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PubMed2001

Retinoscopy in infants using a near noncycloplegic technique, cycloplegia with tropicamide 1%, and cycloplegia with cyclopentolate 1%.

PURPOSE: This study compares retinoscopy in infants using a near noncycloplegic technique, cycloplegia with tropicamide 1%, and cycloplegia with cyclopentolate 1%. The study sample included 29 healthy, nonstrabismic infants 4 to 7 months of age (mean 5.71 months). METHODS: Each study subject was examined at two separate visits an average of 2 weeks apart (mean [+/-SD] 14 +/- 9 days). The examiner completed a case history, iris color grading, confrontation tests, and noncycloplegic near retinoscopy in a dark room and then instilled a drop of topical anesthetic in each eye followed by 2 drops of cycloplegic agent separated by 5 min. Retinoscopy was performed 25 to 30 min after the first drops were instilled. The bottles were masked, and the drop administered at the first visit was randomly assigned. RESULTS: On a scale of 0 to 4.9, the median iris grade was 4.0, which corresponds to a brown or darkly pigmented iris. All reported retinoscopy results are for the horizontal meridian of the right eye. The mean refractive error using noncycloplegic near retinoscopy was +0.94 D (+/-1.19 D). The mean refractive error was +1.81 D (+/-1.19 D) with tropicamide and +1.88 D (+/-1.45 D) with cyclopentolate. There was no statistically or clinically significant difference between the two cycloplegic measurements using different diagnostic agents (t = -0.46, p = 0.65). The mean difference between noncycloplegic and cycloplegic retinoscopy was 0.89 D (+/-0.66 D) with tropicamide (t = -6.57, p < 0.0001) and 1.04 D (+/-0.94 D) with cyclopentolate (t = -5.38, p < 0.0001; all two-sided paired t-tests). There were no serious adverse reactions with either agent, although one infant temporarily developed redder than normal cheeks after instillation of cyclopentolate. CONCLUSION: Our results suggest that tropicamide is as effective as cyclopentolate for the measurement of refractive error in most healthy, nonstrabismic infants.

Ciliary Body↗
PubMed1997

Visual anomalies in young children exposed to cocaine.

PURPOSE: The number of children exposed to cocaine in utero each year is increasing. Recent reports suggest significant visual anomalies in infants prenatally exposed to cocaine. The purpose of this retrospective study was to determine if children exposed prenatally to cocaine were at a greater risk for visual abnormalities, such as strabismus and significant refractive errors. METHODS: This pilot study was conducted at two sites, an outpatient clinic and a hospital-based practice. Consecutive files from January to July, 1993, of 79 children (aged 4 months to 94 months); who were identified by case history or meconium analysis information as being exposed to cocaine in utero, were reviewed. Fifty-five children met the inclusion criteria for the study. In addition, a control group of 100 pediatric patients were randomly selected from the pediatric patients seen at the outpatient clinical site. RESULTS: Of the 30 children from the Illinois Eye Institute (IEI) and the 25 children from The Children's Hospital (TCH), spherical refractive errors in the right eye ranged from +6.50 to -12.50 D. The median refractive errors were +0.75 and +0.50 D, respectively. No statistical difference was found in spherical refractive error, astigmatism, or anisometropia between the cocaine-exposed cohorts and the control group (N = 100). Strabismus was found in 15/55 (27%) of the children in the cocaine-exposed group. There was a statistically significant difference in the prevalence of strabismus between the cocaine-exposed group and the control group. Further analysis revealed that full birthweight (> 2500 g) children prenatally exposed to cocaine were at a greater risk for strabismus as compared to the full birthweight control group. Ocular abnormalities were rare, but included optic nerve atrophy and retinopathy of prematurity. CONCLUSIONS: These data suggest cocaine exposure during pregnancy may place a child at risk for conditions that may negatively impact the visual system, specifically strabismus.

Abnormalities, Drug-Induced↗
PubMed2006

Analysis of refractive state ratios and the onset of myopia.

