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PubMed1990

Refractive errors after cryotherapy in retinopathy of prematurity.

Because of acute retinopathy of prematurity 14 premature infants (900-1,630 g birth weight) were treated with cryocoagulation (10 children, both eyes; 4 only one eye) between 1976 and 1984 and were followed up until they were 2-7 years of age. The average refractive power of 20 eyes (those in which refraction could be determined) was -1.5 +/- 4.1 dptr. Twelve eyes (60.0%) were hyperopic (average: +1.3 +/- 0.4 dptr), and 8 eyes (40.0%) were myopic (average: -5.7 +/- 3.6 dptr). Three eyes in which cryocoagulation was done twice or three times because of a severe course developed pronounced myopia (greater than 7.0 dptr). When comparing both eyes of 4 children in whom cryotherapy had been carried out in only one eye, cryotherapy was found to have no influence on refractive errors (average anisometropia +0.4 +/- 0.4 dptr).

Birth Weight↗
PubMed1987

The relationship between tonic accommodation and refractive error.

It is now well established that accommodation adopts an intermediate resting position in the absence of visual stimulation. It also has been shown that this tonic position of accommodation exhibits considerable variation among individuals (ie, 0-4 D). Previous studies have been somewhat inconclusive as to whether these individual differences in tonic accommodation are related to the refractive properties of the eye. This study investigates the relationship between tonic accommodation and refractive error with particular reference to both the value and the time course of tonic accommodation. Sixty-two subjects were used for the study, with an age range of 19-25 yr. Subjects were placed into one of four refractive groups, after considering factors pertaining to the theories of refractive development. Darkroom measures of tonic accommodation were determined using the infrared objective autorefractor, Canon Autoref R-1. Significant differences were found among the four refractive groups, with corrected hyperopes having the highest dioptric value of tonic accommodation and corrected late-onset myopes having the lowest dioptric value. The significant difference found between early- and late-onset myopes is suggested as a possible reason for the inconclusive results of some previous studies. It also was found that the time taken to reach a stable tonic position of accommodation was much slower for the hyperopic group than for the other refractive groups. The results are discussed in the light of recent findings on accommodative hysteresis and with respect to a dual innervation to the ciliary muscle.

Accommodation, Ocular↗
PubMed1983

Mechanisms of accommodation and refractive error.

The classical or Helmholtz theory of accommodation has formed the basis of optometric practice for many years. This theory maintains that the ciliary muscle receives only parasympathetic innervation and that the position of rest in the emmetropic eye lies at optical infinity. The suggestion of a dual sympathetic/parasympathetic innervation to the ciliary muscle also dates from the last century. Recent studies indicate that the "dark focus" or resting point of accommodation lies at some intermediate distance and that the refractive state in the absence of an adequate stimulus represents the tonus position of the ciliary muscle for minimal autonomic innervation. This paper considers the possible role of a sympathetic innervation to the ciliary muscle in the development and correction of refractive errors.

Accommodation, Ocular↗
PubMed2002

Refractive error and visual outcome after cataract extraction.

PURPOSE: To determine the range of biometry prediction error of the postoperative refraction and the visual outcome after cataract surgery. SETTING: Postgraduate teaching hospital. METHODS: Refraction and visual outcomes were recorded prospectively for a consecutive case series of 1817 cataract procedures. Complete preoperative and postoperative data were available for 1676 eyes (92.4%). The paired mean error of the difference between the predicted and achieved refraction, the percentages falling within +/-0.50 diopter (D), +/-1.00 D, and +/-2.00 D, and the values that contained 99% of data points were then calculated. The number that achieved a final Snellen visual acuity of 6/12 was determined in all eyes and in eyes without preoperative ocular comorbidity. This analysis was repeated in 1265 eyes that received a single intraocular lens (IOL) design (C10UB/C11UB) after phacoemulsification through a clear corneal incision. RESULTS: The paired mean error of the difference between the predicted and achieved postoperative refraction in all eyes was -0.32 D +/- 1.05 (SD); 72.3% of eyes were within +/-1.00 D of the planned refraction, with bounds of 99% of observation of +2.92 D and -3.98 D. In the single IOL group, the paired mean error was -0.32 +/- 0.94 D; 74.2% of eyes fell within +/-1.00 D of the planned refraction, with bounds of 99% of observation of +2.54 D and -3.81 D. Axial length did not determine the magnitude of the biometry prediction error. At discharge from the service, 86.9% of all eyes and 95.4% of eyes without preoperative ocular comorbidity achieved a final corrected Snellen acuity of 6/12. CONCLUSION: These data provide benchmark information that can be used to monitor clinical practice.

Aged↗
PubMed2004

Correction of refractive error in the adult population of Bangladesh: meeting the unmet need.

