Image quality in polypseudophakia for extremely short eyes.
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AIM: To evaluate the image quality produced by polypseudophakia used for strongly hypermetropic and nanophthalmic eyes. METHODS: Primary aberration theory and ray tracing analysis were used to calculate the optimum lens shapes and power distribution between the two intraocular lenses for two example eyes: one a strongly hypermetropic eye, the other a nanophthalmic eye. Spherical aberration and oblique astigmatism were considered. Modulation transfer function (MTF) curves were computed using commercial optical design software (Sigma 2100, Kidger Optics Ltd) to assess axial image quality, and the sagittal and tangential image surfaces were computed to study image quality across the field. RESULTS: A significant improvement in the axial MTF was found for the eyes with double implants. However, results indicate that this may be realised as a better contrast sensitivity in the low to mid spatial frequency range rather than as a better Snellen acuity. The optimum lens shapes for minimum spherical aberration (best axial image quality) were approximately convex-plano for both lenses with the convex surface facing the cornea. Conversely, the optimum lens shapes for zero oblique astigmatism were strongly meniscus with the anterior surface concave. Correction of oblique astigmatism was only achieved with a loss in axial performance. CONCLUSIONS: Optimum estimated visual acuity exceeds 6/5 in both the hypermetropic and the nanophthalmic eyes studied (pupil size of 4 mm) with polypseudophakic correction. These results can be attained using convex-plano or biconvex lenses with the most convex surface facing the cornea. If the posterior surface of the posterior intraocular lens is convex, as is commonly used to help prevent migration of lens epithelial cells causing posterior capsular opacification (PCO), then it is still possible to achieve 6/4.5 in the hypermetropic eye and 6/5.3 in the nanophthalmic eye provided the anterior intraocular lens has an approximately convex-plano shape with the convex surface anterior. It was therefore concluded that consideration of optical image quality does not demand that additional intraocular lens shapes need to be manufactured for polypseudophakic correction of extremely short eyes and that implanting the posterior intraocular lens in the conventional orientation to help prevent PCO does not necessarily limit estimated visual acuity. (+info)
Refractive errors in a black adult population: the Barbados Eye Study.
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PURPOSE: To describe the prevalence of refractive errors in a black adult population. METHODS: The Barbados Eye Study, a population-based study, included 4709 Barbados-born citizens, or 84% of a random sample, 40 to 84 years of age. Myopia and hyperopia were defined as a spherical equivalent <-0.5 diopters and >+0.5 diopters, respectively, based on automated refraction. Analyses included 4036 black participants without history of cataract surgery. Associations with myopia and hyperopia were evaluated in logistic regression analyses. RESULTS: The prevalence of myopia was 21.9% and was higher in men (25.0%) than in women (19.5%). The prevalence of hyperopia was 46.9% and was higher in women (51.8%) than in men (40.5%). The prevalence of myopia decreased from 17% in persons 40 to 49 years of age to 11% in those 50 to 59 years of age, but increased after 60 years of age. The prevalence of hyperopia increased from 29% at 40 to 49 years of age to 65% at 50 to 59 years of age, and tended to decline thereafter. A higher prevalence of myopia was positively associated (P < 0.05) with lifetime occupations requiring nearwork, nuclear opacities, posterior subcapsular opacities, glaucoma, and ocular hypertension. Factors associated with hyperopia were the same as for myopia, except for occupation, and in the opposite direction. CONCLUSIONS: High prevalences of myopia and hyperopia were found in this large black adult population. The prevalence of myopia (hyperopia) increased (decreased) after 60 years of age, which is inconsistent with data from other studies. The high prevalence of age-related cataract, glaucoma, and other eye conditions in the Barbados Eye Study population may contribute to the findings. (+info)
Effect of spectacles on changes of spherical hypermetropia in infants who did, and did not, have strabismus.
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AIM: To explore why emmetropisation fails in children who have strabismus. METHODS: 289 hypermetropic infants were randomly allocated spectacles and followed. Changes in spherical hypermetropia were compared in those who had strabismus and those who did not. The effect of wearing glasses on these changes was assessed using t tests and regression analysis. RESULTS: Mean spherical hypermetropia decreased in both eyes of "normal" children (p<0.001). The consistent wearing of glasses impeded this process in both eyes (p<0.007). In the children with strabismus, there were no significant changes in either eye, irrespective of treatment (p>0. 05). CONCLUSIONS: In contrast with normal infants, neither eye of those who had strabismus emmetropised, irrespective of whether the incoming vision was clear or blurred. It is suggested that these eyes did not "recognise" the signal of blurred vision, and that they remained long sighted because they were destined to squint. Hence, the children did not squint because they were long sighted, and glasses did not prevent them squinting. (+info)
Six-month results of hyperopic and astigmatic LASIK in eyes with primary and secondary hyperopia.