PURPOSE: To develop formulae for the refractive state ratios, axial length growth and the age of onset (A*) of myopia. Calculated results are compared with measurements. METHODS: Using an image equation, the axial length in the ametropic state (L) is related to the length in the emmetropic state (L*) and refractive error (D) by a rate of change M (D mm(-1)). Three refractive state ratios are defined: C1 = L/r1, C2 = L/L* and C3 = L/H, where r1 and H are the anterior surface radius of the cornea and the transverse dimension of the eye, respectively. The age of onset A* is calculated by the rate of change of refractive error (M) and the axial growth rates N and N* in the ametropic and emmetropic states, respectively. RESULTS: The three ratios C1, C2 and C3 are increasing function of the myopia power, for example, C1 = 3.4, 3.1, 2.9 for D = -8, 0, +4 dioptres, respectively. The calculated C1* (for the emmetropic state) varies between 3.08 and 3.14, depending on corneal shape, and C3 = 0.985, 1.0, 1.04 for D = +3, 0, -3 dioptres: these values are consistent with measured data. For a typical system with effective focal length F = 22.25 mm, L* = 24.2 mm and L = 23.4, 24.9, 25.9 mm for D = +2, -2, -5 dioptres, respectively. The calculated rates of change of refractive error M = 2.3-2.9 D mm(-1) for F = 22-23 mm are also consistent with measured values 2.4-2.7 D mm(-1). The age of onset A* is calculated to be proportional to 1/(M dN), where dN = N-N* is the axial growth rate difference between the ametropic and emmetropic states and may be used as a better predictor for myopia onset than the conventional ratio L/r1. The A* is given by the crossing of L and L* curves, in which myopia onset occurs earlier for larger M dN. CONCLUSION: The theory provides formulae to calculate various refractive state ratios, which are consistent with measurements. By defining two rate functions, M and N, the onset of myopia can be predicted.

Age of Onset↗
PubMed2006

[Results of 10 years observation of organ of sight in prematurity].

PURPOSE: (1) To compare the incidence of refractive errors and the orthoptic condition in ten-year-old children, born prematurely and treated with cryotherapy versus children, whom did not apply such a procedure. (2) To estimate condition of the extraocular muscles. MATERIAL AND METHODS: A group of 60 prematurely born children was divided into 2 subgroups: I--30 children treated with cryotherapy, II--30 no treatment was applied. All the children had anterior segment, fundus and visual acuity examined. Refraction following cycloplegia was evaluated. Visual acuity and orthoptic status was assessed. RESULTS: In the group of prematurely born children who had retinopathy in the infantile age and were treated with cryotherapy, refractive errors were frequently observed. In over half of those children squint or impaired eye movement were found. In the group of children who required no cryotherapy the percentage of those with refractive errors was similar. CONCLUSIONS: In prematurely born children with retinopathy refractive errors and squint occur quite often. Prematurely born children should be subject to ophthalmologic follow-up throughout their childhood.

Child↗
PubMed1994

The age of onset of posterior vitreous detachment.

The age of onset of posterior vitreous detachment (PVD) was studied in 930 eyes with a clearly defined onset time and no vitreoretinal diseases except refractive error or equatorial degeneration. We found a positive correlation between onset age of PVD and refractive error, with the regression line y = 0.91 x + 60.93 (y onset age, x diopter of refractive error). The higher the degree of myopia, the younger the onset age of PVD. Comparing onset ages for 240 eyes from males and 690 eyes from females, there was a possible tendency toward a lower PVD onset age for females. There was no significant difference in onset age between 112 eyes with and 818 eyes without equatorial degeneration of the retina.

Adult↗
PubMed1998

Hyperopia is predominantly axial in nature.

PURPOSE: Myopia has been found to be predominantly axial in nature, i.e. myopic eyes have longer than normal axial lengths, with corneal radius variations having only a small influence on the magnitude of the refractive error. In this study we assess whether a similar relationship exists for hyperopia. METHODS: Biometric data were collected on 57 subjects with either emmetropic or hyperopic refractive errors ranging in magnitude from -0.37 D to +17.25 D. Our main analysis concentrated on subjects with less than +10 D of hyperopia (group 1, n = 53), as subjects with +10 D of hyperopia or more (group 2, n = 4) exhibited marked differences in their biometric characteristics. RESULTS: Analysis of group 1 data revealed a significant relationship (r2 = 0.611, p = 0.0001) between the degree of hyperopia and the measured axial lengths. A weak but statistically significant relationship (r2 = 0.128, p = 0.009) was also found between mean corneal radius measures and mean spherical refractive errors, with the mean corneal radius flattening with increasing hyperopia. In group 2, three of the four subjects exhibited much steeper corneal characteristics than predicted from the group 1 data. CONCLUSIONS: Our results suggest that hyperopia, like myopia, is predominantly axial in nature, although the corneal radius also plays a role in determining refractive error magnitude. These results have implications for refractive surgery and visual performance in hyperopic eyes.

