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PubMed1999

Is refraction in early infancy a predictor of myopia at the age of 7 to 8 years? The relationship between cycloplegic refraction at 11 weeks and the manifest refraction at age 7 to 8 years in Chinese children.

Thirty-two children who had been refracted in early infancy were re-refracted at the age of 7 to 8 years. Refraction comprised cycloplegic retinoscopy at the mean age of 11 weeks and noncycloplegic retinoscopy and subjective examination at the mean age of 94 months. The change in spherical equivalent refraction (SER) was highly negatively correlated with the initial refraction (-0.863), demonstrating emmetropization; however, the correlation between the refractive error at age 7 to 8 years and the refractive error in infancy was much weaker (+0.225). The SER was significantly less and the astigmatism was greater in infancy in children who were myopic at age 7 to 8 years. There was, however, extensive overlap in range between the SER for the two groups and the initial SER was not a good predictor of myopia at 7 to 8 years, although it may help to identify children who are unlikely to become myopic. One hyperopic child with bilateral ptosis failed to emmetropize.

Aging↗
PubMed2005

The longitudinal orthokeratology research in children (LORIC) in Hong Kong: a pilot study on refractive changes and myopic control.

PURPOSE: Myopia is a common ocular disorder, and progression of myopia in children is of increasing concern. Modern overnight orthokeratology (ortho-k) is effective for myopic reduction and has been claimed to be effective in slowing the progression of myopia (myopic control) in children, although scientific evidence for this has been lacking. This 2 year pilot study was conducted to determine whether ortho-k can effectively reduce and control myopia in children. METHODS: We monitored the growth of axial length (AL) and vitreous chamber depth (VCD) in 35 children (7-12 years of age), undergoing ortho-k treatment and compared the rates of change with 35 children wearing single-vision spectacles from an earlier study (control). For the ortho-k subjects, we also determined the changes in corneal curvature and the relationships with changes of refractive errors, AL and VCD. RESULTS: The baseline spherical equivalent refractive errors (SER), the AL, and VCD of the ortho-k and control subjects were not statistically different. All the ortho-k subjects found post-ortho-k unaided vision acceptable in the daytime. The residual SER at the end of the study was -0.18 +/- 0.69 D (dioptre) and the reduction (less myopic) in SER was 2.09 +/- 1.34 D (all values are mean +/- SD). At the end of 24 months, the increases in AL were 0.29 +/- 0.27 mm and 0.54 +/- 0.27 mm for the ortho-k and control groups, respectively (unpaired t test; p = 0.012); the increases in VCD were 0.23 +/- 0.25 mm and 0.48 +/- 0.26 mm for the ortho-k and control groups, respectively (p = 0.005). There was significant initial corneal flattening in the ortho-k group but no significant relationships were found between changes in corneal power and changes in AL and VCD. CONCLUSION: Ortho-k can have both a corrective and preventive/control effect in childhood myopia. However, there are substantial variations in changes in eye length among children and there is no way to predict the effect for individual subjects.

Body Weights and Measures↗
PubMed2002

Remediation of refractive amblyopia by optical correction alone.

Amblyopia--the commonest vision abnormality of childhood--is characterized by a loss of visual acuity usually of one eye only. Treatment aims to promote function of the amblyopic eye and does this by restricting, usually through occlusion, the competitive advantage of the fellow eye. Recent experimental evidence demonstrates that the recovery of vision following early deprivation is facilitated by increasing visually evoked activity. An analogous approach in humans is to minimise image blur by correcting refractive error prior to treatment--a practice which may account for the poorly quantified improvements in visual acuity sometimes attributed to 'spectacle adaptation'. Here we describe clinically significant gains in visual acuity obtained over a period of 4-24 weeks in a group of amblyopic children arising solely in response to the correction of refractive error. Consequences for the clinical management of refractive amblyopia are discussed.

Amblyopia↗
PubMed1995

Hyperacuity test to evaluate vision through dense cataracts; research preliminary to a clinical study. I. Studies conducted at the University of California at Berkeley before travel to India.

