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Effect of recipient-donor trephine size disparity on refractive error in keratoconus.
A retrospective study was performed to evaluate the effect of recipient-donor trephine disparity on refractive error and corneal curvature post-suture removal in keratoconus. A double running suture technique was used and donor corneas were trephined from the endothelial side. When keratoconus patients with 0.25-mm larger donor than recipient trephines were compared with keratoconus patients with the same size recipient and donor trephines, a statistically significant increase in the mean keratometer value (45.4 and 43.8 diopters [D], respectively; P = 0.03) and increase in myopic spherical equivalent (-3.5 and -1.8 D, respectively; P = 0.03) was found. When keratoconus patients were compared with phakic Fuchs' dystrophy patients (both groups had 0.25-mm oversize donor trephines), the keratoconus group had a statistically significantly higher myopic spherical equivalent (-3.5 and -1.4 D, respectively; P = 0.03) despite only a 0.7-D difference in mean keratometer value which was not statistically significant (45.4 and 44.7 D, respectively). This study supports the hypothesis that the degree of post-penetrating keratoplasty myopia in patients with keratoconus can be decreased by reducing recipient-donor trephine disparity.
Prevalence of amblyopia and associated refractive errors in an adult population in Victoria, Australia.
The study aimed to describe the prevalence of amblyopia and associated refractive errors among an adult Australian population. The Visual Impairment Project (VIP) is a population-based study of age-related eye disease in the state of Victoria, Australia. Data were collected through standardised interviews and orthoptic and ophthalmic dilated examinations. Amblyopia was defined as best-corrected visual acuity of 6/9 or worse in the absence of any pathological cause. The participants were 3,265 urban residents and 1,456 rural residents of the VIP ranging in age from 40-92 years (mean = 59 years; 53% female). The prevalence of unilateral amblyopia was 3.06% (95% C.I. 2.59, 3.53). Amblyopia was not found to be statistically different by age group (p=0.096), gender (p=0.675), or place of birth (p=0.14). Anisometropia was statistically more common (p<0.001) in amblyopic cases (51.1%) compared to the normal population (9.7%), and 54% of amblyopic eyes had visual acuity of worse than 6/12. Amblyopia is a significant cause of unilateral reduced visual acuity in a population aged 40 years and older. Anisometropia was more prevalent and the degree of anisometropia was greater in the amblyopic group compared with the normal population. Oblique astigmatism was more prevalent in the amblyopic group compared with the normal population.
Refractive-error changes in kitten eyes produced by chronic on-channel blockade.
The dependence of the emmetropization process on retinal ON-channel activity was examined in developing kittens by making regular intravitreal injections of D,L-2-amino-4-phosphonobutyric acid (APB). In comparison to sham-injected control eyes, the APB-treated eyes had shorter axial lengths and were more hyperopic. Since chronic atropinization did not alter the development of the APB-induced hyperopia, these anomalous refractive errors are not the result of altered accommodative function. The axial hyperopia observed in the APB-treated eyes indicates that the mechanisms responsible for normal axial elongation are dependent to some extent on ON-channel activity and that, even in the presence of a clear retinal image, OFF-channel activity, by itself, is not sufficient to regulate the normal emmetropization process.
The refractive error after implantation of a posterior chamber intraocular lens. The accuracy of IOL power calculation in a hospital practice.
The study included 188 patients, in which a posterior chamber intraocular lens was implanted after extracapsular cataract extraction. After modifications of the intraocular lens constants (SRK formula and SRK II formula) and correction of the axial length measurements (Colenbrander-Hoffer formula) had been made, the mean differences between the actual postoperative spherical equivalent and that predicted by the three formulas were -0.23D, -0.22D and -0.46D, respectively. More than +/-1.0D deviation from the predicted postoperative refraction occurred in about one-third of the cases. Inter-observed discrepancy regarding the accuracy of the preoperative measurement of the ocular axis length is suggested to be the main cause of unpredicted postoperative refractive errors.
Power vectors: an application of Fourier analysis to the description and statistical analysis of refractive error.
