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PubMed2001

Pulsatile ocular blood flow study: decreases in exudative age related macular degeneration.

BACKGROUND: Pulsatile ocular blood flow (POBF) is a parameter for evaluating choroidal blood flow. POBF in the patients with non-exudative and exudative age related macular degeneration (AMD) was investigated. METHODS: POBF, pulse amplitude (PA), systolic and diastolic blood pressures, intraocular pressure (IOP), refractive error, and axial length were compared among 10 patients with non-exudative AMD, 11 patients with exudative AMD, and 69 age matched controls. A Langham OBF computerised tonometer was used with the participants in the sitting position to measure POBF and PA. RESULTS: No significant differences were found in age, systolic and diastolic blood pressures, IOP, or refractive error between patients with exudative and non-exudative AMD and the control subjects. In the patients with exudative AMD the POBF (median, 372.7 microl/min) and PA (median, 1.2 mm Hg) were significantly lower than in the patients with non-exudative AMD (median, 607.0 microl/min (p = 0.02) and 2.2 mm Hg (p = 0.04), respectively) and control subjects (median, 547.4 microl/min (p = 0.01) and 2.0 mm Hg (p = 0.01), respectively). CONCLUSIONS: These data show that the POBF and PA in the patients with exudative AMD are lower than in the patients with non-exudative AMD and normal subjects. Decreased choroidal blood flow may have a role in the development of choroidal neovascularisation in AMD.

Aged↗
PubMed2005

[Phacoemulsification and the negative power of intraocluar lenses in extremely myopic eyes].

OBJECTIVE: To evaluate the clinical effects of phacoemulsification and the negative power of intraocluar lens implantation in patients with extreme myopia and cataract. METHODS: 89 patients (126 eyes) received phacoemulsification and a negative power intraocluar lens implantation. Preoperative axial length, postoperative visual acuity and refractive error were recorded. Intraoperative and postoperative complications were observed. The follow-up time is from 6 to 25 months. RESULTS: The mean preoperative axial length is 32.45 mm. Best corrected visual acuity achieved 0.2 or better in 106 eyes (84.1%) and 0.5 or better in 69 eyes (54.8%). Of the 126 eyes, 56.3% were within 1.00 diopter (D) of refractive error and 90.5% were within an error of 2.00 D. Only 1 eye has posterior capsule rupture. 28 eyes had binocular disturbances. 15 eyes developed posterior capsule opacification and 6 eyes were performed neodymium: YAG laser posterior capsulotomy. No retinal or choroidal detachment or pressure improvement was seen during the follow-up. CONCLUSION: It is safe and effective for extreme myopia with cataract to implant a negative power intraocular lens after phacoemulsification.

Adult↗
PubMed1997

Severe myopia as a risk factor for progressive visual field loss in primary open-angle glaucoma.

The optic nerve head in severely myopic eyes may be particularly vulnerable to glaucomatous damage. To study this hypothesis, we examined 122 primary open-angle glaucoma eyes with fair to good control of the intraocular pressure and a sign of baseline optic nerve damage. Then, parameters for the progression of the visual field defects were evaluated by multivariate analysis. A high mean intraocular pressure (p = 0.007) and a large refractive error (p = 0.023) were significant risk factors for subsequent visual field loss. A high baseline cup-to-disk ratio (p = 0.100) was a marginal risk factor. Nonsignificant parameters included patient age (p = 0.692), the use of beta-adrenergic antagonists (p = 0.384), gender (p = 0.831) and left versus right side (p = 0.977). When the refractive error was used to subclassify patients into severely myopic (< or = -4 dpt), mildly myopic (-0.25 to -4 dpt), or emmetropic and hyperopic (> or = 0 dpt), only severe myopia was a significant risk factor for progressive visual field loss. Severe myopia, but not mild myopia, is a significant risk factor for subsequent visual field loss in patients with primary open-angle glaucoma.

Adolescent↗
PubMed2004

[Anisometropia and stereopsis].

