Corneal Topography Raw Data Classification Using a Convolutional Neural Network.

PURPOSE: We investigated the efficiency of a convolutional neural network applied to corneal topography raw data to classify examinations of 3 categories: normal, keratoconus (KC), and history of refractive surgery (RS). DESIGN: Retrospective machine-learning experimental study. METHODS: A total of 3,000 Orbscan examinations (1,000 of each class) of different patients of our institution were selected for model training and validation. One hundred examinations of each class were randomly assigned to the test set. For each examination, the raw numerical data from "elevation against the anterior best fit sphere (BFS)," "elevation against the posterior BFS" "axial anterior curvature," and "pachymetry" maps were used. Each map was a square matrix of 2,500 values. The 4 maps were stacked and used as if they were 4 channels of a single image.A convolutional neural network was built and trained on the training set. Classification accuracy and class wise sensitivity and specificity were calculated for the validation set. RESULTS: Overall classification accuracy of the validation set (n = 300) was 99.3% (98.3%-100%). Sensitivity and specificity were, respectively, 100% and 100% for KC, 100% and 99% (94.9%-100%) for normal examinations, and 98% (97.4%-100%) and 100% for RS examinations. CONCLUSION: Using combined corneal topography raw data with a convolutional neural network is an effective way to classify examinations and probably the most thorough way to automatically analyze corneal topography. It should be considered for other routine tasks performed on corneal topography, such as refractive surgery screening.

Refractive errors in children and adolescents in Bucaramanga (Colombia).

PURPOSE: The aim of this study was to establish the frequency of refractive errors in children and adolescents aged between 8 and 17 years old, living in the metropolitan area of Bucaramanga (Colombia). METHODS: This study was a secondary analysis of two descriptive cross-sectional studies that applied sociodemographic surveys and assessed visual acuity and refraction. Ametropias were classified as myopic errors, hyperopic errors, and mixed astigmatism. Eyes were considered emmetropic if none of these classifications were made. The data were collated using free software and analyzed with STATA/IC 11.2. RESULTS: One thousand two hundred twenty-eight individuals were included in this study. Girls showed a higher rate of ametropia than boys. Hyperopic refractive errors were present in 23.1% of the subjects, and myopic errors in 11.2%. Only 0.2% of the eyes had high myopia (≤-6.00 D). Mixed astigmatism and anisometropia were uncommon, and myopia frequency increased with age. There were statistically significant steeper keratometric readings in myopic compared to hyperopic eyes. CONCLUSIONS: The frequency of refractive errors that we found of 36.7% is moderate compared to the global data. The rates and parameters statistically differed by sex and age groups. Our findings are useful for establishing refractive error rate benchmarks in low-middle-income countries and as a baseline for following their variation by sociodemographic factors.

Refractive errors in children and adolescents in Bucaramanga (Colombia) / Erros refrativos em crianças e adolescents em Bucaramanga (Colombia)

ABSTRACT Purpose: The aim of this study was to establish the frequency of refractive errors in children and adolescents aged between 8 and 17 years old, living in the metropolitan area of Bucaramanga (Colombia). Methods: This study was a secondary analysis of two descriptive cross-sectional studies that applied sociodemographic surveys and assessed visual acuity and refraction. Ametropias were classified as myopic errors, hyperopic errors, and mixed astigmatism. Eyes were considered emmetropic if none of these classifications were made. The data were collated using free software and analyzed with STATA/IC 11.2. Results: One thousand two hundred twenty-eight individuals were included in this study. Girls showed a higher rate of ametropia than boys. Hyperopic refractive errors were present in 23.1% of the subjects, and myopic errors in 11.2%. Only 0.2% of the eyes had high myopia (≤-6.00 D). Mixed astigmatism and anisometropia were uncommon, and myopia frequency increased with age. There were statistically significant steeper keratometric readings in myopic compared to hyperopic eyes. Conclusions: The frequency of refractive errors that we found of 36.7% is moderate compared to the global data. The rates and parameters statistically differed by sex and age groups. Our findings are useful for establishing refractive error rate benchmarks in low-middle-income countries and as a baseline for following their variation by sociodemographic factors.

