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PubMed2002

Use of a portable topography machine for screening donor tissue for prior refractive surgery.

PURPOSE: We investigated whether a portable, hand-held topography unit could be used to measure corneal topography either at the donor site or in the laboratory and whether the technology could be used to screen donor eye tissue for prior refractive surgery. METHODS: The corneal topography of 22 eyes of 12 normal donors was measured with the Keratron Scout portable topography machine before and after whole-eye enucleation. Field and laboratory measurements of central curvature, astigmatism, and the difference between the corneal curvature at the 7-mm and the 3-mm zone were compared. The 7-mm and 3-mm zone curvature differences were also used to screen for eyes that had undergone refractive surgery. RESULTS: The mean central curvature of the normal eyes in the field [43.28 +/- 1.58 diopter (D)] was not significantly different from the mean curvature in the laboratory (43.52 +/- 1.72 D; p= 0.20). Field and laboratory astigmatism was 2.02 +/- 1.13 D and 1.64 +/- 1.38 D, respectively (p = 0.26, not significant). The eyes had a normal prolate shape, with the corneal power less in the periphery than in the center (mean difference between the 7-mm and 3-mm zone of -1.48 +/- 0.83 D in the field and -1.77 +/- 0.73 D in the lab; = 0.069). Field and laboratory measurements of corneal shape correlated well with each other. Eight of eight eyes with refractive surgery for myopia and one of two eyes with hexagonal keratotomy for hyperopia were outside 2 SD of the normal range. CONCLUSION: The Scout can be used to measure corneal topography at the donor site and in the eye bank laboratory with comparable results. Regional power differences between the corneal periphery and center could be used as a method for screening donor eyes for prior refractive surgery.

Aged↗
PubMed2000

LASIK enhancements.

As the field of refractive surgery continues to evolve, an increasing number of surgical options are available for LASIK enhancements. Nonetheless, older methods such as AK continue to play an important role in enhancement procedures. Improvements in instruments and techniques allow for previously made LASIK flaps to be safely lifted for additional myopic or hyperopic ablations. Newer methods such as Intacs placement provide an effective option for patients who are not good candidates for further ablative procedures. These advancements allow refractive surgeons to treat a wider range of myopia, hyperopia, and astigmatism effectively in eyes with a history of LASIK surgery.

Cornea↗
PubMed1979

The effect of cycloplegia on the determination of refractive error by the Ophthalmetron.

The Ophthalmetron was used to measure the refractive error of 10 male optometry students. Although there was a high incidence of invalid readings, more repeatable results were obtained with use of a cycloplegic. Measurements made under cycloplegia revealed 0.41 D more hyperopia but no differences in astigmatism as compared to the noncycloplegic refraction. Instrument myopia was shown not to be a factor.

Accommodation, Ocular↗
PubMed1984

Pseudoretinitis pigmentosa.

A 52-year-old black male with Duane's retraction syndrome and fundus pigmentation was examined. The patient had high hyperopia and reported ocular problems in other family members. A battery of tests indicated that the pigmentary anomalies were not due to retinitis pigmentosa.

Duane Retraction Syndrome↗
PubMed1987

Comparison of visual characteristics in children with and without learning difficulties.

This report compares the refractive status, visual acuity, binocular status, vergence/accommodation facility, perceptual skills, and ocular health of 261 children with learning difficulties (LD) and 496 No-LD children, all between the ages of 6 and 12 years. Data reveal that among conditions diagnosed routinely by optometrists, hyperopia and perceptual skills dysfunction were more prevalent in LD children and myopia in No-LD children. No other significant between-group differences were found.

Astigmatism↗
PubMed1988

Refraction and its components in Melanesian schoolchildren in Vanuatu.