BACKGROUND. Patients with dense ocular media disorders retain the ability to project or point to an intense source of light. Using this response capability and high luminance points of light as stimuli, Vernier judgments (a hyperacuity test) can be made by these patients, even without the presence of a "window" through a leucoma, cataract, or bleed. Without coaching, these individuals are able to locate the centers of the individual degraded point images if the individual light sources are adequately separated (i.e., if sufficient "gaps" exist between the individual stimuli), and they can spatially align the degraded images. Advanced cataracts are the main cause of blindness in the developing world, and this is a treatable condition. In these nations, only a modest proportion of affected patients receive surgery, and only 5% or less of these individuals obtain treatment in two eyes. There are incredibly large and rapidly growing backlogs of advanced cataract patients requiring care (many millions). Because of the 20 to 30% failure rates that occur after treatment (all causes) in many developing world settings, a test performed before surgery, which offers a meaningful estimate of postsurgical visual outcome, can be valuable. Using the principle defined above, we seek to determine before surgery those individuals who will derive most benefit from cataract removal, and which of two cataractous eyes has the better postsurgical visual prognosis. EXPERIMENTAL. In Berkeley, we performed a series of preliminary studies on a Vernier acuity test before initiating a clinical study in a developing world setting. These studies were conducted upon young adult normal subjects wearing their usual vision corrections, with and without induced refractive errors, and/or with or without simulated dense nuclear cataracts. We sought (1) to determine the number of repeat trials necessary for reliable outcomes; (2) to compare a two-point and a three-point Vernier acuity display; (3) to determine the shape of the measured response function at large gap separations between test points; (4) to define optimal test distance and stimulus size; (5) to assess the effect(s) of a broad range of uncorrected refractive errors upon outcomes; and (6) to consider means to minimize refraction-based errors by using a pinhole, a refractive correction, and/or selective spatial filtering. We compared responses obtained using the current CRT/VDT-based, computer-driven (Berkeley) instrument with a new precision optical/mechanical computer-driven (India) instrument. The India instrument is needed to determine design parameters for a next stage simpler, cheaper, more rugged field instrument(s).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1997

Infant emmetropization: longitudinal changes in refraction components from nine to twenty months of age.

Rapid emmetropization is described in pediatrically normal infants from 9 months of age during the following year. The infants, obtained from various categories of the Cambridge population screening program, provided a broad range of refractive errors. The large group of 254 nonanisometropic infants studied allowed the mean rate of change and dependence on the initial refraction value to be determined. Refraction was measured by cycloplegic retinoscopy. Rapid emmetropization changes occurred in the following refractive components: mean spherical equivalent (MSE), astigmatism magnitude, the horizontal astigmatism component, the infant's most positive meridian, and the infant's most negative meridian. The MSE and astigmatism rates of change (diopters/year), were highly dependent on their respective initial powers (r = -0.61 and r = -0.76). The percentage weighted mean proportional rate of change for MSE was -30% (SE 4%) and for astigmatism magnitude it was -59% (SE 14%). There was much individual variation, with some exhibiting fast emmetropization and others not. The MSE and astigmatism changes, however, were almost independent of each other. The refractive errors of the most positive and most negative meridians emmetropize because they are both derived from the MSE and half the astigmatism. With-the-rule astigmatism was more prevalent than against-the-rule astigmatism at 9 months of age, and with-the-rule astigmatism exhibited a significantly greater proportional rate of change. The relationship of emmetropization and refractive screening is considered. A new component "MOMS" is introduced, the maximum ocular meridional separation, when both eyes are considered. Thus incorporating astigmatism and anisometropia may be a good single indicator of conditions associated with later amblyopia. The almost independent emmetropization of the MSE and astigmatism components is an important result to consider in theories of emmetropization, refractive screening, clinical prescribing, and the evaluation of infants in treatment trials.