RESUMO Objetivo: O objetivo deste estudo foi estabelecer a frequência de erros refrativos em crianças e adolescentes com idade entre 8 e 17 anos, residentes na região metropolitana de Bucaramanga (Colômbia). Métodos: Este estudo foi uma análise secundária de dois estudos descritivos transversais que aplicaram levantamentos sociodemográficos e avaliaram a acuidade e a refração visuais. As ametropias foram classificadas como erros miopicos, erros hipermetrópicos e astigmatismo misto. Os olhos eram considerados emétropes se nenhuma dessas classificações fosse feita. Os dados foram coletados usando software livre e analisados com STATA/IC 11.2. Resultados: Mil e duzentos e vinte e oito indivíduos foram incluídos neste estudo. As meninas mostraram uma maior taxa de ametropia do que os meninos. Erros refrativos hipermetrópicos estavam presentes em 23,1% dos indivíduos e erros miópicos em 11,2%. Apenas 0,2% dos olhos apresentavam miopia alta (≤-6,00 D). O astigmatismo misto e a anisometropia eram incomuns e a frequência de miopia aumentava com a idade. Houve leituras queratométricas mais acentuadas estatisticamente significativas em míopes em comparação com os olhos hipermétropes. Conclusões: A frequência de erros de refração que encontramos em 36,7% é moderada em comparação com os dados globais. As taxas e os parâmetros diferiram estatisticamente por sexo e grupos etários. Nossas descobertas são úteis para estabelecer padrões de referência de erro de refração em países de baixa renda média e como base para seguir sua variação por fatores sociodemográficos.

Comparison of noncycloplegic and cycloplegic autorefraction in categorizing refractive error data in children.

PURPOSE: To systematically analyse the differences between cycloplegic and noncycloplegic refractive errors (RE) in children and to determine if the predictive value of noncycloplegic RE in categorizing RE can be improved. METHODS: Random cluster sampling was used to select 6825 children aged 4-15 years. Autorefraction was performed under both noncycloplegic and cycloplegic (induced with 1% cyclopentolate drops) conditions. Paired differences between noncycloplegic and cycloplegic spherical equivalent (SE) RE were determined. A general linear model was developed to determine whether cycloplegic SE can be predicted using noncycloplegic SE, age and uncorrected visual acuity (UCVA). RESULTS: Compared to cycloplegia, noncycloplegia resulted in a more myopic SE (paired difference: -0.63 ± 0.65D, 95% CI: -0.612 to -0.65D, 6017 eligible right eyes) with greater differences observed in younger participants and in eyes with more hyperopic RE and smaller AL. Using raw noncycloplegic data resulted in only 61% of the eyes being correctly classified as myopic, emmetropic or hyperopic. Using age and uncorrected VA in the model, the association improved and 77% of the eyes were classified correctly. However, predicted cycloplegic SE continued to show large residual errors for low myopic to hyperopic RE. Applying the model to only those eyes with uncorrected VA <6/6 resulted in an improvement (R2  = 0. 93), with 80% of the eyes correctly classified. A higher VA cut-off (i.e., ≤6/18) resulted in 97.5% of eyes classified correctly. CONCLUSION: Noncycloplegic assessment of RE in children overestimates myopia and results in a high error rate for emmetropic and hyperopic RE. Adjusting for age and applying uncorrected VA cut-offs to noncycloplegic assessments improves detection of myopic RE and may help in identifying myopic RE in situations where cycloplegia is not available but does not help in identifying the magnitude of refractive error and therefore is of limited value.