Refraction and its components were measured on 788 Melanesian children and 39 children of other races, aged 6 through 19 years, in the South Pacific island nation of Vanuatu. Of the 788 Melanesian children, 766 (97.2%) were found to have uncorrected visual acuity of 6/6 or better, and 763 (96.8%) were found to have a spherical equivalent refraction between -0.25 and +1.00 D. Only 23 (2.9%) Melanesian children were found to have myopia greater than 0.25 D, only 2 (0.3%) were found to have hyperopia greater than 1.00 D, and only 2 (0.3%) were found to have refractive astigmatism greater than 1.00 D. Mean corneal refracting power was greater for girls than for boys, at all ages, but did not appear to change in any regular manner with age. Mean axial length and mean vitreous length were greater for boys than for girls, at all ages, each increasing approximately 1.0 mm from age 6 and 7 years to age 18 and 19 years. Although the low prevalence of ametropia may be considered to be due mainly to genetic factors, the possibility of environmental factors cannot be excluded.

Adolescent↗
PubMed1990

Screening infant vision with paraxial photorefraction.

Early screening for refractive errors is highly desirable. Techniques for doing this must be usable with noninstructable subjects (infants), noninvasive, and relatively easy to use. Photorefraction has been used to examine infants' refractive status. However, unless cycloplegia is used, the results can be difficult to evaluate, inasmuch as the subject's plane of focus is not known. This paper describes a photorefraction system that is being used for routine screening of young infants, without cycloplegia and without using highly skilled personnel. The major innovation is the systematic presentation of attractive targets at distances that present a range of demands to accommodation. Changes in the fundal reflections, seen in the photographs taken as the infant views the different targets, can be interpreted unequivocally to identify severe myopia and hyperopia, anisometropia, heterotropia, and anisocoria. The results can also be quantified and are compared with retinoscopic refractions.

Clinical Protocols↗
PubMed1990

The Video Display Terminal Eye Clinic: clinical report.

The Video Display Terminal Eye Clinic was designed to relieve the symptoms of video display terminal users by diagnosing and treating visual problems and by analyzing the patients' work station environment through an in-office simulation and making suggestions for improvements. The Clinic was open to the public and patients were therefore self-selected. The symptoms, diagnoses, and treatments were compiled retrospectively and reported for 153 patients. Vision problems were diagnosed in most patients. The most frequent diagnoses included: presbyopia, improper spectacle design for presbyopia, accomodative deficiencies, esophoria, exophoria, and hyperopia. The results suggest that proper visual care and work station arrangement can improve comfort.

Accommodation, Ocular↗
PubMed1990

Survey of spectacle wear and refractive error prevalence in USAF pilots and navigators.

A retrospective survey of 5000 active aircrew records was performed at 12 United States Air Force (USAF) bases to obtain information about the prevalence of spectacle wear and refractive error. The data revealed that 27.4% of pilots and 51.5% of navigators/weapons systems operators (Nav/WSO) required spectacles when flying. Of the spectacle-wearing pilots, 12.4% required bifocals. Myopia was the predominant refractive error and a relatively large percentage of aircrew members had astigmatism of 0.75 D or more, e.g., 33.1% of pilots. At the time of entry into the USAF, refractive error data were clustered around emmetropia with a definite skew toward hyperopia.

Adult↗
PubMed1991

Optometric findings in the fragile X syndrome.

Fragile X syndrome (fra X) is one of the most significant discoveries in the area of mental retardation in the past 2 decades. Although hundreds of articles and two text-books have been written on the subject, only two studies have been published in the ophthalmic literature. This paper provides a brief review of the syndrome and reports on the ocular findings of 30 subjects with this genetic abnormality. We found that 30% of the subjects exhibited strabismus. Of those with strabismus, 70% were esotropes. Fifty-nine percent of the eyes evaluated (N = 58) showed hyperopia of +1.00 D or greater, 17% myopia of -1.00 D or greater, and 22% had at least 1.00 D of astigmatism. Major ocular health abnormalities were not identified in any of our subjects. The optometrist, as the primary eye care provider, should diagnose and treat these oculo-visual dysfunctions.

Adolescent↗
PubMed1995

Evaluation of vision services delivered by a mobile eye clinic in Costa Rica.