PURPOSE: To assess the extent of uncorrected refractive error and associated factors in Bangladesh and to suggest ways in which this need can be met. METHODS: A nationally representative sample of 12,782 adults (>/= 30 years of age) was selected. Of them, 11,624 subjects underwent a demographic interview, visual acuity (logarithm of the minimum angle of resolution [logMAR]) measurement, automated refraction, and optic disc examination. Subjects with visual acuity less than 6/12 in either eye also had a corrected refraction measurement, cataract grading, and dilated retinal examination. RESULTS: Of the 11,624 subjects examined, 2,469 (22.1%) were myopes (less than -0.5 D) and 2,308 (20.6%) hyperopes (more than +0.5 D). The spectacle coverage percentage, calculated as [met need/(met need + unmet need) x 100%] was 25.2% and 40.5%, using 6/12 and 6/18 visual acuity cutoffs, respectively, and was higher in men and urban inhabitants. Older subjects and the literate and more highly educated were more likely to wear spectacles; however, most spectacle wearers (81%) had inadequate correction. Of the 1142 subjects who would benefit from spectacles, 827 (72.4%) would be suitable for off-the-shelf spectacles. Subjects without spectacles with less than 6/12 in the better eye (n = 835), would achieve 6/12 or better with correction (unmet need). Extrapolation to the national population yields an estimate that 1.5 million (6.7%) adult men and 1.8 million (9.2%) women have an unmet need for refractive correction. CONCLUSIONS: In Bangladesh, there is low spectacle coverage with a large unmet need. This survey identified risk groups, in particular women and those living in rural areas. This description of the availability of refractive services suggests areas for improvement (e.g., off-the-shelf spectacles) that may enable Bangladesh to achieve the goals of the World Health Organization's Vision 2020 initiative.

Adult↗
PubMed1988

Refraction and refractive errors in an elderly population.

The data for this paper were collected during a two-year study of the elderly in the market town of Melton Mowbray. The randomly selected subjects, aged 76 years of age and older, were found to be on average +1.33 D hypermetropic and the average cylinder power was 0.82 D. The mean refractive error was found to be +1.5 D with 0.5 negative cylinder at between 85 and 90 degrees. Of all the subjects, 30 per cent had significant anisometropia.

Aged↗
PubMed1977

Does refractive error change twice as fast as corneal power in orthokeratology?

We analyzed data from 4 orthokeratology studies of refractive error change (deltaRE) and keratometer-reading change (deltaK). Instead of the reported deltaRE/deltaK ratio of 2:1, we calculated from linear-regression analysis a ratio (slope) of 2:3. The ordinate intercept of the straight line fitted to the data (N = 181 eyes) indicates that when deltaK = 0, deltaRE = 0.72. The correlation between deltaK and deltaRE is poor (+0.63). Causes and interpretations of these results are discussed.

Contact Lenses↗
PubMed1992

Optic disc of the myopic eye: relationship between refractive errors and morphometric characteristics.

Because the optic disc in myopic eyes is different from a normal optic disc, there are many difficulties in examining the optic discs of myopic eyes. To study optic disc change due to myopia, we performed a morphometrical study of stereophotographs of 61 men, 109 eyes, who had no glaucoma history. The range of refractive error was from +0.75 diopter to -12.75 diopter, and all subjects had intraocular pressure below or equal to 21 mmHg. According to the increase in the myopic degree, the temporal slope of the disc cup was significantly decreased, but the ratio of the vertical disc diameter (VDD) to the horizontal disc diameter and the ratio of the width of peripapillary atrophy (PPA) to the VDD were significantly increased. The above results suggests that in high myopia the optic disc was tilted and the rim-cup border was indistinct and there are some problems in the estimation of the morphometric parameters. Also in evaluation of the PPA of myopic glaucoma patients, there may be some difficulty in deciding whether it is due to myopic change or glaucomatous damage.

Adolescent↗
PubMed1990

Refractive error, axial length, and height as a function of age in young myopes.

Classical studies suggest that growth of the eye as assessed by axial elongation ceases by 13 years of age. The subjects in these studies were mostly emmetropes. In contrast, the childhood progression of myopia continues to the middle to late teenage years. We collected cross-sectional data on refractive error, axial length, and height. Analysis of these data based on a linear regression model suggests that axial elongation continues later in myopes than the classical studies suggest. The age of cessation of axial elongation in myopes was earlier in females than in males. For both sexes, the ages of axial elongation cessation in myopes were similar to the ages of cessation of increases in height.

Adolescent↗
PubMed2005

Accommodation functions: co-dependency and relationship to refractive error.

We assessed the extent to which different accommodative functions are correlated and whether accommodative functions predict the refractive error or the progression of myopia over a 12 month period in 64 young adults (30 myopes and 34 non-myopes). The functions were: amplitude of accommodation; monocular and binocular accommodative facility (6 m and 40 cm); monocular and binocular accommodative response to target distance; AC/A and CA/C ratios, tonic accommodation (dark focus and pinhole), accommodative hysteresis, and nearwork-induced transient myopia. Within groups of related accommodative functions (such as facility measures or open-loop measures) measurements on individuals were generally significantly correlated, however correlations between functions from different groups were generally not significant. Although accommodative amplitude and pinhole (open loop) accommodation were significantly different in myopes than in non-myopes, these functions were unrelated to myopia progression. Facility of accommodation and accommodative lag was independent predictors of myopia progression.