Caracterización de las ametropías atendidas en Consulta de Cirugía Refractiva del Centro Oftalmológico de Holguín / Characterization of Ametropia Present in Patients Attended in Refractive Surgery Consultation of Ophthalmological Center of Holguín

Introducción: las ametropías constituyen un motivo de consulta frecuente en Oftalmología.Objetivo: caracterizar las ametropías presentes en los pacientes atendidos en la Consulta de Cirugía Refractiva del Centro Oftalmológico de Holguín.Métodos: se realizó estudio descriptivo transversal con una muestra no probabilística de 112 pacientes con criterio quirúrgico, evaluados en el período de enero-diciembre de 2013. Las variables fueron: ametropía, corrección esférica, corrección cilíndrica, lateralidad, queratometría, longitud axial, agudeza visual no corregida y mejor agudeza visual corregida.Resultados: se encontró astigmatismo en el 98,22 % de los pacientes, de ellos el 93,63 % con astigmatismo miópico compuesto. La esfera y el cilindro modular medios fueron de 5,57 y 1,75 dioptrías respectivamente. El astigmatismo fue bilateral en el 90,18 % de los casos y a favor de la regla en el 69,09 %. La queratometría media fue de 43,73 dioptrías y la longitud axial media de 25,46 mm. La agudeza visual sin corrección promedio fue 0,05 mientras que la mejor agudeza visual corregida promedio fue 0,98.Conclusiones: La ametropía predominante fue el astigmatismo miópico compuesto, bilateral, de grado moderado y a favor de la regla. Predominaron los defectos con doble componente: axial y de curvatura. Existió correspondencia entre los métodos objetivos y la refracción subjetiva en la mayoría de los casos. La presencia de anisometropías y de ambliopías refractivas fue baja. Se encontró un gran número de pacientes con hipercorrección esférica a expensas del cilindro y por tanto se identificaron defectos astigmáticos no corregidos hasta ese momento.(AU)

Introduction: ametropia is a frequent cause of consultation in Ophthalmology Service.Purpose: to characterize ametropia present in patients attended in refractive surgery consultation at the Ophthalmological Center of Holguín.Methods: a descriptive and cross-sectional study was conducted with a non-probabilistic sample of 112 patients that fulfilled surgical criteria from the ones assessed from January to December 2013. The analyzed variables were: ametropia, spherical correction, cylindrical correction, laterality, keratometry, axial length, non-corrected visual acuity and best visual corrected acuity.Results: astigmatism was found in 98.22 % of patients, and its compound-myopic type in 93.63 % among them, with an average sphere of 5.57 diopters and an average modular cylinder of 1.75 diopters. The astigmatism was bilateral in 90.18 % of patients and with-the-rule in 69.09 % of them. The mean keratometry found was 43.73 diopters and the mean axial length was 25.46 mm. The average uncorrected visual acuity was 0.05 whereas the average best corrected visual acuity was 0.98.Conclusions: moderate-grade miopic astigmatism predominated as refractive defects and it was most frequently bilateral. With-the-rule astigmatisms and combined ametropia (refractive and axial) were predominant. There was correspondence between subjective and objective refraction in most of the patients. The presence of anisometropia and refractive amblyopia were low. A large amount of patients with spherical overcorrection at cost of cylinder were found and therefore uncorrected astigmatisms were identified.(AU)

Accuracy of noncycloplegic retinoscopy, retinomax autorefractor, and SureSight vision screener for detecting significant refractive errors.