Accommodation, Ocular↗
PubMed1988

Peripheral refractive correction and automated perimetric profiles.

The effect of peripheral refractive error correction on the automated perimetric sensitivity profile was investigated on a sample of 10 clinically normal, experienced observers. Peripheral refractive error was determined at eccentricities of 0 degree, 20 degrees and 40 degrees along the temporal meridian of the right eye using the Canon Autoref R-1, an infra-red automated refractor, under the parametric conditions of the Octopus automated perimeter. Perimetric sensitivity was then undertaken at these eccentricities (stimulus sizes 0 and III) with and without the appropriate peripheral refractive correction using the Octopus 201 automated perimeter. Within the measurement limits of the experimental procedures employed, perimetric sensitivity was not influenced by peripheral refractive correction.

Adult↗
PubMed1996

Subjective refraction of the peripheral field using contrast detection acuity.

BACKGROUND: Although peripheral resolution acuity is relatively unaffected by uncorrected refractive error, recent investigations of peripheral vision indicate that contrast detection is optically limited. It should be possible, therefore, to perform a subjective refraction in the peripheral visual field using a contrast detection task. METHODS: For a range of trial lenses, contrast detection acuities for vertical and horizontal gratings were measured with a two-interval forced-choice paradigm. Lens powers that maximized detection acuity were taken as the subjective refraction estimates. These powers were compared with objective refractions determined with retinoscopy and autorefractometry. RESULTS: Contrast detection acuity varied significantly with lens power at all retinal locations tested. Defocusing by one diopter from the optimum lens power reduced detection acuity by about a factor of two at 20 degrees eccentricity, and slightly less in the far periphery. Objective retinoscopy and autorefractometry agreed with subjective measurements for most conditions tested. CONCLUSIONS: Contrast detection acuity in the peripheral visual field varies with refractive blur, demonstrating the feasibility of performing subjective refraction in the periphery for a contrast detection task. Results suggest that visual fields measured with standard perimetry, which is based on contrast detection, may be affected by uncorrected peripheral refractive errors.

Adult↗
PubMed2006

Refractive change in thyroid eye disease (a neglected clinical sign).

BACKGROUND/AIMS: The literature on refractive change in thyroid eye disease (TED) is limited. This study documents the refractive change in patients with TED undergoing orbital decompression. The authors propose possible mechanisms for their acquired refractive error. METHODS: This is a retrospective observational case study of five patients with progressive TED. Their detailed eye examinations including refractive state preoperatively and postoperatively are presented. RESULTS: An acquired hypermetropic shift with active TED before orbital decompression of up to 3.75 D spherical equivalent refraction (SER) is reported in one patient. Post-orbital decompression, an induced myopic shift of between 1.00-2.50 D SER for all patients is observed, noted to range from 1 day following surgery to up to 9 months, dependent on the availability of data. Axial length increased in two cases corresponding to postoperative myopic shift. Magnetic resonance imaging findings of one patient demonstrate flattening of the posterior pole as a cause of the acquired preoperative hypermetropia. CONCLUSIONS: TED has a significant effect on the refractive state of patients. The proposed mechanism of acquired hypermetropia relates to increased volume of orbital contents with flattening of the posterior globe. This is reversed with successful orbital decompression. Documentation of refractive error in all cases of progressive TED is recommended. Progressive acquired hypermetropia may be suggestive of TED activity.

Adult↗
PubMed2006

Costs of refractive correction of distance vision impairment in the United States, 1999-2002.

