodation, near point convergence, and ametropia can be treated. A yellow overlay improved reading speed in the participants who were deaf, whereas other colors did not, a finding at variance with earlier work on hearing populations.

Visual performance and ocular abnormalities in deaf children and young adults: a literature review.

Visual defects are common in deaf individuals. Refractive error and ocular motor abnormalities are frequently reported, with hyperopia, myopia, astigmatism and anomalies of binocular vision, all showing a greater prevalence in deaf individuals compared with the general population. Near visual function in deaf individuals has been relatively neglected in the literature to date. Comparisons between studies are problematic due to differences in methodology and population characteristics. Any untreated visual defect has the potential to impair the development of language, with consequences for education more generally, and there is a need to improve screening and treatments of deaf children.

The Cambridge Anti-myopia Study: variables associated with myopia progression.

PURPOSE: To identify variables associated with myopia progression and to identify any interaction between accommodative function, myopia progression, age, and treatment effect in the Cambridge Anti-Myopia Study. METHODS: Contact lenses were used to improve static accommodation by altering ocular spherical aberration, and vision training was performed to improve dynamic accommodation. One hundred forty-two subjects, aged 14-21 years, were recruited who had a minimum of -0.75D of myopia. Subjects were assigned to contact lens treatment only, vision training only, contact lens treatment and vision training, or control group. Spherical aberration, lag of accommodation, accommodative convergence/accommodation (AC/A) ratio, accommodative facility, ocular biometry, and refractive error were measured at regular intervals throughout the 2-year trial. RESULTS: Ninety-five subjects completed the 24-month trial period. There was no significant difference in myopia progression between the four treatment groups at 24 months. Age, lag of accommodation, and AC/A ratio were significantly associated with myopia progression. There was a significant treatment effect at 12 months in the contact lens treatment group in younger subjects, based on a median split, aged under 16.9 years (p = 0.005). This treatment effect was not maintained over the second year of the trial. Younger subjects experienced a greater reduction in lag of accommodation with the treatment contact lens at 3 months (p = 0.03), compared to older contact lens treatment and control groups. There was no interaction between AC/A ratio and contact lens treatment effect. CONCLUSIONS: Age, lag of accommodation, and AC/A ratio were significantly associated with myopia progression. Although there was no significant treatment effect at 24 months, an interaction between age and contact lens treatment suggests younger subjects may be more amenable, at least in the short term, to alteration of the visual system using optical treatments.

A randomised clinical trial to assess the effect of a dual treatment on myopia progression: the Cambridge Anti-Myopia Study.

PURPOSE: To evaluate the effect of a dual treatment modality for myopia, by improving accommodative functions, on myopia progression. METHODS: A double blind randomised control trial was conducted on 96 subjects. The treatment modality for the trial employed custom designed contact lenses which control spherical aberration in an attempt to optimise static accommodation responses during near-work, and a vision-training programme to improve accommodation dynamics. Myopia progression was assessed over a 2 year period using cycloplegic autorefraction and biometry. RESULTS: The mean progression was found to be -0.33 Dioptres (D) over the 2 years of the study. There was no interaction between contact lens treatment and vision training treatment at 24 months (p = 0.72). There was no significant treatment effect of either Vision Training or Contact Lens Spherical Aberration control on myopia progression. CONCLUSIONS: This study is unable to demonstrate that the progression of myopia can be reduced over a 2 year period by either of the two treatments aimed at improving accommodative function. Neither treatment group (contact lens or vision training) progressed at a slower rate over the 2 years of the study than did the appropriate control group.

Peripheral refractive changes associated with myopia progression.