PURPOSE: To evaluate, by receiver operating characteristic (ROC) analysis, the ability of noncycloplegic retinoscopy (NCR), Retinomax Autorefractor (Retinomax), and SureSight Vision Screener (SureSight) to detect significant refractive errors (RE) among preschoolers. METHODS: Refraction results of eye care professionals using NCR, Retinomax, and SureSight (n = 2588) and of nurse and lay screeners using Retinomax and SureSight (n = 1452) were compared with masked cycloplegic retinoscopy results. Significant RE was defined as hyperopia greater than +3.25 diopters (D), myopia greater than 2.00 D, astigmatism greater than 1.50 D, and anisometropia greater than 1.00 D interocular difference in hyperopia, greater than 3.00 D interocular difference in myopia, or greater than 1.50 D interocular difference in astigmatism. The ability of each screening test to identify presence, type, and/or severity of significant RE was summarized by the area under the ROC curve (AUC) and calculated from weighted logistic regression models. RESULTS: For detection of each type of significant RE, AUC of each test was high; AUC was better for detecting the most severe levels of RE than for all REs considered important to detect (AUC 0.97-1.00 vs. 0.92-0.93). The area under the curve of each screening test was high for myopia (AUC 0.97-0.99). Noncycloplegic retinoscopy and Retinomax performed better than SureSight for hyperopia (AUC 0.92-0.99 and 0.90-0.98 vs. 0.85-0.94, P ≤ 0.02), Retinomax performed better than NCR for astigmatism greater than 1.50 D (AUC 0.95 vs. 0.90, P = 0.01), and SureSight performed better than Retinomax for anisometropia (AUC 0.85-1.00 vs. 0.76-0.96, P ≤ 0.07). Performance was similar for nurse and lay screeners in detecting any significant RE (AUC 0.92-1.00 vs. 0.92-0.99). CONCLUSIONS: Each test had a very high discriminatory power for detecting children with any significant RE.

Peripheral refraction profiles in subjects with low foveal refractive errors.

PURPOSE: To study the variability of peripheral refraction in a population of 43 subjects with low foveal refractive errors. METHODS: A scan of the refractive error in the vertical pupil meridian of the right eye of 43 subjects (age range, 18 to 80 years, foveal spherical equivalent, < ± 2.5 diopter) over the central ± 45° of the visual field was performed using a recently developed angular scanning photorefractor. Refraction profiles across the visual field were fitted with four different models: (1) "flat model" (refractions about constant across the visual field), (2) "parabolic model" (refractions follow about a parabolic function), (3) "bi-linear model" (linear change of refractions with eccentricity from the fovea to the periphery), and (4) "box model" ("flat" central area with a linear change in refraction from a certain peripheral angle). Based on the minimal residuals of each fit, the subjects were classified into one of the four models. RESULTS: The "box model" accurately described the peripheral refractions in about 50% of the subjects. Peripheral refractions in six subjects were better characterized by a "linear model," in eight subjects by a "flat model," and in eight by the "parabolic model." Even after assignment to one of the models, the variability remained strikingly large, ranging from -0.75 to 6 diopter in the temporal retina at 45° eccentricity. CONCLUSIONS: The most common peripheral refraction profile (observed in nearly 50% of our population) was best described by the "box model." The high variability among subjects may limit attempts to reduce myopia progression with a uniform lens design and may rather call for a customized approach.

Profile of refractive errors in cerebral palsy: impact of severity of motor impairment (GMFCS) and CP subtype on refractive outcome.

PURPOSE: To describe refractive status in children and young adults with cerebral palsy (CP) and relate refractive error to standardized measures of type and severity of CP impairment and to ocular dimensions. METHODS: A population-based sample of 118 participants aged 4 to 23 years with CP (mean 11.64 +/- 4.06) and an age-appropriate control group (n = 128; age, 4-16 years; mean, 9.33 +/- 3.52) were recruited. Motor impairment was described with the Gross Motor Function Classification Scale (GMFCS), and subtype was allocated with the Surveillance of Cerebral Palsy in Europe (SCPE). Measures of refractive error were obtained from all participants and ocular biometry from a subgroup with CP. RESULTS: A significantly higher prevalence and magnitude of refractive error was found in the CP group compared to the control group. Axial length and spherical refractive error were strongly related. This relation did not improve with inclusion of corneal data. There was no relation between the presence or magnitude of spherical refractive errors in CP and the level of motor impairment, intellectual impairment, or the presence of communication difficulties. Higher spherical refractive errors were significantly associated with the nonspastic CP subtype. The presence and magnitude of astigmatism were greater when intellectual impairment was more severe, and astigmatic errors were explained by corneal dimensions. Conclusions. High refractive errors are common in CP, pointing to impairment of the emmetropization process. Biometric data support this CONCLUSION: In contrast to other functional vision measures, spherical refractive error is unrelated to CP severity, but those with nonspastic CP tend to demonstrate the most extreme errors in refraction.

