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Motion thresholds were determined for the fovea and peripheral retina with and without correction for peripheral refractive error. With correction, motion thresholds decreased and inidividual differences disappeared. These results imply that under normal observation conditions, peripheral sensitivity is limited mainly by dioptric rather than retinal variables.
BACKGROUND: A small but significant increase in myopia after extended wear of low oxygen permeability (Dk) hydrogel lenses has been previously reported; however, the specific impact of hypoxia on refractive status and corneal curvature with extended wear are not well documented. THE PURPOSE of this study was to compare the refractive changes induced over a period of 9 months' extended wear with high-Dk fluorosiloxane hydrogel lenses and low-Dk hydrogel lenses. METHODS: Adapted daily wear contact lens wearers were randomly assigned to one of two groups. The low-Dk group wore etafilcon A (Dk = 28) for up to 7 days and 6 nights and the high-Dk group wore lotrafilcon A (Dk = 140) for up to 30 days and nights. Refractive error and corneal curvature were measured at 3-month intervals over 9 month of extended wear. RESULTS: The etafilcon A group demonstrated an average increase in myopia of 0.30 D over the 9 months period; however, no change in spherical myopic correction was measured in the lotrafilcon A group. The cylindrical component did not change in either group. A stratified analysis revealed a greater increase in myopia for low myopes than moderate myopes in the etafilcon A group but no difference in the lotrafilcon A group. Keratometric analysis revealed no change in the etafilcon A group and a small degree of central corneal flattering in both major meridians of 0.35 D in the lotrafilcon A group. CONCLUSIONS: Nine months of extended wear of low-Dk lenses is associated with a small degree of myopic progression in adult myopes that appears to be reversible. Wearing fluorosiloxane-hydrogel lenses of high-Dk had no impact on refractive error and may be associated with a small degree of central corneal flattering.
The refractive error of 186 eyes with choroidal neovascularization (CNV) secondary to age-related macular degeneration (ARMD) was determined. It was found that the risk for the development of this form of ARMD increased with increasing degrees of hyperopia. The 96 patients afflicted with bilateral CNV were significantly older than the unilaterally affected patients (P = 0.027). Abnormal choroidal perfusion was identified in 66.4% of the fluorescein angiograms. These findings support the concept that hyperopic shortening in eyes afflicted with ARMD might cause secondary changes in the choroidal vasculature, predisposing them to choroidal neovascularization.
PURPOSE: There is evidence that the inner retina is involved in eye growth control processes and the development of myopia. We sought to investigate the response dynamics of the inner retina of adult emmetropes and myopes using the global flash multifocal electroretinogram (mfERG) paradigm. METHODS: Fourteen myopes and 10 emmetropic subjects (mean age: 21.0+/-2.8 years) underwent mfERG testing using VERIS 5.1.5X. The global flash stimulus array consisted of 103-scaled hexagons which flickered according to a pseudorandom binary m-sequence (2(13)-1). The stimulation sequence was modified by inserting three frames, a dark frame, a global (full screen) flash, and another dark frame. The amplitude and implicit time of the two distinct waveform features, an early direct component (DC) and a later induced component (IC) of the first-order kernel were analyzed. Retinal responses were averaged over rings of increasing eccentricity, or into nasal and temporal hemifields. RESULTS: There was a significant correlation between the DC and IC response amplitude and myopic refractive error, i.e., the greater the myopic error, the greater the response amplitude. However, when comparing between the two refractive error groups, DC and IC response amplitudes of emmetropes and myopes were similar, even after compensating for the effect of axial length. There were no significant differences in implicit times of the DC and IC in emmetropes and myopes. CONCLUSIONS: Global flash mfERG responses of emmetropes and myopes were not found to be significantly different. The measured retinal adaptation response however varied according to the degree of myopia. We hypothesize that dopamine, a neurotransmitter that plays a key role in retinal adaptation and is known to be reduced in myopic eyes, may be involved in the retinal adaptation effect observed.
