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PubMed1995

Longitudinal evidence of crystalline lens thinning in children.

PURPOSE: Most earlier studies indicated that the eye's crystalline lens grows continually throughout life, but cross-sectional results of crystalline lens thinning during childhood have been reported. The authors investigated crystalline lens thickness in childhood using cross-sectional and longitudinal data. METHODS: The Orinda Longitudinal Study of Myopia is a community-based study of normal eye growth and myopia development in school-age children. During a 1-to 3-year period, A-scan ultrasonographic lens thickness measurements of 869 children 6 through 14 years of age were analyzed. RESULTS: On average, between the ages of 6 and 10 years, the crystalline lens thins in its axial dimension by almost 0.2 mm. This thinning can be depicted by a cubic model. In this sample, the children with myopia had thinner crystalline lenses than the children with emmetropia of the same age. CONCLUSIONS: This article provides the first longitudinal evidence that the crystalline lens thins during the period of coordinated ocular growth between the ages of 6 and 10 years. Further, it shows that lens thickness is associated with refractive error. Thinner crystalline lenses in children with myopia may result from one of two underlying mechanisms: Either the crystalline lens exhausts its ability to compensate for axial elongation after undergoing accelerated lens thinning before the onset of myopia, or the crystalline lens in the myopic eye may be thinner throughout childhood, during which it thins at a rate consistent with other refractive errors. If mechanical forces link eye growth to crystalline lens compensation, more complex, visually guided feedback loops may not be needed to explain the normal eye growth that results in emmetropization.

Adolescent↗

PubMed2002

Theoretical analysis of peripheral imaging after excimer laser corneal refractive surgery for myopia.

PURPOSE: To explore theoretically the retinal point images in the peripheral fields of eyes that have had excimer laser refractive surgery. University research laboratory. METHODS: Model eyes were based on Navarro's finite schematic eye, the eyes being made myopic by an increase in axial length. To simulate photorefractive keratectomy (PRK), the anterior shape and thickness of the cornea were modified. Variables included pupil size, ablation zone size, preexisting refractive error, and the addition of a blending zone. Image-quality criteria for each retinal point image were its size and the angular separation of the centroids of those parts of the image produced by rays passing through ablated and unablated corneal zones. RESULTS: In the peripheral visual field, the boundary between the ablated and unablated cornea caused a separation of the retinal image of a single point into 2 parts. The separation increased with the preexisting refractive error. Image quality was correspondingly reduced by ablation. As pupil size increased, the field angle at which the retinal image doubling first occurred decreased. Increasing the diameter of the ablation zone or using a blending zone increased the angle at which the doubling first occurred, and the blending zone improved image quality considerably. Chromatic effects appeared to be relatively unimportant. CONCLUSIONS: This analysis provides further evidence of the disadvantages of small central ablation zones in excimer laser refractive surgery and of the advantages of well-designed blending zones in improving postsurgical peripheral image quality. Image quality in the peripheral field of the pseudoemmetropic post-PRK eye is generally worse than in a naturally emmetropic eye, even though the axial image quality may be similar.

Humans↗

PubMedDate not supplied

Topography-controlled excimer laser photorefractive keratectomy.

PURPOSE: To assess whether photorefractive keratectomy (PRK) controlled by videokeratography can successfully treat refractive errors in eyes with corneal irregularities and improve spectacle-corrected visual acuity. METHODS: In a prospective clinical study, PRK was performed in 10 eyes of 10 patients. Reason for surgery was irregular astigmatism after penetrating keratoplasty, corneal irregularity after corneal scarring, corneal astigmatism in keratoconus, and decentration after myopic and hyperopic PRK. Excimer ablation was controlled by preoperative videokeratography (Orbscan II, Orbtek) using the MEL-70 system from Aesculap Meditec. Follow-up was 6 months. RESULTS: Concerning manifest refraction, the sphere was reduced on average from +1.92 to +0.57 D, 6 months postoperatively. Cylinder changed from -1.95 D on average to -0.30 D at 6 months postoperatively. There was improvement of uncorrected visual acuity of 2 or more lines in 5 eyes and no change in 5 eyes 6 months postoperatively. Spectacle-corrected visual acuity improved in 2 eyes by 2 to 3 lines, in 9 eyes by 1 to 3 lines, and showed no change in 1 eye. CONCLUSION: Videokeratography-controlled PRK improved refractive errors in irregular corneas with improvement of spectacle-corrected visual acuity.