Measuring refraction in adults in epidemiological studies.

OBJECTIVE: To compare refraction measured before and after pharmacologic cycloplegia. METHODS: This study used preliminary data from the Beaver Dam Offspring Study, which includes adult children of participants in the population-based Epidemiology of Hearing Loss Study of older adults living in Beaver Dam, Wisconsin. Data were available for 5018 eyes of 2529 participants. Refraction was defined by the spherical equivalent (SE), using autorefractor readings. Differences were calculated as the SE after drops were administered minus the SE before drops were administered. Myopia was defined as SE of -1 diopter (D) or less; emmetropia, as SE more than -1 D and less than 1 D; and hyperopia, as SE of 1 D or more. RESULTS: The mean age was 48 years (range, 22-84 years). The mean difference in SE between measurements before and after cycloplegia was 0.29 D (95% confidence interval, 0.28-0.31). The difference decreased with age and varied by refractive status for participants younger than 50 years, with the largest differences observed among young persons with hyperopic refractive errors. Across all age groups, agreement on classifications of refraction was high (84%-92%). CONCLUSIONS: Overall, clinically inconsequential differences were observed between SEs before and after pharmacologic cycloplegia, suggesting that cycloplegia may not be necessary in epidemiological studies of refraction in adults.

[Refraction and accommodation].

The main purpose of ophthalmology is to improve the quality of vision by the recovery of visual function. Visual acuity, among the visual functions, is the most important factor. Decreased far vision is caused mainly by refractive errors, while decreased near vision is caused by accommodative insufficiency, especially presbyopia. REFRACTIVE ERRORS: The development of myopia may be influenced by both polygenic and environmental factors. Investigation of the mechanism of myopia has progressed based on the experimental animal models of myopia. The conventional treatments for refractive errors is spectacles or contact lenses, and new treatment includes phakic IOL, orthokeratology, and refractive surgery. There are also newly designed types of equipment to assess refraction and refractive elements. ACCOMMODATIVE INSUFFICIENCY: Presbyopia is mainly corrected using multifocal or progressive power spectacle lenses. Nowadays, bifocal and multifocal contact lenses and sometimes surgical treatment are used for presbyopia. Equipment for asthenopia has also been developed.

[Infant ametropias and their evolutions (myopia, hyperopia, astigmatism)]. / Ametropies de l'enfant et leurs évolutions (myopie, hypermétropie, astigmatisme).

Infant ametropias are defined as the whole optic caracteristics of the eyeball which do not allow a clear vision whithout functional disorder. As the sensorial maturity is only achieved at 4 to 5 years, the limits of ametropias are variable before that age. The majority of ametropias is constituted as early as 9 months and may be detected by a refractive examination under cycloplegia. This situation is especially true for hyperopia and astigmatism. The more important are initial ametropias the more unchanged they remain. At 9 months, 1 infant out of 5 present a non-physiological refraction. From 4 to 5 years, 1 child out of 4 needs a refractive correction. Significant myopias are uncommon in infants. They generally appear between 7 and 12 years.

Prevalence of refractive error in mentally retarded students of Kathmandu Valley.

Mental retardation also known as 'mentally handicap' means a delay or insufficient development of mental capacities. The prevalence of mental retardation in Nepal is 4.1%. Vision being the best sense for their education and daily activities, a cross-sectional and descriptive study was conducted to find out the refractive error among the students in the schools for mentally retarded people. A total of 134 clinically diagnosed cases of mentally retarded students from three different schools of Kathmandu Valley were examined. Distance visual acuity was taken with the help of Cat Ford Vision Drum, SG chart and Kay Picture Test method but first preference was given to SG chart. Cyclo-retinoscopy and fundus examination under mydriasis were done in all the cases. Examination revealed that more than half of the examined had one or more ocular disorders with refractive error being the most common type of ocular morbidity followed by ocular motility disorders. Refractive errors were found in 34.4% in which the most common type of refractive error was simple hypermetropia. In conclusion refractive error was seen commonly among mentally retarded people of Kathmandu Valley.