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PURPOSE: To examine (1) reproducibility of cycloplegic retinoscopy (C-RNS), cycloplegic autorefraction (C-Autoref), and noncycloplegic autorefraction (NC-Autoref), and (2) validity of C-Autoref and NC-Autoref compared with C-RNS in preschoolers with astigmatism. METHODS: Subjects were 36 Native American preschoolers. Three measurements of right eye refractive error were obtained with each of three methods: C-RNS (by three different retinoscopists), C-Autoref, and NC-Autoref (Nikon Retinomax K+). Vector methods (vector dioptric distance, VDD) were used in the analyses. RESULTS: Mean reproducibility was 0.41 D (SD = 0.18) for C-RNS, 0.25 D (SD = 0.17) for C-Autoref, and 0.37 D (SD = 0.21) for NC-Autoref. Mean agreement between C-Autoref and C-RNS ranged from 0.51 to 0.61 VDD (SD = 0.24 to 0.35), and ranged from 1.66 to 1.74 VDD (SD = 1.11 to 1.25) for agreement between NC-Autoref and C-RNS. Mean bias was -0.07 +0.21 x 149 and -1.33 +0.34 x 178 for C-Autoref and NC-Autoref, respectively. CONCLUSIONS: C-Autoref provided reliable and valid measurements of refractive error in young children. NC-Autoref measurements were reliable within subjects, but there was large variability in validity among subjects.
PURPOSE: To describe the relationship of refractive errors and axial ocular dimensions and age-related cataract. METHODS: Population-based, cross-sectional survey of ocular diseases among Chinese men and women aged 40 to 81 years (n = 1232) living in the Tanjong Pagar district in Singapore. As part of the examination, refraction and corneal curvature were determined with an autorefractor, with refraction further refined subjectively. Ocular dimensions, including axial length, anterior chamber depth, lens thickness, and vitreous chamber depth, were measured with an A-mode ultrasound device. Lens opacity was graded clinically according to the Lens Opacity Classification System (LOCS) III system. Refraction, biometry, and cataract data on right (n = 989) and left (n = 995) eyes were analyzed separately. RESULTS: In analyses controlling for age, gender, education, diabetes, and cigarette smoking, nuclear cataract was associated with myopia (-1.35 D vs. -0.11 D, P < 0.001, comparing right eyes with and without nuclear cataract), but not with any specific biometric component. Cortical cataract was associated with thinner lenses (4.67 mm vs. 4.79 mm, P = 0.001, comparing right eyes with and without cortical cataract), but not with refraction and other biometric components. Posterior subcapsular cataract was associated with myopia (-1.80 D vs. -0.39 D, P < 0.001, comparing right eyes with and without posterior subcapsular cataract), deeper anterior chamber (3.00 mm vs. 2.89 mm, P = 0.02), thinner lens (4.62 mm vs. 4.77 mm, P = 0.001), and longer vitreous chamber (15.78 mm vs. 15.57 mm, P = 0.09), but not with overall axial length and corneal curvature. Adjustment for vitreous chamber depth attenuated the association between posterior subcapsular cataract and myopia by 65.5%, but did not substantially change the association between nuclear cataract and myopia. CONCLUSIONS: These population-based data support the associations between nuclear and posterior subcapsular cataracts and myopia reported in previous studies. Posterior subcapsular cataract is also associated with deeper anterior chamber, thinner lens, and longer vitreous chamber, with vitreous chamber depth explaining most of the association between posterior subcapsular cataract and myopia.
PURPOSE: To evaluate the development of refractive error and axial length in a primate model of sensory strabismus and nystagmus. METHODS: Four macaque monkeys had alternating tarsorraphy beginning within 24 hours of birth. One eye was closed for 25 days, and when it opened, the second eye immediately was closed for the next 25 days. Cycloplegic refractions and axial lengths were determined prospectively for three animals for 1 year or more. These data were compared to those of three unsutured control macaques raised under otherwise similar conditions. RESULTS: Each experimental animal developed exotropia and nystagmus. The first occluded eyes were significantly more hypermetropic than the control eyes at 1 month of age (+7.25 D +/- 1.95 D versus +1.92 D +/- 1.27 D; P < 0.02) and remained significantly more hypermetropic throughout the study. The second occluded eyes were more hypermetropic than the control eyes at 1 month (+2.42 D +/- 2.13 D versus +1.92 D +/- 1.27 D; P = 0.20), but less hypermetropic than the first occluded eyes. The rate of emmetropization was slightly faster for the first occluded eyes than for the control eyes (-0.12 D/month compared to -0.03 D/month). The mean axial length measurements of the experimental and control eyes were the same at 1 month, and their rates of change over time were identical. CONCLUSIONS: Persistent hypermetropia was produced by a brief period of reverse neonatal eyelid closure in a model of congenital-like nystagmus. It is suggested that infantile lid closure, nystagmus, or amblyopia after neonatal visual disruption may be associated with a failure of normal emmetropization.