OBJECTIVE: Correctable vision impairment caused by refractive error is common in the United States population. We estimated the direct costs of providing eyeglasses to all Americans (age> or =12) who need refractive correction to achieve good distance vision. DESIGN: Cross-sectional study of a nationally representative sample of United States citizens. PARTICIPANTS: Participants in the 1999-2002 National Health and Nutrition Examination Survey (NHANES), age > or = 12 years. The NHANES examines a nationally representative sample of the U.S. noninstitutionalized, civilian population. METHODS: Presenting and corrected visual acuity data were obtained using an autorefractor from 13,211 (93.0%) of the 14,203 participants who visited the NHANES Mobile Examination Center in 1999 through 2002. Need for refractive correction was defined by current use of corrective lenses for distance vision, improvement to good visual acuity following autorefractor correction (using several cutpoints to define good visual acuity), or both. MAIN OUTCOME MEASURES: Estimates of direct cost for refractive correction (1 pair of complete eyeglasses and a refraction examination) were computed based on Centers for Medicare & Medicaid Services fee schedules for 2000 and also based on expenditure data from the Medical Expenditure Panel Survey. RESULTS: The NHANES results indicate that >110 million Americans could or do achieve normal vision with refractive correction. The annual direct cost of correcting distance vision impairment is at least $3.8 billion. Of this amount, $780 million represents the annual cost of providing distance vision correction for persons > age 65. CONCLUSIONS: Correctable vision impairment due to refractive error is common in the United States population. These cost estimates provide useful information for public health endeavors aimed at provision of refractive correction to those who need it.

Adolescent↗
PubMed2004

Childhood myopia and parental smoking.

AIM: To examine the relation between exposure to passive parental smoke and myopia in Chinese children in Singapore. METHODS: 1334 Chinese children from three schools in Singapore were recruited, all of whom were participants in the Singapore Cohort study Of the Risk factors for Myopia (SCORM). Information on whether the father or mother smoked, number of years smoked, and the number of cigarettes smoked per day during the child's lifetime were derived. These data were correlated with contemporaneously obtained data available in SCORM. The children's cycloplegic autorefraction, corneal curvature radius, and biometry measures were compared with reported parental smoking history. RESULTS: There were 434 fathers (33.3%) and 23 mothers (1.7%) who smoked during their child's lifetime. There were no significant trends observed between paternal smoking and refractive error or axial length. After controlling for age, sex, school, mother's education, and mother's myopia, children with mothers who had ever smoked during their lifetime had more "positive" refractions (adjusted mean -0.28 D v -1.38 D) compared with children whose mother did not smoke (p = 0.012). CONCLUSIONS: The study found no consistent evidence of association between parental smoking and refractive error. There was a suggestion that children whose mothers smoked cigarettes had more hyperopic refractions, but the absence of a relation with paternal smoking and the small number of mothers who smoked in this sample preclude definite conclusions about a link between passive smoking exposure and myopia.

Child↗
PubMed1992

Eyeglass use by U.S. Navy jet pilots: effects on night carrier landing performance.

The purpose of this study was to test the hypothesis that the night carrier landing performance of pilots who do not need prescriptive eyeglasses to fly is better than the performance of pilots who do. Night carrier landing scores (NCLS), age, career jet flight hours, and total career flight hours were obtained for 122 U.S. Navy fighter pilots participating in air combat maneuver training at NAS, Oceana, VA. of the pilots with NCLS, 16 used a prescribed spectacle correction while flying, 106 did not. This study compared the NCLS of the two groups of pilots, those with glasses and those without. We found no significant difference in NCLS between the two groups of pilots--even when the pilots were matched on the basis of age and flight experience. We conclude that pilots who have a refractive error and are required to wear an eyeglass correction while flying perform night carrier landings as well as the pilots who have no refractive error and are permitted to fly with no eye glass correction.

Adult↗
PubMedDate not supplied

Intraocular lens implantation and laser in situ keratomileusis (bioptics) to correct high myopia and hyperopia with astigmatism.