Prevalence of amblyopia in ametropias in a clinical set-up.

OBJECTIVE: To find out prevalence of amblyopia in ametropias in a clinical set-up. MATERIALS AND METHODS: In this retrospective clinical study children from 4-5 years age group to the young adults who attended the eye clinic in one year period were included after taking history, VA test by Snellen's Vision Chart, cycloplegic refraction by streak retinoscope in children and wet or dry retinospcopy in young adults; and a thorough anterior and posterior segment eye examinations by slit lamp biomicroscope and ophthalmoscope to exclude structural abnormality of the eye or the posterior visual pathway defects. A total of 970 eye patients having diminution of vision with ametropias were identified and patients having reduction of visual acuity of greater than two lines between the eyes or an absolute reduction in acuity below 6/9 either eye in snellen's vision chart which cannot be corrected by refraction were enrolled to find out prevalence of amblyopia. RESULTS: Out of 970 ametropic eye patients amblyopia was present in 56 patients (5.97%) with anisometropias and high bilateral ametropias. The prevalence of amblyopia according to types of ametropias are: hyperopia 6 (10.71%), myopia 2 (3.57%), myopic astigmatism 31 (55.36%), hyperopic astigmatism 11 (19.64%) and mixed astigmatism 6 (10.71%). Sex distribution of amblyopia is male 32 (57.14%) and female 24 (42.86%). Laterality of amblyopia shows: monocular 40 (71.43%) and binocular 16 (28.57%). CONCLUSION: Out of 970 ametropic eye patients a total of 56 (5.97%) patients have amblyopia. A preschool and school screening program in children in critical period of development of amblyopia must be conducted to find out the ametropias and amblyopia in time; and treat them earlier, by optical correction and amblyopia therapy, effectively and adequately.

[Distribution and enantiomorphism of higher-order ocular optical aberrations]. / Etude de la distribution et de l'énantiomorphisme des aberrations optiques oculaires de haut degré.

PURPOSE: To characterize and investigate the higher-order optical aberrations (HOAs) and their distribution and symmetry between both eyes (enantiomorphism). PATIENTS AND METHODS: Wave-front measurements were taken using Hartmann-Shack aberrometry and Zernike polynomial terms reconstruction of the total ocular wave front. Optical aberrations were quantitatively analyzed using the RMS (root mean square) Zernike coefficient term value. Symmetry between both eyes was assessed for each aberration according to two criteria: the RMS coefficient value and aberration magnitude. RESULTS: Sixty patients were included in the study. The HOAs presenting the highest magnitude were fourth-order spherical aberration (Z40; M=0.3038 microm), primary coma (Z31; magnitude M=0.2285 microm) and trefoil (Z33; M=0.1870 microm). A significant mirror symmetry between both eyes was present for high-order aberration orientations. Considering the magnitude of each aberration, symmetry was present in seven of eight aberrations (all but primary coma). HOAs were higher for ametropes than emmetropes. The hyperoptic eyes had more spherical aberrations than myopic and emmetropic eyes. CONCLUSION: Symmetry between the right and left eye is a less common characteristic of HOAs. The difference in the mean age of the studied population may account for the differences in the total high-order and spherical aberration levels found in our study.

[The practicality of wavefront correction in ophthalmology]. / Die Anwendbarkeit der Wellenfrontkorrektur in der Augenheilkunde.

BACKGROUND: "Wavefront correction" has become an often used concept in refractive surgery, even though it is not always uniquely defined. Clinical results, however, are lagging behind the original expectations. METHOD: The physical items wavefront error, light ray, ray tracing and refraction error first have to be well defined, including demonstration of the applicability of the underlying model assumptions. In our simulations optical errors of the eye are expressed in three different ways: two-dimensional refraction error maps, error maps of optical path lengths, and blurred images on the retina. RESULTS: Optical errors are completely correctable only at the locations where they originally occur, i. e., corneal errors at the cornea, lens errors in the lens. Correction at another localization always introduces new errors. Other than in astronomical telescopes, the correction of optical path length errors in the human eye is already limited by short time-scale fluctuations of the relevant parameters which are two orders of magnitude beyond the tolerable error limits. Approximation of the optical path length error by a series expansion (e. g., Zernike polynomials) can induce additional errors. CONCLUSION: The worse the optical properties of an eye are, the less is the wavefront approach applicable for correction.

