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.

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.

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.

Distance word acuity, critical print size and driving vision standards.

BACKGROUND: A comparison was made between letter visual acuity and word acuity at distance and between letter acuity and the minimum word size allowing maximum and fluent reading speeds. METHODS: Visual acuities were measured at six metres for 120 participants. Letter acuity was assessed with a logMAR layout chart with Sloan letters displayed with Thomson XPert software. A logMAR layout lowercase word chart was created in PowerPoint using the format of the MNRead near chart, with the font and colours found on United Kingdom motorway signs. Distance letter and word acuity, maximum reading speed, critical print size (CPS) and minimum print size for fluent reading were calculated. RESULTS: Word and letter acuities were significantly correlated (p < 0.001) and showed a statistically (p = 0.049) but not clinically significant mean difference of 0.02 ± 0.09 logMAR. Bland-Altman analysis showed that agreement between charts varied depending on acuity level with word acuity better than letter acuity at levels closer to the driving standard of +0.30 logMAR (6/12). Maximum reading speed was achieved from print sizes 1.5 logMAR lines larger than the letter acuity and fluent reading at 80 words per minute from print sizes 0.06 logMAR larger than the letter acuity. CONCLUSION: These results allow equivalent lowercase print sizes supporting either functional reading or maximum reading speeds to be calculated based on letter chart acuities at distance. Minimum print sizes allowing either functional or maximum reading speeds are more appropriate than threshold word acuities, where groups of words or short phrases need to be identified, such as when driving. Where a driving vision standard of +0.30 logMAR (6/12) exists, a person just meeting the driving standard should be able to read fluently words on signage in lowercase x-heights equivalent to between +0.29 and +0.30 logMAR.

Advising patients on visual fitness to drive: implications of revised DVLA regulations.

AIM: To examine the relationship between the two UK vision standards for driving: the ability to read a number-plate at 20 m and achieving 6/12 (+0.30 logMAR). METHODS: 120 participants were assessed without refractive correction in this cross-sectional study. Vision was assessed with a Snellen chart, Early Treatment of Diabetic Retinopathy Study (ETDRS) style logMAR letter chart and logMAR chart using Landolt rings. Ability to read a post-2001 number-plate was assessed outdoors. RESULTS: For all charts, there was an 'overlap zone' of visions within which it was uncertain whether participants would pass the number-plate test. Within this zone, sensitivity and specificity of the 6/12 cut-off for predicting number-plate performance were reasonable for Snellen and ETDRS style charts, but poor for Landolt. All participants with 6/7.5 Snellen (+0.10 logMAR ETDRS) or better could read a number-plate. Some participants (2-6%) with vision between this level and 6/12 could not read a number-plate, and 14%-15% could read a number-plate but not achieve 6/12. CONCLUSIONS: To best predict drivers' ability to read a number-plate, vision should be assessed using a logMAR letter chart or a Snellen chart scored by full line. Drivers with 6/7.5 (+0.10 logMAR) or better vision can be advised that they meet the driving standard. Drivers with acuity between 6/9 and 6/12 (+0.12-+0.30 logMAR) should be advised to check their ability to read a number-plate, as some may not be able to. Clinicians will see patients who can read a number-plate, but do not achieve 6/12, who will need improved vision to meet visual requirements for driving.

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 effect of soft contact lens wear and time from blink on wavefront aberration measurement variation.

INTRODUCTION: Advances in contact lens design technology allow incorporation of correction of higher-order aberrations to improve or manipulate the eye's optical quality. Repeatability of aberration measurements in vivo with contact lens wear has not been established. METHOD: Higher-order aberrations were measured using the COAS aberrometer (Wavefront Sciences, USA) in 23 participants who were free from external eye pathology. Cycloplegia with 1% Cyclopentolate HCl ensured control of accommodation and that pupil diameters exceeded analysis diameter. Tear film characteristics were assessed with the phenol red thread test and Keeler Tearscope. Variability in wavefront aberrations was assessed with and without a low powered soft contact lens. The effect of time after the blink and tear film characteristics were also investigated. RESULTS: Standard deviations differed significantly for some fifth-order terms (p < or = 0.003) with contact lens wear. Coefficient of variation did not increase significantly with contact lens wear. Time from blink increased standard deviations in the third-order (p < or = 0.003). The effect of contact lens wear and time from blink differed between groups with different tear film characteristics. CONCLUSIONS: Variability in measurements of aberrations increased significantly for odd-order aberrations when a contact lens was worn or between blinks. Fourth-order aberrations showed less effect of contact lens wear. Therefore, verification of the performance of lenses with aspheric optics on eye is feasible. Accurate assessment of higher-order aberrations is more difficult when a contact lens is worn. Both contact lens wear and time from blink increase variability in aberrations, which suggests a role for the tear film in increased aberrations with soft contact lens wear.

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.