Adolescent↗
PubMed1998

Ophthalmological long-term follow up of preterm infants: a population based, prospective study of the refraction and its development.

BACKGROUND: Numerous studies have reported an increased risk of refractive errors in prematurely born infants, but only few have been long-term and strictly population based. METHODS: A 3.5 year ophthalmological long term follow up of 248 preterm infants was performed. The infants had been included in a previous epidemiological study of retinopathy of prematurity (ROP) (birth weight < or = 1500 grams). The incidence of refractive errors and development of refraction were studied, based on retinoscopies at 6 and 30 months of corrected age. RESULTS: The overall incidence of myopia was 8% at 6 months, of which 35% was transient, and 10% at 30 months. Of the cryotreated infants, 30-40% were myopic at both retinoscopies. The incidence of astigmatism was 52% at 6 months and 26% at 30 months. Astigmatism was associated with ROP, but not with cryotreated ROP itself. Astigmatism "against the rule" was commoner than astigmatism "with the rule". Anisometropia occurred in 6.5% of the infants at 6 months and in 8.4% at 30 months. The incidence of anisometropia was higher in eyes with ROP, particularly in cryotreated eyes, which tended to have high and persistent anisometropia. CONCLUSION: The risk of refractive errors is higher in preterm infants than in infants born at term, and also prematurely born infants without ROP do run an increased risk of having myopia and anisometropia. We recommend follow up examinations with retinoscopy for all infants included in screening programmes for ROP.

Anisometropia↗
PubMed2003

Continuous ambient lighting and lens compensation in infant monkeys.

PURPOSE: Protracted daily lighting cycles do not promote abnormal ocular enlargement in infant monkeys as they do in a variety of avian species. However, observations in humans suggest that ambient lighting at night may reduce the efficiency of the emmetropization process in primates. To test this idea, we investigated the ability of infant monkeys reared with continuous light to compensate for optically imposed changes in refractive error. METHODS: Beginning at about 3 weeks of age, a hyperopic or myopic anisometropia was imposed on 12 infant rhesus monkeys by securing either a -3 D or +3 D lenses in front of one eye and a zero-powered lens in front of the fellow eye. Six of these monkeys were reared with the normal vivarium lights on continuously, whereas the other six lens-reared monkeys were maintained on a 12-h-light/12-h-dark lighting cycle. The ocular effects of the lens-rearing procedures were assessed periodically during the treatment period by cycloplegic retinoscopy, keratometry, and A-scan ultrasonography. RESULTS: Five of six animals in each of the lighting groups demonstrated clear evidence for compensating anisometropic growth. In both lighting groups, eyes that experienced optically imposed hyperopic defocus (-3 D lenses) exhibited faster axial growth rates and became more myopic than their fellow eyes. In contrast, eyes treated with +3 D lenses showed relatively slower axial growth rates and developed more hyperopic refractive errors. The average amount of compensating anisometropia (continuous light, 1.6 +/- 0.5 D vs. control, 2.3 +/- 0.5 D), the structural basis for the refractive errors, and the ability to recover from the induced refractive errors were also not altered by continuous light exposure. CONCLUSION: Ambient lighting at night does not appear to overtly compromise the functional integrity of the vision-dependent mechanisms that regulate emmetropization in higher primates.

Animals↗
PubMed1990

[Epikeratophakia].

Since its introduction by Kaufman in 1979, epikeratophakia has been used successfully in several thousands of patients for the correction of refractive errors. With this technique the original curvature of the cornea is changed by suturing onto it a preshaped lenticule. Depending on the different types of refractive errors to be corrected, the tissue lens is a plus lens (aphakia, hyperopia), a minus lens (myopia), or a plano lens (keratoconus). Both prelated, lyophilized tissue lenses and freshly cut lenticules have been employed with good results. However, the simplicity of the surgical technique, as well as the possibility of rejection of fresh corneal tissue, has made use of the former type of epikeratophakia lenses much more common. The basic indication for epikeratophakia is the incapability of correcting refracting errors with conservative methods, such as glasses, contact lenses or, in cases of aphakia, intraocular lenses. The results obtained in a series of 71 patients who underwent epikeratophakia at our Institute compare favorably to those reported in the literature. Following are some of the factors we identified as being responsible for our improved results: (1) the performance of all surgical procedures by the same corneal surgeon; (2) a longer hospitalization period and thereby closer observation of all patients and possible detection of early complications; (3) long-term postoperative follow-up examinations of all patients by the operating surgeon. In summary, epikeratophakia has been shown to be a safe, effective and potentially reversible procedure for the correction of refractive errors.