Refractive errors among students occupying rooms lighted with incandescent or fluorescent lamps.

The purpose of the study was to determine whether the development of refractive errors could be associated with exposure to light emitted by incandescent or fluorescent lamps. 3636 students were examined (1638 boys and 1998 girls, aged 6-18 years, mean age 12.1, SD 3.4). The examination included retinoscopy with cycloplegia. Myopia was defined as refractive error < or = -0.5 D, hyperopia as refractive error > or = +1.5 D, astigmatism as refractive error > 0.5 DC. Anisometropia was diagnosed when the difference in the refraction of both eyes was > 1.0 D. The children and their parents completed a questionnaire on exposure to light at home. Data were analyzed statistically with the chi2 test. P values of less than 0.05 were considered statistically significant. It was found that the use of fluorescent lamps was associated with an increase in the occurrence of hyperopia (P < 0.01). There was no association between sleeping with the light turned on and prevalence of refractive errors.

[The analysis of refractive error in children and adolescents from 6-15 years of age based on 1000 examinations in two major Polish regions]. / Ocena refrakcji u dzieci i mlodziezy w wieku od 6 do 15 lat na podstawie badan 10000 osób, przeprowadzonych w województwach mazowieckim i dolnoslaskim.

PURPOSE: The aim of this study is to present the results of screening examinations of refractive errors, taken on 1002 of school children ranging from 6 to 15 years of age. MATERIAL AND METHODS: As the result of Internet screening visual acuity and color perception tests named "I can see..." in 10,021 children from randomly chosen schools in Poland in the year 2002, the group of 1002 children was chosen. In this group, the subjective and objective refractive error examination was taken as well as the visual acuity test, color perception with the use of Ishihara tables and full ophthalmologic examination. RESULTS: Average visual acuity was RE: 0.72 (SD +/- 0.31) and LE: 0.72 (SD +/- 0.31). The prevalence of emmetropia was 34%. In the examined group myopia in 17%, hyperopia in 20%, astigmatism in 5.5% of children was found, and in 24.5% of patients complex errors occur such as myopic and hyperopic astigmatism.

Distribution of axial, corneal, and combined ametropia in a refractive surgery unit.

PURPOSE: To group eyes in our refractive surgery unit on the basis of the origin of their ametropia and to assess the percentage of eyes in the different groups. METHODS: Refractive parameters and the axial eye length (AL) of 131 eyes of 131 persons with different refraction were measured. The eyes were initially classified into five groups on the basis of the grade of their ametropia: hypermetropic (> +0.5 D, n = 35), emmetropic (between +/- 0.5 D, n = 24), low myopic (between -0.75 and -4.0 D, n = 24), medium myopic (between -4.25 and -8.0 D, n = 24), and high myopic (over -8.0 D, n = 24). Then a classification scheme was made to group the origin of the ametropia on the basis of AL and corneal refractive power. RESULTS: In the hypermetropic group pure corneal origin was found in 8.6%, pure axial origin in 62.8%, and combined origin in 28.6% of the eyes. In the low myopic group these values were 20.9%, 29.2%, and 45.8%, respectively. In the medium and high myopic groups no pure corneal myopia was found, while axial myopia was found in 16.7% and combined myopia in 83.3% of the eyes. CONCLUSIONS: With the help of the classification scheme, an objective decision could be made as to whether the ametropia of a particular eye had axial, corneal, or mixed origin. The most interesting result was that in 83% of medium and high myopic eyes not only AL but also corneal refractive power contributed to the refractive error instead of the eyes being purely axially myopic.