The effects of spectacle wear in infancy on eye growth and refractive error in the marmoset (Callithrix jacchus).

We made a comprehensive study, involving observations on 45 marmosets, of the effects on ocular growth and refraction of wearing spectacles from the ages of 4-8 weeks. This period was within the period early in life when the eye grows rapidly and refraction changes from hyperopia to its adult value of modest myopia. In one series of experiments we studied the effect of lenses of powers -8, -4, +4 and +8D fitted monocularly. In another series of experiments we studied the effect of lenses of equal and opposite powers fitted binocularly, with the two eyes alternately occluded, so as to give an incentive to use both eyes, and in particular to accommodate, for at least part of each day, through the negative lens. The vitreous chamber of eyes that wore negative lenses of -4D or -8D, combined with alternate occlusion, elongated more rapidly than that of the fellow eye (negative lens eye-positive lens eye, 0.21 +/- 0.03 mm (S.E.M.), P < 0.01 and 0.25 +/- 0.06 mm, P < 0.05, respectively) and became relatively more myopic (2.8 +/- 0.26D, P < 0.01 and 2.4 +/- 0.61D, P < 0.05 respectively). Eyes that wore -4D lenses monocularly elongated more rapidly and became myopic than fellow eyes. Eyes that wore +4D or +8D lenses were less strongly affected: animals that wore +8D lenses monocularly (without alternate occlusion) developed a slight relative hyperopia (0.99 +/- 0.21D, P < 0.01), with the more hyperopic eyes also slightly shorter (0.09 +/- 0.05 mm) than their fellow eyes, but eyes wearing +4D lenses were not significantly different from their fellow eyes. Animals that wore -8D lenses monocularly (without alternate occlusion) developed a slight relative hyperopia after three weeks of lens-wear (0.85 +/- 0.26D, P < 0.05). These were the only eyes that responded in a non-compensatory direction to the optical challenge of spectacle wear, and we interpret this effect as one due to visual deprivation. After the removal of lenses, the degree of anisometropia slowly diminished in those groups of animals in which it had been induced, but in the three groups in which the largest effects had been produced by lens-wear the overall mean anisometropia (0.68 +/- 0.24D, P < 0.01) and vitreous chamber depth (VCD) discrepancy (0.09 +/- 0.03 mm, P < 0.01) were still significant at the end of the experiments, when the animals were 273 days old. The reduction of anisometropia in these groups was associated with an increase in the rate of elongation of the vitreous chamber in the eyes that had previously grown normally i.e. the less myopic eyes grew more rapidly than their fellow eyes: in the seven weeks following lens-wear these eyes became more myopic and longer than normal eyes (refraction P < 0.001; VCD P < 0.001). Control experiments showed that occlusion of one eye for 50% of the day had no effect on eye growth and refraction, and therefore that alternate occlusion itself had no effect.     

屈光性调节性内斜视儿童戴镜后的屈光演变

目的探讨屈光性调节性内斜视儿童戴镜后屈光状态随年龄的变化规律,为临床随访时间及配镜提供依据。方法回顾我院65例（130眼）屈光性调节性内斜视儿童连续多年的屈光数据,对主导眼和非主导眼的屈光度比较采用配对t检验,对屈光度差值与观察期进行直线回归分析。结果等效球镜度、球镜度、散光度差值与月龄存在直线回归关系（P〈0．01）。主导眼和非主导眼等效球镜度月平均分别减少0．015 D和0．012 D;等效球镜度改变规律为远视度先增加后减少,而后有逐渐向近视方向发展的趋势;转变年龄为3．58～4．90岁;散光度月平均演变速度仅为0．002 D。结论屈光性调节性内斜视儿童戴镜后屈光状态随着年龄的增长,远视度先增加后减少,而后有逐渐正视化趋势：年均改变速度〈0．25 D。     

A population-based survey of the prevalence of refractive error in Malawi

Refractive errors, particularly myopia, are a common problem in industrialized countries, but the impression exists that myopia may be relatively uncommon in non-industrialized societies.

We conducted a population-based survey of refractive error in two groups of Malawians: a group of rural agricultural workers (n = 510) and a group of students at an urban teachers' college (n = 534).

The overall prevalence of myopia was low; 2.5% (95% confidence interval 1.3%, 3.7%) of participants had an error of-0.5 D or greater. The mean refractive error (right eye) in the urban student group was +0.52 D compared to +0.62 D among the rural agricultural workers and the excess myopia was accounted for by significant myopia (≥-0.75 D) in a few individuals, rather than an overall shift towards myopia within the urban student group. Among the rural agricultural workers, literacy predicted refractive error (right eye), with a mean of +0.59 D in the rural literate compared to +0.67 D in the rural illiterate.