Adult↗

PubMed2003

Comparison of reverse-geometry lens designs for overnight orthokeratology.

PURPOSE: The efficacy of overnight wear of four types of reverse-geometry lenses was compared. The length of time needed to achieve correction and any adverse events that occurred during the course of the study were recorded. METHODS: In this prospective, randomized study, 60 subjects (18 to 35 years old) with refractive error between -1.00 to -4.00 D (cyl </= -1.50) wore reverse-geometry lenses overnight only. All subjects were assigned a Rinehart Reeves lens in one eye, and subsets of 20 subjects were randomly assigned a Mountford BE, DreimLens, or Contex D Series 4 lens for the contralateral eye. Visits included baseline, dispensing, 1 day, 1 week, and 1 month. Biomicroscopy, unaided visual acuity, subjective refraction, best-corrected visual acuity at high and low contrast and high and low illumination, corneal topography, and subjective rating data were collected. RESULTS: Forty-six subjects completed the study. At 1 month, there were no significant differences between lens types in their effect on unaided visual acuity, subjective sphere, subjective cylinder, best-corrected visual acuity at high and low contrast at high illumination and low contrast at low illumination, apical corneal radius, corneal eccentricity, and subjective ratings. Between 1 week and 1 month, there was a significant improvement in subjective ratings of quality of day and night vision (p < 0.05) but no significant change in the objective measures. No significant ocular adverse events were observed during the trial. CONCLUSIONS: The lens types tested were all similarly effective in the reduction of myopic refractive error. Subjective ratings continued to improve after objective measures stabilized at 1 week. Overnight lens wear proceeded for 1 month without significant adverse reactions.

Adult↗

PubMed2000

Effects of experimentally induced ametropia on the morphology and optical quality of the avian crystalline lens.

PURPOSE: To examine the effects of refractive error on avian lens morphology and optical quality. METHODS: Hatchling white leghorn chicks were unilaterally goggled for 7 days with either a form-deprivation goggle (n = 12), a -10 D defocus goggle (n = 12), or a +10 D defocus goggle (n = 12) to induce myopia and hyperopia. Optical quality of lenses (focal length and focal length variability) from treated and contralateral control eyes was assessed using a scanning laser apparatus. Lens morphology was examined by light and electron microscopy. RESULTS: Although the induction of refractive errors did not significantly alter lens size, shape, paraxial focal length, or average focal length, average focal length variability increased. Lenses from eyes goggled with form-deprivation and +10 D defocus goggles demonstrated a twofold increase in average focal length variability, when compared with their contralateral controls. The morphology of the lens is not altered by these experimental manipulations. CONCLUSIONS: This study provides evidence that the refractive development of the chick lens is not independent of the refractive development of the ocular globe and that chick lenticular development is influenced by both genetics and visual experience.

Animals↗

PubMed1995

A dynamic relationship between myopia and blur-driven accommodation in school-aged children.

Previously we reported that recently myopic children accommodated insufficiently to blur induced by negative lenses. The purpose of the present study was to relate changes in blur-driven accommodation to myopia development in children. Refractive errors and the accommodation response function (ARF) were measured in 23 myopic and 40 emmetropic children on two occasions separated by periods ranging from 6 to 12 months. Repeated measures of accommodation were made with a Canon R-1 autorefractor while negative lenses of increasing power were placed in front of the child's right eye viewing 20/100 letters at 4 m. Concomitant changes in refractive error and in accommodative function over periods of 6-12 months were found to be highly correlated in myopes (r = 0.77) but not in emmetropes (r = 0.09).

Accommodation, Ocular↗

PubMed2004

Subjective assessment of mesopic visual function after laser in situ keratomileusis.

The authors' study evaluated subjective reports of mesopic visual function after LASIK for spherical and spherocylindrical myopia and evaluated whether age, pupil size, treatment amount, residual postoperative refractive error, or other factors correlated with subjective findings. Preoperative, 3-month, and 6-month subjective patient questionnaires were administered. Results for questions about glare with night driving and glare with bright lights were tallied and evaluated using standard statistical methods. The results indicated that subjective reports of mesopic visual function after myopia LASIK improve overall. Worsened symptoms are most likely to occur in eyes with poor refractive outcomes. Correction of residual refractive errors may improve night driving and glare symptoms after LASIK.