A number of private voluntary organizations provide mobile eye services to underserved populations in the developing world. This paper seeks to determine what segment of the population makes use of mobile vision clinics and whether the clinics are identifying significant eye conditions previously undetected by local eye care providers. The population studied were those attending the 1989 vision screening project conducted in rural Costa Rica by members of Volunteer Optometric Services to Humanity (VOSH). Sources of data include patient records of clinic attendees (N = 1530), patient interviews, and Costa Rican census data. Most of the clinic attendees were female (56.9%), over 35 years of age, and literate (71.1%). The three most commonly stated occupation categories were (1) housewife; (2) agriculture, forestry, or fishery worker; and (3) student. Over one-half reported having had a previous eye examination. Presbyopia and low hyperopia were the predominant refractive conditions encountered. Over one-third of patients presented with visual acuities 6/15 (20/50) or worse, and one-third of this group had never had an eye examination. Three-quarters of the patients required prescription lenses and over 20% had cataract. The dispensing of presbyopic corrections to first time patients is clearly the most valuable service provided by the clinics. Teaming up with mobile cataract camps may improve the access to surgical care for patients with cataract. It is important that mobile vision projects target future efforts toward those likely to be missed by conventional screenings.

Adolescent↗
PubMed1996

Clinical vision characteristics of the congenital achromatopsias. I. Visual acuity, refractive error, and binocular status.

Visual acuity, refractive error, and binocular status were determined in 43 autosomal recessive (AR) and 15 X-linked (XL) congenital achromats. The achromats were classified by color matching and spectral sensitivity data. Large interindividual variation in refractive error and visual acuity was present within each achromat group (complete AR, incomplete AR, and XL). However, the number of individuals with significant interocular acuity differences is very small. Most XLs are myopic; ARs show a wide range of refractive error from high myopia to high hyperopia. Acuity of the AR and XL groups was very similar. With-the-rule astigmatism of large amount is very common in achromats, particularly ARs. There is a close association between strabismus and interocular acuity differences in the ARs, with the fixating eye having better than average acuity. The large overlap of acuity and refractive error of XL and AR achromats suggests that these measures are less useful for differential diagnosis than generally indicated by the clinical literature.

Adolescent↗
PubMed1997

The artifact of retinoscopy revisited: comparison of refractive error measured by retinoscopy and visual evoked potential in the rat.

PURPOSE: The validity of retinoscopy in small eyes has not been clearly established due to uncertainty regarding the source of the ocular reflections assessed during this procedure. A widely cited model which proposes that their origin is the inner limiting membrane of the retina was evaluated in the rat by comparing refractive errors measured by retinoscopy to those measured by visual evoked potentials (VEPs). METHODS: Ten rats were refracted both by cycloplegic streak retinoscopy and by VEP while viewing 0.05 to 0.15 cpd square-wave gratings-reversed at 1.875 Hz. Spherical aberration of the rat eye was assessed as a potentially confounding variable in VEP refraction by sequential retinoscopic refractions across the rat's natural pupil through a 1.5-mm pinhole. RESULTS: All animals were moderately to highly hyperopic by both methods (range = +4.5 to +18.5 D). Spherical aberration was minimal (median = 3.5 D of overcorrected aberration). The median difference between retinoscopic refractions and those by VEP was not significant (+1.94 D more hyperopia by retinoscopy; p = 0.062, Wilcoxon signed rank) but was significantly less than the +9.64 D difference predicted by an inner limiting membrane model (upper 95% limit = +3.76 D). CONCLUSION: This suggests that the origin of the retinoscopic reflex is located in the outer retina rather than at the inner limiting membrane. Correction factors for retinoscopy in small eyes may be smaller than previously assumed.

Animals↗
PubMed1999

Afocal magnification does not influence chick eye development.