These findings support the notion that myopia is uncommon in non-industrialized societies and that it is associated with increased literacy but we have not identified specific risk factors within this group to predict the occurrence of significant myopia. In settings such as Malawi, refractive services should be targeted to urban centers, where more educated populations are likely to be found.     

停戴角膜塑形镜后屈光度及角膜屈光力回退的临床观察

目的观察短期停戴角膜塑形镜后屈光度及角膜屈光力回退率。方法自身对照研究。36例（69眼）患者配戴角膜塑形镜3个月效果稳定,复查时在摘镜后即时、摘镜10h、摘镜24h观察停戴镜片后的改变。观察指标包括裸眼视力、主观验光、角膜地形图检查。根据已被矫正的屈光度分为3组：〉-4.50D组,-3.12--4.50 D组,-0.12--3.00D组。采用描述性统计方法。结果摘镜后不同时间点各参数均逐渐回退。摘镜10h及摘镜24h,裸眼视力（10gMAR）分别回退0.09-0.20（回退率为11％）和0.30±0.24（回退率为36％）。等效球镜度分别回退（0.25±0.74）D（回退率为8％）和（1.15±1.05）D（回退率为36％）,角膜平均屈光力（simK）分别回退（0.00±0.85）D（回退率0％）和（0.62±0.68）D（回退率为46％）。不同组别回退速度不同,配戴前屈光度越高,停戴后回退的速度越快。结论摘镜后白天10h屈光度及角膜屈光力可保持相对稳定,停戴24h后回退明显,且配戴前屈光度越高,回退的速度越快。     

Prevalence and predictors of refractive error and spectacle coverage in Nakuru, Kenya: a cross-sectional, population-based study

A cross-sectional study was undertaken in Nakuru, Kenya to assess the prevalence of refractive error and the spectacle coverage in a population aged ≥50 years. Of the 5,010 subjects who were eligible, 4,414 underwent examination (response rate 88.1 %). LogMAR visual acuity was assessed in all participants and refractive error was measured in both eyes using a Topcon auto refractor RM8800. Detailed interviews were undertaken and ownership of spectacles was assessed. Refractive error was responsible for 51.7 % of overall visual impairment (VI), 85.3 % (n = 191) of subjects with mild VI, 42.7 % (n = 152) of subjects with moderate VI, 16.7 % (n = 3) of subjects with severe VI and no cases of blindness. Myopia was more common than hyperopia affecting 59.5 % of those with refractive error compared to 27.4 % for hyperopia. High myopia (<?5.0 DS) was also more common than extreme hyperopia (>+5.0 DS). Of those who needed distance spectacles (spectacle coverage), 25.5 % owned spectacles. In conclusion, the oldest, most poor and least educated are most likely to have no spectacles and they should be specifically targeted when refractive services are put in place.     

Variations of refractive error during the first year of contact lens wear

The variations of refractive errors during both hard, hydrophilic and silicone lens wear were significantly correlated in the 2 eyes of each individual. In each lens group the mean changes of spherical and cylindrical refractive errors were small (-0.458D-+0.250D and -0.325D-+0.056D, respectively). Considerable individual refractive changes occurred (spherical change: -3.0D-+1.5D, cylindrical change: -2.5D-+1.0D). However, only 2 subjects noticed spectacle blur and a normal visual acuity was always obtained by spectacle refraction immediately after lens removal. This indicated that clinically significant distortion of the central cornea did not take place. Hydrophilic lens wearers showed an increasing myopia during lens wear. Otherwise the refractive changes were not significantly influenced by the duration of lens wear. Refractive changes appeared to be significantly correlated to changes of the central anterior corneal curvature, the ratio of dioptric changes being about 1:1.     

Aphakia: perceptual and refractive problems of spectacle correction

The perceptual variations due to removal of the crystalline lens and the employment of powerful plus spectacle lenses are described. These include refractive change, distortion, magnification, limitation of the visual field, peripheral vision, sensitivity of light and changes in the required convergence. The technique for satisfactory refraction of the aphakic eye is discussed and the elements leading to error such as vertex distance and pantoscopic tilt are considered. Other factors necessary for understanding the refraction such as the apparent accommodative range and the limitations affecting field charting are also covered. Method of securing binocularity via contact lens-spectacle combinations for monocular cases, and the need for rehabilitative procedures conclude this treatment.     

Ultraviolet light, cataracts, and spectacle wear

Two groups of patients older than 60 years were examined for degree of development of nuclear sclerotic cataracts. The first group of patients had worn glass spectacles for a majority of their lives, while the patients in the second group had never worn spectacles or had worn only reading glasses. Subjects in the group with spectacles showed significantly less development of sclerotic nuclear lens changes. These findings may be due to the screening effect by spectacle glass of light in the ultraviolet range and suggest that uv light may be one of the risk factors in the development of nuclear sclerotic cataracts.     