Accommodation, Ocular↗
PubMed1998

Cycloplegic refractive errors in children: comparison of a standard and a hand-held refractor.

The present study compares the refraction of normal children and young adults measured with a standard refractor and a hand-held refractor. Refractive errors were estimated for each refractor under cycloplegia: sphere, cylinder and cylinder axis were compared. No significant difference was found between the two methods. We performed this study before starting a screening campaign in preschool children to evaluate if the pediatrician and paramedical staff may rely on the hand-held refractors.

Journal Article↗
PubMed1994

6-Hydroxy dopamine does not affect lens-induced refractive errors but suppresses deprivation myopia.

Degradation of the retinal image by translucent occluders during postnatal development induces axial myopia in chickens, tree shrews and monkeys. Local visual deprivation produces myopia even in local regions of the eye and neither accommodation nor intact connection between the eye and the brain are necessary. Therefore, it is an important question whether a similar local-retinal pathway translating visual information into growth or stretch signals to the underlying sclera is acting to emmetropize the growing eye. It is not known until now whether occluder deprivation triggers similar eye growth (or scleral stretch) mechanisms that are also responsible for visual guidance of normal refractive development. We here report that, in chickens, 6-hydroxy dopamine suppresses deprivation-induced myopia but has no effect on the magnitude of changes in axial eye elongation that are induced by spectacle lenses. The result suggests that, in chickens with normal accommodation, two pharmacologically different feedback loops may be responsible for deprivation myopia and lens-induced refractive errors.

Animals↗
PubMed1983

Choroidal folds and refractive errors associated with orbital tumors. An analysis.

Twenty patients with unilateral exophthalmos secondary to orbital tumors underwent fundus photography; 16 underwent fluorescein angiography. Choroidal folds were found in 15 eyes. The location of each tumor with respect to the globe was determined by computed tomography. In addition, most patients underwent B-scan ultrasonography and surgical exploratory procedures. Choroidal folds were more common in patients with greater amounts of exophthalmos and with anteriorly located tumors. Moreover, the pattern of choroidal folds generally reflected the location of the tumor within the orbit. Comparison with the uninvolved fellow eyes showed that preoperative refractive errors were usually shifted toward hyperopia with intraconal tumors, whereas extraconal tumors were typically associated with higher astigmatic errors on the involved side.

Diagnosis, Differential↗
PubMed2002

Peripheral refractive errors in myopic, emmetropic, and hyperopic young subjects.

To gain more insight into the relationship between foveal and peripheral refractive errors in humans, spheres, cylinders, and their axes were binocularly measured across the visual field in myopic, emmetropic, and hyperopic groups of young subjects. Both automated infrared photorefraction (the "PowerRefractor"; www. plusoptix.de) and a double-pass technique were used because the PowerRefractor provided extensive data from the central 44 deg of the visual field in a very convenient and fast way. Two-dimensional maps for the average cross cylinders and spherical equivalents, as well as for the axes of the power meridians of the cylinders, were created. A small amount of lower-field myopia was detected with a significant vertical gradient in spherical equivalents. In the central visual field there was little difference among the three refractive groups. The established double-pass technique provided complementary data also from the far periphery. At 45 deg eccentricity the double-pass technique revealed relatively more hyperopic spherical equivalents in myopic subjects than in emmetropic subjects [+/-2.73 +/- 2.85 D relative to the fovea, p < 0.01 (+/- standard deviation)] and more myopic spherical equivalents in hyperopic subjects (-3.84 +/- 2.86 D relative to the fovea, p < 0.01). Owing to the pronounced peripheral astigmatism, spherical equivalents (refractions with respect to the plane of the circle of least confusion) became myopic relative to the fovea in all three groups. The finding of general peripheral myopia was unexpected. Its possible roles in foveal refractive development are discussed.

Adult↗
PubMed1991

Normalisation of refractive error after steroid injection for adnexal haemangiomas.

A longitudinal study of 27 patients with infantile haemangiomas is reported. It confirmed the efficacy of local steroid injection as a method of treatment; 81.5% of patients showed a marked improvement, with the lesion reducing to 25% or less of its original size. Involution was most marked in the first two weeks but continued for up to four months after injection. Amblyopia was present in 43% of children and was usually the result of induced refractive error rather than obstruction of the visual axis or strabismus. Anisometropia was found in 68% of children, with a high incidence of asymmetric astigmatism on the side of the haemangioma. Following local steroid injection a marked reduction in astigmatism was noted in 53.8% of children, a lesser reduction in 15.4%, and no reduction in 30.8%. Successful treatment of the haemangioma, therefore, may not remove the risk of amblyopia, and regular refraction and visual assessment remain mandatory.

Adolescent↗