Adolescent↗

PubMed1991

Contact lenses and refractive surgery. Addressing patient problems and concerns.

Contact lenses, used by millions of people throughout the United States, are a safe, effective way to correct refractive errors and to improve the vision of patients with diseased corneas. Proper care and cleaning of contact lenses is very important; at the first sign of eye irritation, the lenses should be removed and a physician should be consulted. New advances include improved gas-permeable materials, new hypoallergenic solutions, and planned replacement systems. Excimer laser treatment and radial keratotomy are more invasive methods of correcting refractive problems and must be approached with great care and caution.

Contact Lenses↗

PubMed1990

[Color vision defects in chronic open angle glaucoma].

Glaucomatous optic nerve atrophy is associated with morphological and psychophysical changes. Using Roth's Besancon anomalometer, the Farnsworth 100 hue test and Nagel's anomaloscope, we examined color vision in 86 eyes of 51 patients suffering from chronic open-angle glaucoma and 57 eyes of 41 normal subjects. In the normal control group, blue und green sensitivity decreased and, accordingly, the anomaly quotient tested with Nagel's anomaloscope increased significantly (p less than 0.00001) with age. If the glaucoma and control groups were matched for age, refractive error and central visual acuity, decreasing blue sensitivity significantly (p less than 0.05) correlated with diminished visibility of the retinal nerve fiber bundles, a higher morphological glaucoma stage and larger perimetric defects. The presence and depth of localized defects of the retinal nerve fiber layer were not significantly different in glaucoma subgroups with lower and higher blue sensitivity, respectively, when the subgroups were matched for age, refractive error and visual acuity. No papillomorphologic marker for the cyanodyschromatopsia was detected. Red-green color vision was not significantly different between the normal and glaucoma eyes. Testing of blue color vision as an additional method is useful in the differential diagnosis of beginning glaucomatous optic nerve damage in patients with clear optic media and lack of macular changes.

Adult↗

PubMed1990

Subretinal hemorrhages with or without choroidal neovascularization in the maculas of patients with pathologic myopia.

We examined 20 patients (24 eyes) who had refractive errors of -8 diopters or more and subretinal hemorrhages at the initial visit. They were divided into two groups according to fluorescein angiographic findings: 15 eyes without choroidal neovascularization (CNV) and 9 eyes with CNV. Subretinal hemorrhage without CNV was frequent in patients aged 20-39 years (mean, 36.8 years). CNV was common in patients aged 60-79 years (mean, 61.0 years). No relationship was noted between refractive error and type of hemorrhage. In the eyes without CNV, the subretinal hemorrhages disappeared spontaneously after a few months. The visual acuity of these patients was variable at the initial visit (range, 0.01-0.8), and was unchanged or improved during the follow-up period. In the eyes with CNV, the visual acuity was less than 0.1 at the initial visit and was unchanged or worse during the follow-up period.

Adult↗

PubMed1999

Ocular components values and their intercorrelations in Saudi Arabians.

There are no previous studies on the dimensions of ocular components and their intercorrelations in adult Saudi Arabians. In this study ocular components were measured by ultrasonography and keratometry in 152 adult Saudis. Their ages ranged from 16 to 50 years. The males had significantly longer anterior chamber depth (ACD), vitreous chamber depth (VCD), axial length (AL) and axial length/corneal radius ratio (AL/CR) than females. However, females had non-significantly steeper corneas than males. The AL/CR ratio had the highest correlation with refractive error. Corneal radius of curvature was positively correlated with VCD and AL. Lens thickness was negatively correlated with the VCD, AL and AL/CR ratio. Myopes had significantly deeper ACD, VCD, and higher AL/CR ratio than nonmyopes. Myopes had significantly thinner lenses than hyperopes. The average values of the optical components and their intercorrelations are similar to reported values obtained from subjects of other races but with comparable refractive errors.

Adolescent↗

PubMed2003

Photorefractive keratectomy to correct hyperopic shift after radial keratotomy.