Calculating the error in refractive error

Aims and Purpose

To demonstrate a quick way of calculating the optical difference between two refractions using vector analysis, and to express this as a score for examination purposes.

Methods

An existing formula is applied, converted to a defocus equivalent, and then converted to a score. The formula is set out in an Excel spreadsheet.

Results

The spreadsheet enabled rapid assessment of the difference between two refractive errors. Examples are demonstrated.

Conclusion

The spreadsheet was successful in enabling a comparison of any two refractions, expressing the difference either as a correcting (third) refraction, a defocus equivalent or a one-figure score.     

Population prevalence of tilted optic disks and the relationship of this sign to refractive error

PURPOSE: To assess the prevalence of tilted disks and its association with refractive error and visual field defects. DESIGN: Population-based cohort study. METHODS: The Blue Mountains Eye Study examined urban Australians aged 49 years or older between 1992-1994. Of 4,433 eligible participants, 3,654 (82.4%) participated. The eye examination included logMAR visual acuity, standardized refraction, cover testing, stereoscopic optic disk photography, and Humphrey automated perimetry. Inferior or nasal optic disk tilting was graded from stereoscopic photographs. RESULTS: Of 3,583 participants with gradable photographs, inferior or nasal optic disk tilting was observed in 77 eyes of 56 participants (1.6%). The prevalence of tilted disks increased from 0.4% in eyes with astigmatism < 1.0 diopters to 17.9% in eyes with astigmatism >or= 5.0 diopters. The mean astigmatic error was 2.2 diopters in eyes with tilted disks compared with 0.7 diopters in eyes with normal disk appearance, P <.001. Myopia was present in 66.2% of eyes with tilted disks compared with 12.4% of eyes with a normal disk appearance, P <.001. The most common associated features were astigmatism (93.5%), pallor, and tessellation of the adjacent chorioretinal tissues (74.0%), situs inversus of the retinal vessels (70.1%), beta-peripapillary atrophy (64.9%), strabismus (30.4%), visual field defects (19.4%), posterior staphyloma (18.2%), inferonasal pigmentary accumulation (9.1%), and chorioretinal atrophy (5.2%). Superotemporal (33.3%) and superior (25.0%) visual field defects were most frequent. CONCLUSIONS: A tilted disk appearance was not a rare finding in our study population and was strongly associated with astigmatism and higher levels of spherical refractive error, particularly myopia. The tilted disk and its associated visual field defect should be distinguished from other sinister causes.     

Corneal asphericity and refractive error

The relationship between corneal curvature measured by classical keratometry and refractive error raises the question of a possible systematic relationship between refractive error and the degree of corneal asphericity. A recomputation and analysis of previously published data leads to the conclusion that the different refractive groups have similar values of the parameter 'p' and differ only in the apical radius of the cornea.     

Impact of short-term stopped-down spectacle wear on accommodation function

The impact of short-term stopped-down spectacle wear on accommodation function was studied in 32 patients with myopic refraction from 1.25 to 5.25 diopters (mean refraction 3.48 +/- 0.86 diopters). In all patients, laser refractometry was made monocularly at 5, 1, and 0.33 meters from the screen. A 0.33-m distance study revealed slight changes (a 0.06-diopter reduction) in the accommodation expenditure index. Dynamic refraction and accordingly the accommodation expenditure index changed to the greatest extent when a 1-m study was conducted. At the same time, there was a statistically insignificant reduction by 0.21-diopter. Our highly-sensitive studies of changes in ocular accommodation function during short-term stopped-down spectacle wear revealed no considerable changes in accommodation expenditure in patients with myopic refraction.     

Prevalence of spectacle and contact lens wear in the UK fire service

Despite the fact that firefighting has been shown to be a visually demanding occupation, the present visual standards for firefighters prohibit the use of spectacles or contact lenses operationally. To determine the proportion of the UK fire service currently using spectacles and contact lenses, and how many may benefit from optical correction, a questionnaire was distributed. This contained 30 questions and was sent to 1550 firefighters. The data from 1064 returned questionnaires have been analysed. The results show that approximately 20% of those serving in the fire service have used an optical correction at some time in their lives. When not working, approximately 6% of firefighters wear spectacles for distance vision and 15% wear them for reading. Only 0.4% of firefighters use contact lenses. Half of this contact lens wearing group use their lenses while on operational duty. In total, approximately 2% of firefighters use an optical correction for operational duties. The results indicate that a high visual standard at the time of entry into an occupation cannot guarantee good vision throughout an individual's career. In addition, an estimated 11 000 firefighters in the UK, who have spectacles or contact lenses, do not use them for operational duties. The present visual standards prevent this group of firefighters from obtaining their optimal visual performance at work.