PURPOSE: To analyze the refractive outcome of moderate to high myopic and hyperopic patients with astigmatism who underwent programmed refractive surgery; first lens phacoemulsification with intraocular lens implantation and 3 months later, laser in situ keratomileusis (LASIK). METHODS: Four men and eight women (22 eyes) with a mean age 47.3 years (range, 38 to 75 yr), and an average spherical equivalent refraction of -11.76 D and +5.22 D and (range, -17.50 to +8.50 D) underwent two refractive procedures. First, phacoemulsification of the lens with a self-sealing incision through clear cornea on the steepest topographic axis and implant of a monofocal intraocular lens in the bag was performed by two experienced surgeons. Second, LASIK was performed with the Nidek EC-5000 excimer laser and the Moria LSK-One microkeratome, by one surgeon. Eyes were divided into two different groups. In the first group, the IOL implanted was calculated to leave the eye slightly myopic, with final correction to be achieved with LASIK. In the second group, the IOL implanted was calculated to achieve emmetropia, correcting any residual refractive error with the laser. RESULTS: After surgery, mean spherical equivalent refraction was +0.26 D (range, -0.375 to +1.50 D). Predictability of refractive outcome: 0 to -1.00 D, 63.63%; +0.25 to +1.00 D, 31.80%; +1.25 to +2.00 D, 4.54%. Mean residual refractive astigmatism was 0.30 D (range, 0 to 1.50 D). Uncorrected visual acuity of 20/20 or better was achieved in 18.3% of eyes; 20/40 or better in 81.8%. No eyes lost two or more Snellen lines of visual acuity and no adverse effects were observed. CONCLUSIONS: Bioptics (phacoemulsification with IOL implantation followed 3 months later by LASIK with the Nidek EC-5000 excimer laser) for correction of moderate to high myopia and hyperopia, with astigmatism, enabled us to treat the total refractive error and adjust final outcomes.

Adult↗
PubMed1987

A comparison of cycloplegic and manifest refractions on the NR-1000F (an objective Auto Refractometer).

The manifest (dry) and cycloplegic refractions of 50 eyes of 25 patients aged 8 to 28 years were studied on the Nikon Auto Refractometer NR-1000F (AR) and compared with the results of clinical refraction (CR) under homatropine and the final clinical acceptance on postmydriatic testing. Only patients in the younger age groups with low to moderate refractive errors were included in this study; high myopes and hypermetropes and patients with aphakia and mixed astigmatism were excluded. The degree of agreement for spherical equivalents, sphere components, and cylinder components was analysed separately for both cycloplegic and manifest refractions on the AR and CR. The results showed that the fixation target in the NR-1000F induces significant instrument myopia during manifest refraction in the younger patients with lower refractive errors. We recommend that caution should be exercised in interpreting manifest refractions on the AR, especially in younger patients. A cycloplegic automatic refraction would be acceptably accurate.

Adolescent↗
PubMed2001

Randomized comparison of diode laser photocoagulation versus cryotherapy for threshold retinopathy of prematurity: seven-year outcome.

PURPOSE: To report the structural and functional outcomes at a minimum of 7 years postmenstrual age after randomized treatment of threshold retinopathy of prematurity with laser ablation or cryotherapy. METHODS: Nineteen patients were entered into a prospective, randomized protocol, in which one eye received cryotherapy, while the other eye received diode laser photocoagulation. Asymmetric eyes were randomly assigned. Two patients have died, and seven were no longer available for 7-year outcome examinations, leaving 10 children for analysis. RESULTS: Six males and four females with a mean birthweight of 631 g and a mean gestational age of 24.8 weeks were examined. Eight were symmetrical cases and treated in both eyes. Of these, there were six concordant and two discordant structural outcomes. The laser-treated eyes had the favorable outcome in each instance. The geometric mean visual acuity of the paired eyes after laser photocoagulation was 20/33, and after cryotherapy it was 20/133 (P =.03). The mean refractive error was -6.50 diopters after laser photocoagulation and -8.25 diopters after cryotherapy (P =.27), although one of the cryotherapy eyes could not be refracted because of phthisis. CONCLUSIONS: Laser photocoagulation appears to be associated with a structural and functional outcome at least as good as cryotherapy 7 years after therapy. Visual acuity and refractive error data suggest that laser photocoagulation may have an advantage over cryotherapy.