To evaluate the safety, efficacy, and predictability of photorefractive keratectomy (PRK) to correct post-radial-keratotomy (RK) hyperopic shift. University of Sherbrooke, Sherbrooke, Québec, Canada.This retrospective nonconsecutive case series comprised 53 eyes of 53 patients who had PRK to correct hyperopic shift after RK. Both RK and PRK were performed by the same surgeon at the same clinic from 1993 to 2001.The mean time after RK was 57 months (range 24 to 84 months). The mean follow-up after hyperopic PRK (HPRK) was 10 months (range 3 to 33 months). The mean hyperopic shift 1 month post-RK to HPRK was +1.6 diopters (D) +/- 1.0 (SD) (range +0.25 to +4.125 D). The mean pre-HPRK spherical equivalent (SE) was +2.15 +/- 0.80 D (range +1.00 to +4.125 D) and the mean post-HPRK SE, -0.10 +/- 0.80 D (range -2.00 to +2.125 D). At the last examination, 47 eyes (88.7%) had a refractive error within +/-1.0 D of emmetropia and 38 eyes (71.7%) had an uncorrected visual acuity of 20/25 or better. Two eyes lost 1 Snellen line of best corrected visual acuity. No significant haze or complications developed in any eye. Hyperopic PRK with a conservative technique (large optical zone and small ablation thickness) can be used successfully to correct RK-induced hyperopia in patients with small to moderate refractive errors. It appeared to be effective, predictable, and safe.

Adult↗

PubMed2000

[Ocular findings associated with hypertelorism].

PURPOSE: To show that in hypertelorism (a horizontal orbital dystopia in which interorbital distance is increased) there are various ophthalmologic abnormalities associated: strabismus, nystagmus, amblyopia, refractive errors, palpebral malpositions, lacrimal system imperforation, fundoscopic and anterior segment lesions. We want to show that the frequence and severity of ophthalmic findings are associated to the severity of hypertelorism. But the evolution and treatment of ocular findings is independent from the treatment of this orbital dystopia. METHODS: We have studied 12 cases of hypertelorism. We made a previous ophthalmologic examination which included: visual acuity, ocular motility, cycloplegic refraction, palpebral statics, lacrimal system, slit lamp and fundoscopic examination. All four walls of each orbit are osteotomized to free them from the frontal, zygomatic, maxillary, nasal and sphenoid bones in surgical correction of hypertelorism. RESULTS: Amblyopia and strabismus appeared in 58.3% of patients each of them, being exotropias the most common. The most frequent refractive error was hypermetropia (40%). Other ocular findings were: ptosis, lacrimal system impermeability, heterochromic iris, optic disk hypoplasia and enophthalmos. None of the deffects was modified after surgical correction of hypertelorism. CONCLUSIONS: Ophthalmologic findings associated with hypertelorism are not caused by the deformity. They are more frequent as higher the severity of the hypertelorism is. The ocular findings do not modify after surgical treatment of hypertelorism, except if we treat them specifically.

Adolescent↗

PubMed2002

[LASEK--new laser refractive surgical technique. Personal experience].

PURPOSE: The purpose of this study was to evaluate the clinical results of refractive error correction LASEK. MATERIAL AND METHODS: 115 eyes were analyzed after LASEK. The eyes were divided into 4 groups (myopia, myopic astigmatism, hyperopia, hyperopic astigmatism). The follow-up has taken 3 months. The effectiveness of this method was evaluated on the basis of the best visual acuity without correction after LASEK procedure, compared to the best visual acuity with correction before LASEK. The course of the healing process, the state of cornea and subjective symptoms were also evaluated. RESULTS: After 2 weeks in whole group the mean UCVA was in the same range of values compared with the BCVA before the operation. There were no postoperative complications observed. CONCLUSION: On the basis of our own observations we can say that LASEK is an effective and safe method for correction of refractive errors.

Follow-Up Studies↗

PubMed2002

The Hong Kong progressive lens myopia control study: study design and main findings.

PURPOSE: To determine whether the use of progressive addition spectacle lenses reduced the progression of myopia, over a 2-year period, in Hong Kong children between the ages of 7 and 10.5 years. METHODS: A clinical trial was carried out to compare the progression in myopia in a treatment group of 138 (121 retained) subjects wearing progressive lenses (PAL; add +1.50 D) and in a control group of 160 (133 retained) subjects wearing single vision lenses (SV). The research design was masked with random allocation to groups. Primary measurements outcomes were spherical equivalent refractive error and axial length (both measured using a cycloplegic agent). RESULTS: There were no statistically significant differences between the PAL and the SV groups for of any of the baseline outcome measures. After 2 years there had been statistically significant increases in myopia and axial length in both groups; however, there was no difference in the increases that occurred between the two groups. CONCLUSIONS: The research design used resulted in matched treatment and control groups. There was no evidence that progression of myopia was retarded by wearing progressive addition lenses, either in terms of refractive error or axial length.