Studies of the relationship of clinical and laboratory measures of accommodation and convergence function with refractive error are reviewed. There are inconsistencies in results from study to study presumably due, in part, to methodological differences. However, some basic trends can be outlined. In studies in young adults, accommodation in darkness (dark focus), optical reflex accommodation, and proximally induced accommodation are less in myopes than in emmetropes and hyperopes. It also appears that nearpoint esophoria is associated with higher rates of myopia progression in children. Implications for myopia etiology are discussed.
Recently, alterations in contrast (modulation) sensitivity functions of patients with high refractive errors have been noted. For example, this seems to be a common finding in aphakia. In some measure the observed alterations are due to the effect of the corrective lens and the optics of the eyes. These optical effects (in addition to blur) must be factored out in order to determine whether residual effects on the visual system remain. The argument is applicable to photographs of sine wave fringes as well as devices designed to produce interference patterns directly on the retina. A simple means for largely correcting these lens effects is discussed.
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PURPOSE: This investigation studied the factors involved in the development of refractive error (RE) in premature infants unaffected by retinopathy of prematurity (ROP). METHODS: Premature infants enrolled in the national ROP screening program were recruited and examined at 32, 36, 40, 44, and 52 weeks' postmenstrual age. At each examination, axial length (AXL), anterior chamber depth (ACD), and lens thickness (LT) were measured on the A-scan biometer. Corneal curvature (CC) was recorded with a video-ophthalmophakometer, and refractive state was determined with routine cycloplegic refraction. Multilevel modeling techniques were used to determine the relationships between all the variables throughout the study period, as well as individual growth rates. RESULTS: Sixty-eight premature infants were included. AXL and ACD showed linear patterns of growth, whereas LT changed little over the study period. CC showed a quadratic growth pattern, and unlike the previous variables, correlated well with refractive state. Premature infants were myopes at the start of the study, with refraction becoming emmetropic as they neared full term and then hypermetropic toward the end of the study. CONCLUSIONS: Most of the components of refractive status showed linear patterns of growth during this early phase of ocular development. CC displayed a more complex pattern of growth, which correlated well with refractive state. Compared with full-term infants examined around term, this group has shorter AXLs, shallower anterior chambers, and more highly curved corneas. In addition, less of the expected hypermetropia developed in the premature group, which seems mainly due to the differences in ACD and corneal curvature.
AIMS: To evaluate the relationship between amplitude of accommodation and refractive errors in the peri-presbyopic age group. MATERIALS AND METHODS: Three hundred and sixteen right eyes of 316 consecutive patients in the age group 35-50 years who attended our outpatient clinic were studied. Emmetropes, hypermetropes and myopes with best-corrected visual acuity of 6/6 J1 in both eyes were included. The amplitude of accommodation (AA) was calculated by measuring the near point of accommodation (NPA). In patients with more than +/- 2 diopter sphere correction for distance, the NPA was also measured using appropriate soft contact lenses. RESULTS: There was a statistically significant difference in AA between myopes and hypermetropes (P < 0.005) and between myopes and emmetropes (P < 0.005) in the 35-39 year age group. In the 40-44 year age group, there was a significant difference in AA between emmetropes and hypermetropes (P < 0.0001), emmetropes and myopes (P < 0.01) and hypermetropes and myopes (P < 0.0001). In patients above 45 years of age there was no significant difference (P > 0.5). CONCLUSION: Our study showed higher amplitude of accommodation among myopes between 35 and 44 years compared to emmetropes and hypermetropes.