The description of sphero-cylinder lenses is approached from the viewpoint of Fourier analysis of the power profile. It is shown that the familiar sine-squared law leads naturally to a Fourier series representation with exactly three Fourier coefficients, representing the natural parameters of a thin lens. The constant term corresponds to the mean spherical equivalent (MSE) power, whereas the amplitude and phase of the harmonic correspond to the power and axis of a Jackson cross-cylinder (JCC) lens, respectively. Expressing the Fourier series in rectangular form leads to the representation of an arbitrary sphero-cylinder lens as the sum of a spherical lens and two cross-cylinders, one at axis 0 degree and the other at axis 45 degrees. The power of these three component lenses may be interpreted as (x,y,z) coordinates of a vector representation of the power profile. Advantages of this power vector representation of a sphero-cylinder lens for numerical and graphical analysis of optometric data are described for problems involving lens combinations, comparison of different lenses, and the statistical distribution of refractive errors.
Longitudinal change of refractive error in infants during the first year of life.
Using cycloplegia, the change in ametropia of 113 infants was followed at 3 month intervals over the first year of life. Scatterplots of the spherical equivalent power show that the dioptric differences exhibit a significant myopic shift of -0.38 ds between 26 and 36 weeks and -0.38 ds between 36 and 52 weeks. The spread of the dioptric differences (95% CI) does not appear to be related to the magnitude of the ametropia present and decreases with time. By 12 months of age the frequency distribution of the spherical equivalent appears to become leptokurtic as it is in the adult. On average the astigmatism was of low degree (less than 1 dioptre cylinder) and with the rule. Anisometropia was rarely seen. The results of this longitudinal study point to an optimal time for screening and perhaps prescribing for 'abnormal' refractive error between 9 and 12 months of age.
The association of strabismus, amblyopia, and refractive errors in spasmus nutans.
PURPOSE: Spasmus nutans is a condition that includes asymmetric nystagmus and occurs during the amblyogenic period. Because specific alterations in early visual experience are known to be associated with changes in visual development, relations between spasmus nutans and abnormal visual sequelae were examined. METHODS: The records of 18 patients with spasmus nutans were reviewed retrospectively. The incidence of strabismus, amblyopia, anisometropia, and astigmatism was compared with published age-matched control subjects. RESULTS: There was a significantly higher incidence of strabismus (10 of 18) and amblyopia (8 of 18) of the eye with the greater amplitude of nystagmus. No correlation of refractive error with lateralization of nystagmus could be established. Twelve of 18 patients required spectacles for improvement in visual acuity and for treatment of amblyopia. Best-corrected visual acuity averaged 1.20 Snellen lines poorer than age-adjusted normative values; however, loss of visual acuity was, in most cases, symmetric and not related to lateralization of nystagmus. CONCLUSION: Early detection and treatment of anticipated abnormal visual issues in patients with spasmus nutans will optimize visual outcomes.
Vision-specific quality of life and modes of refractive error correction.
PURPOSE: Many studies currently use surveys to assess patients' reports of vision-specific quality of life to determine the impact of the disease or the most appropriate mode of treatment. One such instrument, the National Eye Institute Visual Function Questionnaire (NEI-VFQ), was developed to assess vision-related quality of life with respect to emotional well-being and social function as well as difficulty with tasks and symptoms. We administered the NEI-VFQ to 218 subjects free of eye disease to see if the survey was sensitive enough to detect differences in three modes of refractive error correction: spectacles, soft contact lenses, and rigid contact lenses. METHODS: Surveys were administered to 117 rigid contact lens wearers, 51 spectacle wearers, and 50 soft contact lens wearers. Kruskal-Wallis one-way analysis of variance was conducted to determine significant differences in each of the subscales. RESULTS: The Peripheral Vision subscale score (mean +/- SD) was 92.6 +/- 15.2 for the spectacle wearers, 100.0 +/- 0.0 for the soft contact lens wearers, and 98.3 +/- 7.1 for the rigid gas-permeable contact lens wearers; the spectacle wearers' Peripheral Vision score was significantly lower than the other two groups (Wilcoxon rank sum, p < 0.003 for both). The spectacle wearers (96.6 +/- 9.2) also had a significantly lower Dependency subscale score than the rigid contact lens group (99.7 +/- 1.5) (Wilcoxon rank sum, p = 0.001). There were no significant differences between the three groups detected in the mean of any of the other subscale scores. At least 50% of the subjects reported the maximum score for 6 of the 11 subscales. Given our sample size, we have 100% power to detect a difference of 10 points with a SD of 10 at the alpha = 0.05 level. CONCLUSION: The NEI-VFQ is not appropriate for detecting significant differences in vision-related quality of life among spectacle, soft contact lens, and rigid gas-permeable contact lens wearers, primarily due to maximum ratings by many of the subjects.