Cryotherapy↗
PubMed1995

The equivalent refractive index of the crystalline lens in childhood.

Despite the importance of crystalline lens power in ocular development, schematic refractive index values used to calculate lens power have been validated for children. We measured refractive error and ocular component dimensions in 519 schoolchildren, calculating lens power using phakometrically measured lens radii and three different refractive index profiles: (1) Gullstrand-Emsley schematic indices [Gullstrand-Emsley lens power (GELP)]; (2) a 10-shell gradient index model [gradient index lens power (GILP)]; and (3) the equivalent refractive index (IND) needed to bring calculated and measured refractive error into agreement [calculated lens power (CLP)]. GELP was significantly lower than either GILP or CLP, indicating the Gullstrand-Emsley refractive index of 1.416 is too low for use in children. Variation in IND cannot be explained by measurement error alone. GILP and CLP also differed as a function of lens shape, with GILP greater than CLP at steeper external curvatures and less than CLP at flatter external curvatures. Variation in equatorial gradient index profile as a function of lens shape is proposed as an explanation for this bias. Equivalent index appears to be a useful tool for encompassing individual variation in lens gradient profiles as well as for assessing the relative role of lens surface curvature and refractive index changes during lens power development in childhood.

Adolescent↗
PubMedDate not supplied

Off-axis wave front measurements for optical correction in eccentric viewing.

In a previous study we have shown that correction of peripheral refractive errors can improve the remaining vision of subjects with large central visual field loss. Measuring peripheral refractive errors with traditional methods is often difficult due to low visual acuity and large aberrations. Therefore a Hartmann-Shack sensor has been designed to measure peripheral wave front aberrations in subjects using eccentric viewing. The sensor incorporates an eye tracker and analyzing software designed to handle large wave front aberrations and elliptic pupils. To ensure that the measurement axis is aligned with the direction of the subject's preferred retinal location, a special fixation target has been developed. It consists of concentric rings surrounding the aperture of the sensor together with a central fixation mark along the measurement axis. Some initial measurements on subjects using eccentric viewing have been performed successfully. As a first step in improving the peripheral optics of the eye, the wave front has been used to calculate the eccentric refraction. This refraction has been compared to the refraction found with the PowerRefractor instrument. Measuring the off-axis wave front is a fast way to assess the optical errors in the subject's eccentric viewing angle and to better understand the problems of eccentric correction.

Equipment Design↗
PubMed1982

The selection of intraocular lens power by calculation and by reference to the refraction--a clinical study.

Two hundred eyes each received a Rayner Binkhorst pupil-supported intraocular lens (IOL) after cataract extraction. One hundred received a standard power +19 D IOL and one hundred received an IOL of power calculated for emmetropia by the formula of R. D. Binkhorst using biometric data. Calculation reduced the incidence of postoperative refractive error greater than the +/- 2 D range from 20 per cent to 1 per cent virtually eliminating significant postoperative refractive error. Consideration of the preoperative refractions and the calculated IOL powers showed that there is no constant or reliable relationship. Twenty nine 'emmetropic' eyes were shown not to be 'normal' eyes but eyes with a wide range of axial lengths whose different optical components summated to give emmetropia. In the selection of IOL power, reference must be made to biometric data to allow for these optical components and for this reason IOL power cannot be determined from the preoperative refraction of the eye. The case for control of postoperative refraction by calculation of IOL power is a strong one and there appears little justification for the use of standard power IOLs with unpredictable refraction results.

Humans↗
PubMedDate not supplied

Visual status of industrial workers.

Two hundred and eighty four industrial workers were screened to determine their visual acuity. Significant visual impairment was observed in 21.8% individuals and moderate impairment in 34.5% of cases. Convergence insufficiency was a problem in 9.86% of the workers. Since uncorrected refractive errors are a prelude to disastrous workplace related eye injuries, it is recommended that prior to job placement all workers undergo visual acuity screening and get their refractive errors rectified.

Adult↗