PURPOSE: To evaluate the changes in peripheral refraction profiles associated with myopia progression and treatment modalities used in the Cambridge Anti-Myopia Study. METHODS: one hundred and seventy-seven myopes in the age range of 14 to 22 years were enrolled in the study. The mean spherical equivalent refractive error was 3.12 1.87 diopters (D) and the refractive error of each participant was corrected with contact lenses. The participants were randomly assigned to one of four treatment groups, which included: altered spherical aberration and vision training, altered spherical aberration only, vision training only, and control. Peripheral refractive error was measured using an open field autorefractor in the central 60° of the retina in 10° steps. The refractive error was measured using cycloplegic autorefraction. Two-year refractive progression data and initial peripheral refraction measurements were available in 113 participants. Measurements of peripheral refraction and cycloplegic refraction were obtained at three visits over 2 years in 12-month intervals for 92 participants. RESULTS: All subjects showed a relative peripheral hyperopia, especially in the nasal retina. A limited magnitude of myopia progression of -0.34 ± 0.36 D over 2 years was found in each of the four groups on average. There were no significant differences in the rate of progression between any of the treatment groups (P > 0.05). Initial peripheral J45 astigmatic refractive error at 20° and 30° in the nasal retina was weakly correlated with progression of myopia over 2 years (r = -0.27, P = 0.004 and r = -0.20, P = 0.040, respectively; n = 113). The change in spherical equivalent peripheral refractive error at 30° nasal retina over time was also significantly correlated with progression of myopia especially at 24 months (r = -0.24, P = 0.017, n = 92). CONCLUSIONS: Relative peripheral hyperopia is associated with myopia. Myopia progression may be weakly linked to changes in the peripheral refraction profiles in the nasal retina. However, a causative link between peripheral refractive error and myopia progression could not be established.

The Health and Social Security Act 1984 and the price of spectacles among corporate practices in the United Kingdom (1980-2007): a review.

The Health and Social Security Act 1984 deregulated certain aspects of optometry in the United Kingdom, including advertising and the supply of spectacles, in the hope that greater competition would reduce spectacle prices. The effects of this legislation are tested by plotting the mean prices of private spectacles purchased from corporate optometric practices, from 1980 to 2007. Historical evidence is used to gauge the effect on prices of other factors such as National Health Service (NHS) payments, sight test fees and pressure exerted by consumer organisations. The high prices in 1980 reduced markedly throughout the rest of the 1980s, remained low for most of the 1990s and rose between 1999 and 2003, before falling. Changes in price were associated with changes to the system of NHS payments and variations in private sight test fees, but prices have generally been lower since the deregulation of dispensing than they were before. Although the price of private spectacles remains heavily influenced by other factors, the deregulation of opticians' services has benefited the public by maintaining lower prices, as intended by proponents of the legislation.

Linezolid-resistant ST36 methicillin-resistant Staphylococcus aureus associated with prolonged linezolid treatment in two paediatric cystic fibrosis patients.

OBJECTIVES: To describe the emergence of linezolid-resistant methicillin-resistant Staphylococcus aureus (MRSA) of sequence type (ST)36 lineage in two paediatric patients with cystic fibrosis, after long-term low-dose linezolid treatment. METHODS: Two paediatric males with cystic fibrosis had sputum samples quantitatively cultured during hospitalization. After the isolation of MRSA from both patients, oral treatment with 300 mg linezolid twice daily was initiated for periods of 1-2 months separated by up to 6 months. Isolates cultured 9 months after the start of treatment were tested for resistance to linezolid by agar dilution (BSAC). Resistant isolates were examined for 23S rDNA mutations, and typed by phage and macrorestriction with SmaI. Isolates from follow-up sputum samples were obtained until 44-51 months after treatment with linezolid. RESULTS: Colonization with MRSA was at a density of approximately 10(6) cfu/mL sputum for both subjects. Initial isolates were susceptible to linezolid, but, 9 months later, isolates from both patients were resistant (MICs > 16 mg/L). Both isolates were epidemic MRSA-16 variant A1 (ST36-MRSA-II), which is widespread in UK hospitals. Both isolates were heterozygous for a G2576T mutation in their 23S rDNA genes, but one was resistant to fusidic acid and tetracycline. In follow-up sampling, the younger patient yielded linezolid-resistant EMRSA-16 for a further 42 months, whilst the other lost the linezolid-resistant MRSA and had alternately Pseudomonas aeruginosa or linezolid-susceptible EMRSA-16 variant A1 isolated over 35 further months. CONCLUSIONS: Linezolid resistance emerged in two isolates of ST36 MRSA colonizing the lungs of two paediatric cystic fibrosis patients. Subtherapeutic levels of linezolid may have facilitated the selection of resistance.

Aberration control and vision training as an effective means of improving accommodation in individuals with myopia.