Cornea↗
PubMed1981

Racial variations in vision.

This study determined the distributions of uncorrected visual acuity and of refractive error in representative groups of Australian Aborigines and Australians of European origin aged 20-30 years. The methodology used in this study and its verification are described in detail. As a group, the Aborigines have significantly better visual acuity than the Europeans. This was true for both monocular and binocular vision. Some Aborigines have acuities below the previous postulated threshold levels. Aborigines as a group also have the previous postulated threshold levels. Aborigines as a group also have less myopia--in particular, less high myopia--and less astigmatism than Europeans. The mean refraction for Aborigines is about half a diopter more hypermetropic than that for Europeans, although there is not an excess of high hypermetropia in Aborigines. The lack of high refractive errors suggests that the Aborigines may not possess the genes that cause abnormal axial lengths usually associated with high refractive errors in Europeans. The superior vision of the Aborigines persisted, however, when comparing groups which were essentially emmetropic. Therefore, it appears to be a true racial difference which is not explicable on the grounds of variation in refractive error but may result from finer retinal organization or better cerebral integration of visual stimuli.

Australia↗
PubMed2006

Orthokeratology review and update.

Orthokeratology (OK) is a clinical technique that uses specially designed rigid contact lenses to reshape the cornea to temporarily reduce or eliminate refractive error. This article reviews the history of traditional daily-wear OK (1960s to 1980s) and discusses the reasons for the recent resurgence in interest in the new modality of overnight OK, using reverse-geometry lens designs (1990s to the present). The clinical efficacy of the current procedure is examined and outcomes from clinical studies in terms of refractive error change and unaided visual acuity are summarised. Onset of the effects of overnight OK lens wear is rapid, with most change after the first night of lens wear and stability of refractive change after seven to 10 days. Mean reductions in myopic refractive error of between 1.75 and 3.33 D and individual reductions of up to 5.00 D have been reported. There appear to be slight reductions or minimal changes in astigmatism with the use of reverse-geometry lenses and most patients are reported to achieve 6/6 unaided vision or better. The induction of higher order aberrations, in particular, spherical aberration, has been reported and this may affect subjective vision under conditions of low contrast and pupil dilation. Patient satisfaction with overnight OK has been reported as similar to or better than with other popular modalities of contact lens wear. Available evidence suggests that the corneal changes induced by overnight OK are fully reversible. The refractive effect in OK is achieved by central epithelial thinning and this has raised concerns about compromise of the epithelial barrier to microbial infection. Recent reports of microbial keratitis in the modality are reviewed and the overall safety of the procedure is examined critically. Recent research on stromal contributions to the OK effect, particularly relating to overnight oedema, is summarised. Emerging issues in OK, including myopic control, correction of other refractive errors and permanency of the OK effect, are discussed.

Contact Lenses↗
PubMed2005

Need and challenges of refractive correction in urban Chinese school children.

PURPOSE: Uncorrected refractive error is recognized as the principal cause of visual impairment in school-aged children. Although correction of refractive error is easy, safe, and effective, many children are without the necessary spectacles. Empiric research on barriers to refractive correction remains limited, precluding the formulation of effective remedial actions. The aims of this study were to characterize parental awareness and other barriers to spectacle use among children considered to be in need of refractive correction and to determine the proportion undercorrected for those already with spectacles. METHODS: A population-based sample of children 5 to 15 years of age was examined in Guangzhou, China. Visual acuity was measured followed by cycloplegic refraction and best-corrected vision. Parental awareness of the child's vision difficulties, spectacle use, and frequency of vision checkups were collected by questionnaire. Associations between these variables and demographic and socioeconomic characteristics were investigated with multiple logistic regression. RESULTS: Among the 4359 examined children, 919 (21.1%) were found to be in need of refractive correction. Need was defined as uncorrected visual acuity < or = 0.50 in both eyes correctable by at least two lines in the better eye. Parental awareness was apparent for 85% of cases; 74% had spectacles. Awareness of vision difficulties was associated with older child age, greater visual impairment, and higher parental education. The purchase of spectacles was associated with greater visual impairment; the child's age, gender, parental education, and family income were not significant factors. Undercorrection by two lines or more in the better eye was found in 30% of those already with spectacles; undercorrection was associated with greater visual impairment and less frequent refraction checkups. CONCLUSIONS: Half of the children in need of first-time or updated spectacles are without them, an unacceptably high proportion. Younger children with moderate visual impairment are at particular risk for uncorrected refractive error. Parental education and enhanced school-based screening programs may be necessary to address the unfilled need for refractive correction among school-aged children.