In defocus-induced ametropia experiments, retinal blur circles are a likely source of information as to the magnitude but not the sign of the defocus. However, magnification (and minification) produced by the lenses may be a cue. In this study, 1-day-old broiler chicks (N = 13) were treated monocularly for 7 days with special goggles containing approximately afocal iseikonic lenses which were designed to produce 10% retinal image magnification. This is a little less than the magnification produced by +10 D defocusing lenses used to produce about 10 D of hyperopia in earlier work. Intraocular dimensions of both eyes were measured by A-scan ultrasonography on the first and last day. Refractive states of both eyes were measured daily with a retinoscope and trial lenses. After the birds were sacrificed, the eyes were enucleated, weighed, and measured with calipers. Before the treatment there was no difference in the refractive state or dimensions of the right and left eyes. After 1 week of goggle wear there was still no significant difference between the eyes in spite of the magnification produced by the goggles. These data suggest that factors other than magnification are responsible for the ability of the eye to respond to the sign of defocus.

Accommodation, Ocular↗
PubMed1999

Imposed retinal image size changes--do they provide a cue to the sign of lens-induced defocus in chick?

BACKGROUND: Young chicks can adjust their eye growth to compensate for both imposed hyperopia and myopia (using negative and positive spectacle lenses); the rate of eye elongation increases in the former and slows in the latter case. This emmetropizing behavior implies that the eye can distinguish the sign and magnitude of defocus, although the identity of the cue(s) involved is unknown. As the spectacle lenses used in these studies generally introduce significant retinal image size differences that are in opposite directions for negative and positive lenses (minification vs. magnification), we asked whether retinal image size might provide the required sign information. METHODS: This question was addressed by manipulating retinal image size while keeping lens power constant. We also investigated the effect of eliminating other potential cues, accommodation and chromatic aberration, under these conditions. Three negative "size" lenses of approximately -11 D optical power were used, with 2 of the lenses producing magnification rather than minification as typical of negative lenses (i.e. +1.9% and +6.9% compared to -2.9%). The lenses were fitted monocularly to 7-day-old chicks, which were subsequently measured at 9 and 11 days of age (refractive error and axial dimensions). The same lens-wearing schedule was applied to two other groups of chicks that had monocular ciliary nerve section surgery to prevent accommodation 2 days posthatching; one of these groups was reared under monochromatic yellow light instead of white light. RESULTS: Near-perfect refractive compensation was seen by the end of the treatment period with all three lenses, for all three treatment groups, and there was also little difference in the rate of compensation among the various groups. In all cases, the typical responses of axial (mainly vitreous chamber) elongation and myopia were observed. CONCLUSIONS: That manipulations to retinal image size, which either decrease or reverse the usual effects of negative lenses, did not disrupt compensation to the imposed hyperopic defocus, even in the absence of accommodation and chromatic aberration cues, argues against imposed retinal image size changes being the directional cue to defocus in experimental emmetropization.

Accommodation, Ocular↗
PubMed1999

Effects of muscarinic cholinergic receptor antagonists on postnatal eye growth of rhesus monkeys.

PURPOSE: To study a potential role for muscarinic receptors in the inhibition of deprivation-induced excessive axial elongation and myopia in a monkey model. METHODS: The right eyes of 20 newborn rhesus monkeys were occluded with a black contact lens. In seven monkeys each, either atropine or pirenzepine was topically applied daily to the occluded eyes. The nonoccluded fellow eyes and both the occluded and nonoccluded fellow eyes of another six monkeys were treated with vehicle solution. RESULTS: After 33 to 39 weeks, in 5 monkeys of the vehicle group, occluded eyes were longer and the myopic shift significantly greater than in the nonoccluded fellow eyes. In six atropine-treated monkeys, axial length and reduction of the initial hyperopia of occluded and nonoccluded fellow eyes were not different statistically. The myopic shift of the occluded eyes was significantly smaller than in the vehicle-treated occluded eyes. In the pirenzepine-treated group, axial length of the occluded eyes was similar to the nonoccluded eyes of controls and the occluded eyes of atropine-treated monkeys. There was a trend of pirenzepine to reduce the myopic shift of the occluded eye. No effect of atropine or pirenzepine was noted on muscarinic receptor density in retina, brain, or heart, but a small increase was observed in iris + ciliary body. CONCLUSIONS: The drug treatment results implicate muscarinic receptors in postnatal eye growth regulation. Because of interanimal differences our data do not indicate whether nonselective or selective muscarinic blockade is more effective in reducing deprivation-induced myopia.