PURPOSE: To test the efficacy of a novel dual treatment for improving accommodative accuracy and dynamics in young persons with myopia. METHODS: Ninety-three young persons with myopia (mean spherical equivalent, -3.0 +/- 1.8 D; age 16.8 +/- 2.1 years; spherical aberration +0.06 +/- 0.04 microm) participated in the study. Custom-designed soft contact lenses were used to alter ocular SA to -0.10 microm to improve accommodative accuracy and reduce any lag of accommodation. A vision training regimen was performed for 18 minutes per day for up to 6 weeks to improve speed of dynamic accommodation. Control groups had contact lenses with no added SA and/or no exercises. To avoid any effects of natural levels of negative aberration on the results of the study, all participants who had negative SA were excluded. RESULTS: The treatment contact lenses produced a significant reduction in lag of accommodation (P < 0.05) at all proximal viewing distances measured. The vision training measurement and treatment resulted in a significant increase in distance facility rate for all groups compared with their own baselines (P < 0.05). Near facility rate improved in the vision training treatment group only compared with its baseline (P < 0.05). Both positive and negative response times for distant viewing were significantly shorter in all groups after training compared with their baseline values (P < 0.05). At near, the positive response times were decreased significantly (P < 0.05) in both groups, whereas the negative response times decreased significantly only in the vision training treatment group. CONCLUSIONS: After 3 months, the dual treatments (altering SA and vision training) used in the study were effective in modifying accommodation. The static accommodative response to targets at proximal distances was increased by the altered SA contact lenses and rates of dynamic accommodation improved with vision training.

Increasing negative spherical aberration with soft contact lenses improves high and low contrast visual acuity in young adults.

PURPOSE: To evaluate the effects of a customised manipulation of spherical aberration (SA) on the high and low contrast visual acuities and contrast sensitivity of young adult myopes. METHODS: A placebo-controlled double masked trial of customised spherical aberration controlling soft contact lenses was undertaken in myopes aged 15-23. Participants wore customised soft contact lenses with either (i) zero spherical aberration or (ii) negative spherical aberration that resulted in a net SA (eye plus lens) of -0.1 micron. High and low contrast log MAR visual acuities and Pelli Robson contrast sensitivity were assessed in 196 eyes of 98 subjects after a period of 12 months wearing the lenses. RESULTS: Both high and low contrast acuities were significantly better in the group wearing the contact lenses with negative spherical aberration (high contrast log MAR, p = 0.043; low contrast log MAR, p = 0.043) which was not due to differences in residual astigmatism or pupil size between the two groups. Pelli Robson contrast sensitivity was not significantly different in the two groups. CONCLUSIONS: Manipulation of spherical aberration, taking account of the participants' baseline level of aberration, can cause statistically significant improvements in high and low contrast distance visual acuity although these improvements are too small in magnitude to be of clinical significance.

The effect of altering spherical aberration on the static accommodative response.

PURPOSE: To investigate the effect of altering the spherical aberration (SA) of the eye on the static accommodative response. METHODS: Participants were fitted with nominally afocal contact lenses with controlled amounts of SA of either -0.2, -0.1, 0.0, +0.1 or +0.2 microm for a 5-mm pupil. Measurements of SA and root mean square (RMS) total aberration for the eye plus lens for each participant were determined with a Complete Ophthalmic Analysis System aberrometer. Accommodation was stimulated either by placing targets at different dioptric distances from the eye, or by using a fixed distance target and placing negative-powered lenses in front of the eye. Accommodation responses were determined with a Shin-Nippon autorefractor. RESULTS: For both stimuli situations, the slope of the accommodation stimulus-response function was lowest for the lenses with +0.2 microm SA, and increased as the amount of SA was reduced. There was a significant negative correlation between SA and slope. Lag of accommodation at 33 cm correlated well with added SA, but did not correlate with total RMS error. There was no significant difference between the responses at 30 min after lens wear started and the responses after 1 h. CONCLUSIONS: Adding negative SA to the eye generally improves the slope of the accommodation stimulus-response curve and decreases lag of accommodation, and positive added SA depresses the slope of the stimulus-response curve and increases lag. The effect seems to be specific to SA, as there was no relationship between lag and RMS error. Altering SA may be a viable way of changing accommodative functions in clinical situations.

Peripheral refraction for distance and near vision in emmetropes and myopes.