PURPOSE: To examine the amount of defect of stereopsis in experimentally induced anisometropia of various value and type. MATERIAL AND METHODS: 20 healthy adults without significant refraction error or anisometropia and with full stereopsis were examined. They all undergone Titmus stereotest (circles) after they had experimentally induced anisometropia with the use of trial lenses. Mean values of stereopsis in arc sec. were calculated for each value of anisometropia. RESULTS: The largest defect of stereopsis was noted in spherical hypermetropia. In all kinds of refraction error the critical value for almost complete loss of stereopsis was 3D plus. Generally, the same values of anisometropia in sphere result in slightly more severe loss of stereopsis than in cylinder.

Adult↗
PubMed2006

Wavefront-guided enhancements using the wavelight excimer laser in symptomatic eyes previously treated with LASIK.

PURPOSE: To describe our clinical experience in wavefront-guided LASIK enhancements using the WaveLight ALLEGRETTO system (WaveLight Technologie AG, Erlangen, Germany) for symptomatic eyes previously treated with standard LASIK. METHODS: Twenty-six eyes of 20 patients with residual myopia, hyperopia, or mixed astigmatism and/or night vision symptoms after primary standard LASIK were considered for wavefront-guided customized retreatment using the WaveLight ALLEGRETTO WAVE 200 Hz excimer laser system (model 106). Preoperative best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity, topography with the ALLEGRETTO Topolyzer, wavefront analysis using the ALLEGRETTO WAVE Tscherning Analyzer, and contrast sensitivity were compared to postoperative (enhancement) measurements. RESULTS: Twenty-two of the original 26 eyes underwent wavefront-guided enhancement, 4 were excluded because they did not meet wavefront-guided treatment inclusion guidelines of this study. Mean follow-up was 8 months (range: 6 to 13 months, standard deviation [SD] 2). All patients were within +/- 0.50 diopters (manifest refraction) of intended postoperative refraction. The mean preoperative BSCVA improved from 20/25 (SD +/- 0.12) to 20/18 (SD +/- 0.1) postoperatively. All patients gained at least one line of BSCVA, and a maximum of three lines. There was no loss of BSCVA in any patient. The total amount of high order aberrations (RMSH) decreased from an average of 1.04 (SD +/- 0.22) to 0.46 (SD +/- 0.14) microm. Patients also had a mean improvement in low contrast sensitivity of 59%. CONCLUSIONS: Based on this small series, customized wavefront-guided enhancements using the WaveLight ALLEGRETTO system in patients who underwent previous LASIK appear to be safe and effective in correcting residual refractive error, reducing high order aberrations, and improving visual symptoms when reliable and reproducible measurements are achieved.

Cornea↗
PubMed2002

[Three-dimensionnal representation and descriptive geometry of the pure spherical and pure cylindrical profiles of Excimer photoablation].

PURPOSE: To analyze the theoretical shape of the lenticules of corneal tissue ablated using Excimer laser for the correction of pure negative and positive spherical and cylindrical refractive errors, and to investigate the possible correlations between their spatial configuration and the clinical outcome for each procedure. METHODS: To obtain a theoretical three-dimensional representation of each ablated lenticule, we used software that performs boolean operations on three-dimensional virtual surfaces (Bryce 3D, Metacreation, Dublin, Ireland). The representation of the theoretical shape of the refractive lenticule etched by a given profile of ablation based on a paraxial model over a circular optical zone was obtained by performing appropriate Boolean operations between different preoperative and postoperative surfaces or elements. These operations were repeated to obtain the representation of the theoretical additional lenticule corresponding to the volume of tissue ablated to blend any abrupt optical zone edges with a constant slope. RESULTS: The lenticule corresponding to the negative spherical treatment had its maximum thickness in its center and no thickness at its edge, thus inducing a natural blend with the peripheral untreated cornea. The lenticule corresponding to the positive spherical treatment had its maximal thickness at the junction between the optical and transition zones, which are both circular. The lenticule corresponding to the negative cylindrical treatment had its maximal thickness along the flatter initial meridian and an elliptical transition zone contour. The lenticule corresponding to the positive cylindrical treatment had its maximal thickness at the edge of the optical zone along the initial flatter meridian, and no thickness at the perpendicular principal meridian. The transition zone is also elliptical. CONCLUSION: The basic characteristics of the lenticule corresponding to the pure negative spherical treatment could explain the lesser degree of postoperative refractive regression than that one occurring after pure positive spherical treatment and pure positive and negative cylindrical treatments. The characteristics of the lenticules corresponding to the negative and positive cylindrical treatments may also account for the substantial spherocylindrical coupling and regression, respectively commonly observed after such treatments. The three-dimensional representation of the lenticules ablated for the correction of pure spherical and cylindrical refractive errors may help to better understand the outcome of these procedures aimed at reshaping the anterior surface of the cornea.