Minus-power intraocular lenses to correct refractive errors in myopic pseudophakia.
PURPOSE: To evaluate the effectiveness of a secondary, piggyback, minus-power intraocular lens (IOL) to correct the refractive error in patients with myopic pseudophakia. METHODS: In this prospective noncomparative cohort study, 51 myopic pseudophakic patients received implantation of a minus-power IOL as a secondary procedure to correct residual pseudophakic myopia. RESULTS: The mean residual myopia of -3.05 diopters (D) was reduced to -0.38 D. All eyes were within +/- 1.00 D of the desired refraction. Uncorrected visual acuity was 20/40 or better in 72% of eyes, and best corrected visual acuity was 20/40 or better in 96%. Uncorrected visual acuity improved by 2 or more lines in 85% of eyes and by 5 or more lines in 65%. CONCLUSION: Clinical outcomes can now be improved in patients with myopic pseudophakia whose previous options (i.e., lens exchange or refractive surgery) were more traumatic or less predictable.
Differential effects of various causes of deafness on the eyes, refractive errors, and vision of children.
A retrospective study of oculovisual assessment records of the population of three Ontario schools for deaf children assessed the differential effects of various causes of deafness on the prevalence of vision anomalies. Inherited deafness (ID) appears to be associated with the fewest visual anomalies. Congenital rubella (CR) had the greatest prevalence and was associated with the broadest spectrum of ocular and visual problems. It appears to have a significant effect on corneal curvature as well as being associated with anomalies of other organ systems. Children who had had CR, neonatal sepsis (NS), and Rh incompatibility (Rh) all showed higher rates of strabismus and amblyopia. Those who were deaf from meningitis (MEN) or NS showed a tendency to be more hyperopic, whereas the sample with Rh showed a trend toward myopia. The CR children had the broadest range of spherical refractive errors of all the causes of deafness. Children in schools for the deaf are generally those with substantial or profound hearing loss and thus are more likely to have an accompanying vision impairment. Knowledge of the effect on vision of the causes of deafness should aid practitioners in identifying and detecting similar effects on vision when mild or moderate deafness does not require a child's attendance at schools for the deaf.
Refractive error and ocular motility in plagiocephaly.
Plagiocephaly, which is caused by premature closure of one of the coronal sutures, leads to fronto-orbital asymmetry. The aim of this work was to study the repercussions of orbital deformation on the visual system. Twenty-one patients presenting with plagiocephaly at birth and operated on by the same craniofacial technique (bilateral approach with translation and advancement of the entire involved orbits) were included in the study. All of the patients were examined by clinical anthropometry with three-dimensional reconstruction and underwent complete eye examination by the same observer. Follow-up after craniofacial surgery ranged from 15 months to 4 years. In the last few years, three-dimensional reconstruction has shown that the anatomic region affected by the deformation is the frontozygomatic region and has thus made it possible to advance to another theory on the origins of ocular problems. The severe effect of orbital anomalies on the development of the visual system (binocular vision, strabismus with amblyopia, refractive errors) has been emphasized in the literature. The present study shows that the scheduling of reconstructive surgery is fundamental and must not exceed 6 months, given the immaturity of the visual system up until this time. This means that the ophthalmologist must be able to recognize the various craniostenoses in order to schedule reconstructive surgery as soon as possible. Cooperation between the neurosurgeon and the ophthalmologist is of paramount importance if the pathogenic effects of this bone deformation are to be stopped and proper visual development preserved.