Animals↗
PubMed2001

Comparison of refractive state and circumferential morphology of retina, choroid, and sclera in chick models of experimentally induced ametropia.

PURPOSE: Simultaneous comparisons of the circumferential morphological tissue profiles and final refractions from form-deprivation myopia (FDM), defocus-induced myopia (DIM), and defocus-induced hyperopia (DIH) models of ametropia have been made to test the hypothesis that changes in the thickness profiles of the three coats of the eye, and particularly that of the choroid, can be predicted from the degree of induced refractive error. METHODS: Hatchling chickens (n = 23) were raised for 2 weeks wearing either a monocular translucent diffuser (FDM, n = 8), monocular -10.00 D lens goggle (DIM, n = 7), monocular +10.00 D lens goggle (DIH, n = 7), or nothing (Norm, n = 1). All animals were refracted using retinoscopy and were then sacrificed, and whole eyes were processed for scanning electron microscopy. Retinal, choroidal, and cartilaginous sclera (CS) thickness measurements were made from photographic collages of the entire circumference of the globe. Of the 23 chickens, complete morphological profile data were available for both eyes of 10 animals (nine treated and one normal). The contralateral fellow eyes (FEyes) of all nine experimental chickens were used as experimental controls as paired comparisons for statistical analyses. RESULTS: Morphological profiles of control and experimental eyes revealed significant systematic regional variations in tissue thickness. This variation was related to nasal or temporal eccentricity with the nasal side generally thinner than the temporal. Retinal, choroidal, and CS tissue from FDM and DIM eyes showed very similar anatomical responses despite significantly different degrees of refractive change. DIH eyes showed significant increases in choroidal thickness but none in retinal or CS thickness. Analysis of fellow control eyes indicated that in both myopia models (FDM and DIM), significant changes in all tissues of the untreated fellow eyes occur whereas only the choroid of the fellow eye was affected in the hyperopic (DIH) model. CONCLUSIONS: The morphological similarity observed in the circumferential profiles of the retina, choroid, and cartilaginous sclera of the FDM and DIM eyes despite approximately 20 D difference in final refraction suggests that choroidal thickness is not a good predictor of final refractive error across models. Similarly, the final refractive difference of approximately 20 D between the DIM and the DIH eyes did not receive a major contribution from the final difference in choroidal thickness (with its implied effect on vitreous chamber length).

Animals↗
PubMed2001

Acquired unilateral visual loss attributed to an accommodative spasm.

BACKGROUND: Accommodative spasm (AS) has been reported to be a rare cause of an acquired unilateral visual loss. We describe a unique case of acquired visual loss due to an apparent unilateral AS triggered by occlusion of the contralateral eye. Clinical examination and photorefraction techniques were performed during the acute phase of the disorder and in the follow-up evaluations. CASE REPORT: An otherwise healthy 27-year-old woman presented with a 2-month decrease of vision in her left eye. Unaided visual acuity in the right eye was 20/20 and in the left eye was finger counting. Orthophoria existed at distance and near. The decrease in vision in the left eye was attributed to an apparent unilateral AS of 5 D, which occurred only when the right eye was occluded. Under the occluder, the right eye also manifested an AS. With the left eye occluded or with binocular viewing, the right eye and left eye accommodated normally. With a 5 D convex lens before the right eye, the visual acuity in the left eye was 20/20. Refractive error with cycloplegia revealed low hyperopia in each eye. CONCLUSION: AS can be the cause of acquired unilateral visual loss. To our knowledge, this is the first documented report of an apparent unilateral AS triggered by occlusion of the contralateral eye.

Accommodation, Ocular↗