We investigated the relationship between myopia and peripheral refraction for distance and near vision by measuring peripheral refractive errors in 10 myopic and 10 emmetropic participants at viewing distances of 2.5 and 0.4 m. Measurements were made at the fovea, and at eccentricities of 10 degrees , 20 degrees and 30 degrees in the temporal and nasal hemispheres of the horizontal visual field. Our results showed that peripheral astigmatism increased with increasing eccentricity, but there was no significant difference between refractive error groups except at 30 degrees eccentricity in the temporal retina. Considering the Mean Spherical Equivalent errors, emmetropes became relatively myopic at peripheral eccentricities, but there was little change in myopes. The effect of viewing distance on astigmatism or Mean Spherical Equivalent error was not significant. Our results do not support the view that myopia is associated with changes in peripheral refraction during distance or near vision.

Effect of positive and negative defocus on contrast sensitivity in myopes and non-myopes.

This study investigated the effect of lens induced defocus on the contrast sensitivity function in myopes and non-myopes. Contrast sensitivity for up to 20 spatial frequencies ranging from 1 to 20 c/deg was measured with vertical sine wave gratings under cycloplegia at different levels of positive and negative defocus in myopes and non-myopes. In non-myopes the reduction in contrast sensitivity increased in a systematic fashion as the amount of defocus increased. This reduction was similar for positive and negative lenses of the same power (p = 0.474). Myopes showed a contrast sensitivity loss that was significantly greater with positive defocus compared to negative defocus (p = 0.001). The magnitude of the contrast sensitivity loss was also dependent on the spatial frequency tested for both positive and negative defocus. There was significantly greater contrast sensitivity loss in non-myopes than in myopes at low-medium spatial frequencies (1-8 c/deg) with negative defocus. Latent accommodation was ruled out as a contributor to this difference in myopes and non-myopes. In another experiment, ocular aberrations were measured under cycloplegia using a Shack-Hartmann aberrometer. Modulation transfer functions were calculated using the second order term for defocus as well as the fourth order Zernike term for spherical aberration. The theoretical maximal contrast sensitivity based on aberration data predicted the measured asymmetry in contrast sensitivity to positive and negative defocus that was observed in myopic subjects. The observed asymmetry in contrast sensitivity with positive and negative defocus in myopes may be linked to the altered accommodative response observed in this group.

Crowding under scotopic conditions.

Under certain circumstances, a subject's ability to discriminate spatial features of a target may be hampered by neighbouring contours. This phenomenon is popularly known as the "crowding effect", and it has been intensely studied for photopic vision: little attention has been paid to the effect at lower light levels. The underlying basis of the crowding effect has recently provoked some conjecture, with Hess and colleagues claiming that a passive "physical" phenomenon may either wholly [Vis. Res. 40 (2000) 365], or partially [J. Opt. Soc. Am. A--Opt. Image Sci. Vis. 17 (2000) 1516], account for the effect. In order to investigate the crowding effect under scotopic conditions, we conducted scotopic frequency of seeing experiments for Landolt C targets presented both with, and without, flanking bars; the size of the targets was varied so that frequency of seeing curves could be derived for each stimulus condition. Our results suggest that the spatial extent of crowding is significantly less for scotopic vision than for photopic vision at the same eccentricity--furthermore the effect does not seem to scale in proportion to target size. We also compared the resulting empirical curves to those that would be predicted by the hypothesis of Hess and colleagues. Our results do not support the hypothesis that the scotopic crowding effect is caused by a passive physical process.

Unequal reduction in visual acuity with positive and negative defocusing lenses in myopes.

Myopes have a reduced accommodative response to negative lenses compared with nonmyopes. Mathematical models predict that the reduced accommodative response is due to a decrease in sensitivity to blur in myopes. We examined the effect of blur induced by positive and negative defocusing lenses on visual acuity in 12 myopes and 12 nonmyopes during cycloplegia for up to +/-3.00 D of defocus in 0.25 D steps. Although nonmyopes showed a symmetrical reduction in visual acuity with positive and negative lenses, the myopic group showed less acuity loss with negative lenses compared with positive lenses. The magnitude of visual acuity loss was lower with negative lenses in myopes compared with nonmyopes. No significant difference in visual acuity with positive lenses was found between myopes and nonmyopes. Residual accommodation (after cycloplegia) was about 0.20 D in both myopes and nonmyopes and was too small to explain the relatively good visual acuity through minus lenses in the myopic group. The reduced accommodative response known to occur in myopes may be due to the relatively small effect that negative lens blur has on their visual acuity.