Adolescent↗
PubMedDate not supplied

Predicting visual performance following excimer photorefractive keratectomy.

BACKGROUND: A duplex optical image is created when the ablation zone formed by excimer photorefractive keratectomy is smaller than the entrance pupil. Visual performance and secondary effects are analyzed using a theoretical model of the optical image. METHODS: A point-spread function having a centered in-focus component surrounded by an annular out-of-focus component is calculated from pupil size, ablation size, refractive error, and photoreceptor directional sensitivity. The line-spread, edge-spread, and optical transfer functions are derived. RESULTS: In the line- and edge-spread functions, secondary maxima and curvilinear ramps are most evident with low refractive errors. The half-height widths of the point- and line-spread functions change little. The optical transfer function is reduced in proportion to the distribution of light between the image components. CONCLUSIONS: Stable point and line half-height widths explain why Snellen visual acuity is insensitive to annular blur. Contrast sensitivity correlates with symptoms of haze and fog. Halos and ghost images are associated with secondary optical maxima and curvilinear ramps. Neither visual acuity nor contrast sensitivity can predict halos or ghost images. Halos and ghost images will be most prevalent in low illumination and for low refractive corrections. High refractive errors will produce fewer visual side effects than low refractive errors.

Contrast Sensitivity↗
PubMed2004

[Changes in the static visual field of patients with low and medium myopia].

UNLABELLED: Myopia is associated with many diverse changes in the structure and function of the eye. Determination of the visual field belongs to the diagnostic arsenal used for detection and monitoring of such alterations. It is well established that myopia is accompanied by changes in the kinetic visual field. Recently, static visual field examinations are gaining wider acceptance as they represent the most sensitive and reliable approach to early changes in myopia. However, only a few papers on static perimetry in myopia have been published and the results are conflicting. No publications have appeared in Polish medical press. Therefore, we decided to investigate which alterations occur in the static visual field of patients with myopia. We enrolled 32 men and 58 women (180 eyes) aged 19 to 34 (mean 23 years) and formed three groups (I-III) of 30 subjects each: (I) control (without any refractive anomaly); (II) low myopia (average refractive error -2.0 D sph. +/- SD of 1.0); and (III) medium myopia (average refractive error -5.6 Dsph +/- SD of 1.2). Myopia was defined as a refractive error of value < or = -0.5 D, with low myopia not exceeding 4.0 D, and medium myopia between -4 and -8 D. Inclusion criteria were: full visual acuity with/without correction, astigmatism < 0.75 D cyl., intraocular pressure < 21 mm Hg, and no eye pathology other than myopia. A full panel of ophthalmologic tests was carried out, including repeat static perimetry (central 30 degrees) with Medmont M600 perimeter. Appropriate lenses were used during the tests. Average Defect (AD), Pattern Defect (PD), Mean Sensitivity (MS), and Fluctuation (F) values were recorded. Static visual field was assessed with the repeat examination only. Spearman's rank correlation coefficient, Kendall's tau, Gamma and linear correlations were analyzed. P values of less than 0.05 were considered statistically significant. A reduction in AD among subjects with low (P < 0.03) and medium (P < 0.03) myopia was found. There were no significant alterations in PD (Tab. 1). Elevation of myopia leads to reduction in AD (P < 0.0003) (Fig. 1), reduction in MS (P < 0.004) (Fig. 2), as well as increase in F (P < 0.04) (Fig. 3). CONCLUSION: Low and medium myopia may produce significant alterations in the visual field.