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PURPOSE: To assess the safety and efficacy of laser in situ keratomileusis (LASIK) for hyperopia and hyperopic astigmatism and develop a LASIK nomogram for primary hyperopia or hyperopia secondary to myopic refractive surgery using the VISX STAR S2. METHODS: Prospective evaluation of LASIK in 46 primary eyes and 29 secondary eyes with fogged manifest sphere from +0.5 diopters (D) to +6.0 D and cylinder from 0 to +5.0 D. RESULTS: Mean manifest spherical equivalent (SE) in patients with primary hyperopia was +2.50 D +/- 0.93 preoperatively and +0.70 D +/- 1.19 at 6 months. At 6 months, 79% of primary hyperopes had uncorrected visual acuity (UCVA) of 20/40 or better; 63% were within +/- 1 D of emmetropia. One primary hyperope lost 2 lines of best spectacle-corrected vision (BCVA) at 1 month. Complications included transient epithelial defect (6.5%), epithelial cells in the interface (4.3%), diffuse lamellar keratitis (4.3%), haze (2.2%), and mild irregular astigmatism (2.2%). In those with secondary hyperopia, mean manifest SE was +1.70 D +/- 0.82 preoperatively and -0.27 D +/- 0.95 at 6 months. At 6 months, 83% of secondary hyperopes had UCVA of 20/40 or better; 74% were within +/- 1 D of emmetropia. No secondary hyperope lost > or = 2 lines of BCVA. Complications included intraoperative bleeding (3.4%), intraoperative epithelial defect (3.4%), transient interface debris (3.4%), significant dry eye (3.4%), blood in interface (3.4%), irregular astigmatism (6.9%), slight decentration (6.9%), trace haze (6.9%), mild epithelial ingrowth not requiring removal (3.4%), or corneal irregularity (3.4%). CONCLUSION: These early data suggest that LASIK for hyperopia from +0.5 to +6 D and astigmatism from 0 to +5 D using the VISX STAR S2 benefits from a nomogram adjusted for preoperative refraction, age, and prior refractive surgery and is safe and effective. Patients with secondary hyperopia achieved more correction than those with primary hyperopia, although the accuracy and predictability of LASIK in both groups has improved with the nomogram adjustments. (+info)
Peripheral refraction and ocular shape in children.
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PURPOSE: To evaluate the relation between ocular shape and refractive error in children. METHODS: Ocular shape was assessed by measuring relative peripheral refractive error (the difference between the spherical equivalent cycloplegic autorefraction 30 degrees in the nasal visual field and in primary gaze) for the right eye of 822 children aged 5 to 14 years participating in the Orinda Longitudinal Study of Myopia in 1995. Axial ocular dimensions were measured by A-scan ultrasonography, crystalline lens radii of curvature by videophakometry, and corneal power by videokeratography. RESULTS: Myopic children had greater relative hyperopia in the periphery (+0.80 +/- 1.29 D), indicating a prolate ocular shape (longer axial length than equatorial diameter), compared with relative peripheral myopia and an oblate shape (broader equatorial diameter than axial length) for emmetropes (-0.41 +/- 0.75 D) and hyperopes (-1.09 +/- 1.02 D). Relative peripheral hyperopia was associated with myopic ocular component characteristics: deeper anterior and vitreous chambers, flatter crystalline lenses that were smaller in volume, and steeper corneas. Lens thickness had a more complex association. Relative peripheral hyperopia was associated with thinner lenses between refractive error groups but changed in sign to become associated with thicker lenses when analyzed within each refractive error group. Receiver operator characteristics analysis of the ocular components indicated that vitreous chamber depth was the most important ocular component for characterizing the myopic eye, but that peripheral refraction made a significant independent contribution. CONCLUSIONS: The eyes of myopic children were both elongated and distorted into a prolate shape. Thinner crystalline lenses were associated with more hyperopic relative peripheral refractions across refractive error groups, but failure of the lens to thin may account for the association between thicker lenses and more hyperopic relative peripheral refractions within a given refractive group. Increased ciliary-choroidal tension is proposed as a potential cause of ocular distortion in myopic eyes. (+info)
Choroidal thickness changes during altered eye growth and refractive state in a primate.