Refractive errors and cataract as causes of visual impairment in Brazil.
PURPOSE: To identify the main causes of visual impairment (VA <or= 0.2) within the population over 50 years of age examined in "Cataract Free Zone" projects sponsored by the University of Campinas from 1986 to 1995. METHODS: A retrospective review of the ophthalmic forms used for 60,404 patients examined in 74 Cataract Projects was performed. Through mass media information, adults of the target region or city were asked to self-test their vision. Patients with VA <or= 0.2 in the better eye were to come to a visual acuity test. Using Snellen charts, visual acuity testing was done by trained auxiliaries and medical students. The positive cases were then examined by ophthalmologists Criteria were established for the classification of the diagnoses and statistical analysis was performed. RESULTS: After the self-test of visual acuity, 60,404 patients came to have their visual acuity tested; 11,462 (18.97%) cases were considered positive and were submitted to complete eye examination; 5447 (42.7%) received spectacles for vision improvement, and 2704 (23.59%) had cataract surgery done. Other important causes of visual impairment were senile macular degeneration (5.4%) and glaucoma (4.02%). CONCLUSION: The main causes of visual impairment were non-corrected refractive errors and senile cataract. Ophthalmic community-based campaigns to serve the older population are recommended in order to detect and treat the identified cases and to indicate possible changes in the health care system.
Changes in retinal and choroidal gene expression during development of refractive errors in chicks.
PURPOSE: During growth, the retina analyzes the projected image to achieve a close match between eye length and focal length. Because the messengers released by retina and choroid are largely unknown, genes that are differently expressed in response to changes in the retinal image were identified. In addition, because glucagon may be important in the visual control of eye growth, the transcript levels of proglucagon were studied. METHODS: Reverse transcription-polymerase chain reaction differential display was used to identify genes that were differentially expressed in chick eyes that were deprived of sharp vision or treated with positive or negative lenses. Differences were analyzed through sequencing and database searches and confirmed by Northern blot analyses. RESULTS: Combining 40 and 33 arbitrary primers with 3 oligo-dT-primers, approximately 48% and 40% of the retinal and choroidal mRNAs were screened, respectively. Twelve differences were detected in retinal tissue and five in choroidal tissue after 6 to 24 hours of exposure to defocus. Only one of 10 sequenced products could be identified as cytochrome-c oxidase, subunit I. Northern blot analysis confirmed its twofold upregulation after positive lens wear and also changes in four other unknown genes. Finally, it was shown that retinal glucagon mRNA content increased after treatment with positive lenses. CONCLUSIONS: Visual conditions that induce refractive errors produce changes in gene expression in retina and choroid within 1 day. In line with previous immunohistochemical data, it was found that the amount of glucagon mRNA was upregulated during wearing of positive lenses.
Early changes in refractive error following radial keratotomy.
One hundred twenty-six eyes that had undergone radial keratotomy were analyzed to assess the early changes in refractive error after surgery. Between two weeks and three months, 38% of eyes became more myopic by less than 1 diopter (D), 34% by 1.00 to 1.87 D, and 25% by 2.00 to 3.50 D. Four eyes (3%) had a decrease of 0.25 to 1.25 D. The average increase between two weeks and three months was 1.31 D (SD, 0.9 D). To decrease this change, 15 eyes were semi-pressure patched at night and treated with topical steroids for four weeks following surgery. The average change between two weeks and three months in these eyes was 0.3 D (SD, 1.0 D). This retrospective study suggests that semi-pressure patching after surgery may be useful for eyes that are undercorrected or overcorrected by less than 1 D.
The effect of the correction of refractive errors on nonparalytic esotropia.
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[Unusual congenital refractive error with compensatory mono-ocular motility].
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