Adult↗
PubMed1999

Factors affecting the central corneal thickness of Hong Kong-Chinese.

PURPOSE: The aims of this study were to investigate the effect of age, intraocular pressure, refractive error (spherical equivalent) and corneal curvatures on the central corneal thickness of Hong Kong-Chinese. We also compared the central corneal thickness of Hong Kong-Chinese with those previously reported for other national/ethnic groups. METHODS: The central corneal thicknesses of 151 subjects of age 10-60 yrs were measured using an ultrasound pachometer. Intraocular pressure, refractive error and the corneal curvatures of these subjects were also recorded. RESULTS: The mean +/- SD central corneal thickness of the right eye and left eye were 575 +/- 32 microm and 574 +/- 31 microm respectively. No significant difference in central corneal thickness was found between the right and left eyes or between male and female subjects. Central corneal thickness decreased with increasing age but the effect appeared to be due to differences in female subjects only. The maximum decrease in central corneal thickness occurred in subjects in the age group of 10-25 yrs, and in this age group, central corneal thickness and age was significantly correlated in both male and female subjects. Intraocular pressure and central corneal thickness was significantly correlated. There was no correlation between central corneal thickness and refractive error or between central corneal thickness and corneal curvatures. CONCLUSIONS: Central corneal thickness decreased with increasing age but this appeared to be due to female subjects only. Central corneal thickness was significantly correlated with intraocular pressure, but not with refractive error or corneal curvatures. Our subjects also had significantly thicker corneas than those reported for Caucasian subjects.

Adolescent↗
PubMed1989

Visual assessment of the multiply handicapped patient.

The visual capabilities of the multiply handicapped and/or developmentally delayed patient are difficult to assess with methods that depend on the patient's subjective responses. Fifty-nine patients with multiple neurological handicaps and unknown visual capabilities were examined using a modified ophthalmic examination which included visual acuity measures using visual evoked potential (VEP) and preferential looking (PL) techniques. Patients ranged in age from 3 to 33 years; median age 9 years. Significant refractive error (in 73%) and strabismus (in 71%) were the most common ocular disorders. Of the 43 patients with a significant refractive error, only 16 (37%) were wearing their proper correction (ranging from -21 to +20 D). In 27 patients the uncorrected refractive error ranged from -10 to +20 D. Binocular acuities (with refractive correction) could be obtained from 56 patients (95%) using a spatial frequency sweep VEP technique, and in 41 patients (70%) using PL grating acuity cards. The VEP and PL grating acuity measures agreed to within 1 octave (a factor of 2 in minimum angle of resolution) in 27 of 41 patients. VEP acuity was 1.1 to 2.7 octaves higher in 12 patients. Grating acuity of at least 6/12 (20/40) was estimated in 12 patients. Residual vision can be measured in "difficult to examine" multiply handicapped patients with VEP and PL techniques.

Adolescent↗
PubMed2006

Evaluation of the accuracy of estimation retinoscopy.

BACKGROUND: Some children are unable to cooperate for retinoscopy because they object strongly to the placement of lenses close to their faces. For these children, it would be ideal to obtain an accurate estimate of refractive error without using lenses. Techniques of estimation retinoscopy include sliding the sleeve of the Copeland retinoscope downward or moving closer to the patient until neutrality is achieved. The purpose of this study was to evaluate the accuracy of estimation techniques by comparing results to standard retinoscopy with loose lenses in cooperative children. METHODS: A Copeland retinoscope was calibrated using a schematic eye and loose lenses. A scale was created adjacent to the sleeve of the retinoscope which allowed an estimate of refractive error based on the position of the top of the sleeve. Estimation retinoscopy followed by standard retinoscopy with loose lenses was done on 100 eyes of 50 children after cycloplegia. RESULTS: Estimation of spherical equivalent for myopia less than 4 D and hyperopia less than 2 D correlated strongly with results obtained by standard retinoscopy with loose lenses (r = 0.87). Estimation retinoscopy had a sensitivity of 88%, specificity of 67%, positive-predictive value of 58%, and negative-predictive value of 92% in the detection of amblyogenic refractive errors. CONCLUSIONS: Estimation retinoscopy has very good accuracy for low levels of myopia, hyperopia, and astigmatism. Techniques of estimation may be useful in excluding amblyogenic refractive errors, particularly in children who object to loose lenses held close to them.

Child↗