Child↗

PubMed2006

No apparent association between ocular perfusion pressure and visual field damage in normal-tension glaucoma patients.

PURPOSE: To investigate the correlation of ocular perfusion pressure (OPP) with general and localized visual field damage in normal-tension glaucoma (NTG) patients. METHODS: Correlations between OPP, blood pressure, age, intraocular pressure, refractive error, and extent of visual field damage in the eye with the worst mean deviation (MD) were investigated retrospectively in 94 eyes of 94 NTG patients. Visual fields were analyzed statistically with respect to 15 sectors between two age-matched groups of subjects with high or low OPP. RESULTS: Significant positive correlations were found between OPP and age (P < 0.001), blood pressure and age (P < 0.05), and MD and refractive error (P < 0.01). OPP had no significant correlation with MD or mean sensitivity in the visual field in any of the visual field sectors. CONCLUSION: OPP and systemic blood pressure have no evident effect on the extent or pattern of visual field damage in NTG.

Adolescent↗

PubMed1999

Visual acuity screening versus noncycloplegic autorefraction screening for astigmatism in Native American preschool children.

INTRODUCTION: Visual acuity screening (VAS) is less reliable in preschoolers than in school-aged children as a means of detecting significant refractive error. We wished to compare the effectiveness of VAS with the effectiveness of an objective method, noncycloplegic autorefraction screening (NCARS), in detecting the presence of significant astigmatism warranting spectacle correction. METHODS: We examined 245 Native American Head Start registrants aged 3 to 5 years. We attempted to obtain uncorrected visual acuity using Lea Symbols logMAR Chart (Precision Vision Inc, Villa Park, Ill), noncycloplegic autorefraction using the Nikon Retinomax K-plus (Nikon Corp, Melville, NY), and cycloplegic refraction (CR) on each eye. The VAS failure criterion was either a 2-line acuity difference between eyes or acuity worse than 20/40 in either eye. The NCARS and CR failure criterion was the spectacle correction threshold exceeding the 50th percentile on the basis of a survey of AAPOS members. RESULTS: We completed VAS in 96% of children and NCARS and CR in 100% of children. There was high prevalence (31%) of significant astigmatic refractive error in this sample. Ten subjects who did not permit bilateral visual acuity measurements were scored as having a positive test result. The sensitivity and specificity of VAS were 90% and 44%, respectively. NCARS had sensitivity and specificity of 91% and 86%, respectively. NCARS becomes cost-effective after 1044 children are screened, assuming that the cost of the autorefractor is 300 times the cost of the referral examination. CONCLUSION: VAS offers high sensitivity but suffers from poor specificity. NCARS greatly reduces the number of unnecessary referrals. In this population, NCARS becomes cost-effective after approximately 1000 children are screened.

Arizona↗

PubMed1992

Myopia following penetrating keratoplasty for keratoconus.

The frequent occurrence of spherical myopia after penetrating keratoplasty for keratoconus is partly the result of the excessive dioptric power of the grafted cornea which occurs when the diameter selected for the donor button is greater than the diameter of the host incision. This excessive power could be reduced by eliminating disparity between the diameters of the graft and host. To determine what proportion of the myopia in these eyes would persist as a result of axial myopia the axial lengths of 60 patients grafted for keratoconus and 25 emmetropic controls were compared. A keratometry, objective refraction, and contact probe ultrasonic biometry were performed on all eyes. A comparison of the results with a representational schematic eye indicated that the mean spherical refractive error of the grafted keratoconic eyes (-4.83 dioptres) was the combined effect of steepness of the corneal graft (mean radius of curvature 7.46 mm) and an abnormally great axial length (mean 24.84 mm). The increased axial length was mainly the result of elongation of the posterior segment of the globe with a small contribution from an increased anterior chamber depth. Though axial myopia is common in keratoconus, a further study of 70 keratoconic eyes that had not been grafted showed no statistically significant correlation between the posterior segment length and the severity of corneal ectasia. These data suggest that even if excessive corneal power is eliminated after penetrating keratoplasty for keratoconus the associated axial myopia would still produce a mean spherical refractive error of at least -2.8 dioptres.

Adult↗