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PURPOSE: In the chick, compensation for experimentally induced defocus involves changes in the thickness of the choroid. The choroid thickens in response to imposed myopic defocus and thins in response to imposed hyperopic defocus. This study was undertaken to determine whether similar choroidal changes occur in the primate eye with induced refractive errors. METHODS: Thirty-three common marmosets were used. Eyes in 26 monkeys served as untreated control eyes, and eyes in 7 received 3 weeks of monocular lid suture to induce changes in eye growth and refractive state. Refractive errors were measured using refractometry and retinoscopy, and axial ocular dimensions, including choroidal thickness, were measured using high-frequency A-scan ultrasonography. Eyes were measured before the lids were sutured and at frequent intervals after lid opening. RESULTS: In the marmoset, choroidal thickness ranges from 88 to 150 microm and increases significantly during the first year of life. Monocular lid suture initially results in short, hyperopic eyes that then become elongated and myopic. In these animals the choroids of both the experimental and the fellow control eyes also increase in thickness with age but additionally show interocular differences that vary significantly with the relative changes in vitreous chamber depth and refraction. In eyes that are shorter and more hyperopic than control eyes the choroids are thicker, and in eyes that are longer and more myopic than control eyes the choroids are thinner. CONCLUSIONS: In marmosets, the thickness of the choroid increases during postnatal eye growth. Superimposed on this developmental increase in choroidal thickness there are changes in thickness that are correlated with the induced changes in eye size. These changes are small (<50 microm) in comparison with those observed in the chick, contributing to less than a diopter change in refractive error. (+info)
Vision-dependent changes in the choroidal thickness of macaque monkeys.
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PURPOSE: To determine whether changes in the eye's effective refractive state produce changes in the thickness of the choroid in infant monkeys. METHODS: Normal developmental changes in choroidal thickness were studied in 10 normal rhesus monkeys. Hyperopia or myopia was induced by rearing 26 infant monkeys with either spectacle or diffuser lenses secured in front of one or both eyes. The treatment lenses were worn continuously beginning at approximately 3 weeks of age for an average of 120 days. Refractive status and ocular axial dimensions, including choroidal thickness, were measured by retinoscopy and high-frequency A-scan ultrasonography, respectively. RESULTS: Three lines of evidence indicate that the normal increase in choroidal thickness that occurs during early maturation can be altered by the eye's refractive state. First, in monkeys experiencing form deprivation or those in the process of compensating for imposed optical errors, choroidal thickness and refractive error were significantly correlated with eyes developing myopia having thinner choroids than those developing hyperopia. Second, the choroids in eyes recovering from binocularly induced myopia increased in thickness at a faster rate than the choroids in recovering hyperopic eyes. Third, monkeys recovering from induced anisometropias showed interocular alterations in choroidal thickness that were always in the appropriate direction to compensate for the anisometropia. These changes in choroidal thickness, which were on the order of 50 microm, occurred quickly and preceded significant changes in overall eye size. CONCLUSIONS: Changes in the eye's effective refractive state produce rapid compensating changes in choroidal thickness. Although these choroidal changes are small relative to the eye's refractive error, they may play an important role in the visual regulation of axial growth associated with emmetropization. (+info)
Outcome in refractive accommodative esotropia.
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AIM: To examine outcome among children with refractive accommodative esotropia. METHODS: Children with accommodative esotropia associated with hyperopia were included in the study. The features studied were ocular alignment, amblyopia, and the response to treatment, binocular single vision, requirement for surgery, and the change in refraction with age. RESULTS: 103 children with refractive accommodative esotropia were identified. Mean follow up was 4.5 years (range 2-9.5 years). 41 children (39.8%) were fully accommodative (no manifest deviation with full hyperopic correction). The remaining 62 children (60.2%) were partially accommodative. At presentation 61.2% of children were amblyopic in one eye decreasing to 15.5% at the most recent examination. Stereopsis was demonstrated in 89.3% of children at the most recent examination. Mean cycloplegic refraction (dioptres, spherical equivalent) remained stable throughout the follow up period. The mean change in refraction per year was 0.005 dioptres (D) in right eyes (95% CL -0. 0098 to 0.02) and 0.001 D in left eyes (95% CL -0.018 to 0.021). No patients were able to discard their glasses and maintain alignment. CONCLUSIONS: Most children with refractive accommodative esotropia have an excellent outcome in terms of visual acuity and binocular single vision. Current management strategies for this condition result in a marked reduction in the prevalence of amblyopia compared with the prevalence at presentation. The degree of hyperopia, however, remains unchanged with poor prospects for discontinuing glasses wear. The possibility that long term full time glasses wear impedes emmetropisation must be considered. It is also conceivable, however, that these children may behave differently with normal and be predestined to remain hyperopic. (+info)