The association of a large axial length with a small refractive error and a normal corneal diameter should alert the lens implant surgeon to the possibility that goniomegaly is present. We report a patient whose intraoperative anterior chamber diameter was measured as 15 mm. It was necessary to insert a modified posterior chamber intraocular lens instead of an anterior chamber lens.
PURPOSE: To determine if refractive errors influence the association of blood pressure and retinal vessel diameters. DESIGN: Population-based, cross-sectional study. METHODS: Retinal photographs from the right eyes of participants (n = 3,654, aged 49+ years) in the Blue Mountains Eye Study taken during baseline examinations (1992 to 1994) were digitized. The diameter of all retinal vessels located half to one disk diameter from the disk margin was measured using a computer-assisted imaging program. These measurements were combined to provide the average diameters of retinal arterioles and venules of that eye, and the ratio of their diameters, the arteriole-to-venule ratio (AVR). The association of blood pressure and retinal vessel diameters was analyzed before and after correction for refraction using the Bengtsson formula. RESULTS: Before correction, each 10-mm Hg increase in mean arterial blood pressure was associated with a 3.7-microm (95% confidence interval [CI], 3.2-4.3) decrease in arteriolar diameter and a 0.9-microm (95% CI, 0.3-0.9) decrease in venular diameter. After correction for refraction, each 1-mm Hg increase in mean arterial blood pressure was associated with a 3.7-microm (95% CI, 3.2-4.2) decrease in arteriolar diameter and a 0.8-microm (95% CI, 0.3-0.9) decrease in venular diameter. Refraction was not associated with the AVR and had no effect on the association of blood pressure and AVR. CONCLUSION: Refraction had no appreciable effect on the association of blood pressure and retinal vessel diameters or on the AVR. Correction for refraction is important for quantifying absolute retinal vessel caliber, but may not be particularly important in epidemiologic studies investigating the association of generalized retinal arteriolar narrowing and hypertension.
OBJECTIVE: This study aimed to evaluate the effect of intraoperative corneal cauterization on the postkeratoplasty refraction of patients with keratoconus. DESIGN: A randomized clinical trial. PARTICIPANTS: Thirty eyes of 29 patients with keratoconus undergoing standard penetrating keratoplasty by the same surgeon were evaluated (MB). INTERVENTION: Standard penetrating keratoplasty included the use of an 8.0-mm donor button sutured into a 7.5-mm recipient bed by means of two running 10-0 nylon sutures with 16 bites each. Before trephination of the recipient bed, superficial cauterization causing tissue shrinkage was applied to a 6-mm central area of the cornea of only 15 eyes (group A). The remaining 15 eyes (group B) did not undergo intraoperative cauterization. Before surgery, 6 months, and 13 months after surgery, a complete ophthalmologic examination was performed on each patient, including uncorrected and best-corrected visual acuity, refraction, keratometry, computerized corneal topography, as well as A-scan contact ultrasonography. MAIN OUTCOME MEASURES: Postkeratoplasty refractive error was measured. RESULTS: Both 6 months (sutures still in place) and 13 months (suture removal performed in all patients) after surgery, the average spherical equivalent was significantly less myopic in the patients undergoing cauterization. At 6 months, it was +1.72 diopters (D) +/- 1.13 D in group A and -3.16 D +/- 2.84 D in group B; at 13 months, it was +0.09 D 1.52 D in group A and -3.89 D +/- 3.01 D in group B. The average keratometric astigmatism also was significantly lower in group A than in group B both at 6 (2.5 D +/- 1.6 D vs. 4.1 D +/- 2.3 D) and 13 months (2.7 D +/- 1.5 D vs. 4.4 D +/- 2.4 D) after surgery. CONCLUSION: Cauterization of the central cornea improves the postkeratoplasty refractive results of patients with keratoconus.
Localization of single stimuli presented individually on the circumference of an imaginary circle was determined with and without three diopters of refractive error introduced by spherical lenses. The presence of blur had no effect on localization accuracy.