Algorithms↗
PubMed1987

Experimentally induced myopia does not affect post-hatching development of the chick lens.

Myopia, as characterized by a large refractive error (e.g. -10.7 +/- 0.4 D), was induced in post-hatch chicks by a 14 day application of a goggle that was designed to blur the retinal image. In comparison to untreated eyes, the treated eye showed significant changes in wet eye weight and both axial and equatorial lengths. However, the lenses of myopic and non-myopic eyes were not significantly different in focal characteristics, light transmittance or total soluble protein content. Thus the lens neither contributes to, nor compensates for the large refractive error observed in experimentally induced myopia.

Animals↗
PubMed1999

Prevalence of myopia in Sherpa and Tibetan children in Nepal.

BACKGROUND: Tibetan and Sherpa children living in Nepal share a common ancestry in Tibet and areas to the north of Nepal, but it is evident that these people experience widely contrasting educational and environmental conditions. The purpose of this study was to compare the prevalence of myopia in children with similar genetic backgrounds but who are exposed to contrasting environments. METHODS: Unaided vision and refractive error was measured in 555 Tibetan children in Kathmandu and 270 Sherpa children in the Solu Khumbu region of Nepal. RESULTS: There were marked differences in vision and the prevalence of myopia in the two groups. Ninety-two percent of the Sherpa children had Snellen vision of 20/22 (0.89) or better compared with 70% of the Tibetan children. The range of refractive errors was -6.50 to +7.00 D for the Tibetan children and -1.00 to +3.50 D for the Sherpa children. The Sherpa children had a prevalence of myopia of 2.9% compared with 21.7% for the Tibetan children. CONCLUSIONS: The prevalence of myopia in Sherpa children is low and their rural lifestyle appears to be relatively unstressed. Tibetan children have a higher prevalence of myopia and more rigorous schooling. We did not establish a causal relationship between myopia and the type of schooling, or the environment in general, but we did demonstrate that a simple, rural lifestyle is at least compatible with a virtual absence of myopia.

Adolescent↗
PubMed1995

[Excimer laser photorefractive keratectomy in myopia and astigmatism--1 year experience].

The authors evaluate the results of photorefractive keratectomy by means of an excimer laser myopia and astigmatism in 343 eyes with a minimal follow-up period of 9 months. The value of the preoperative refractive error expressed in spherical equivalents was -1,75 to -18,5 d. In astigmatism the maximal value was -5 cyl. d. The group was divided into four sub-groups: A) -1,75 to -3,0 d., B) -3,25 to -6,0 d., C) -6,25 to -10,0 d., D) more than -10,25 d. The spherical equivalent of the refractive error 9 month after operation was -0,28 d. in group A, -0,37 d. in group B, -0,67 d. in group C and -1,82 d. in group D. Uncorrected vision, 6/12 or better, 9 mons after operation was recorded in group A in 98,1% patients, group B 95,6% group C 91,2% and in group D in 72,5% patients. The authors proved a high effectiveness, safety predictability and stability of photorefractive keratectomy by means of an excimer laser in myopia up to -10 d. Photorefractive keratectomy is a promising method which extends the possibilities of correcting myopia and astigmatism in sufficiently positively motivated and indicated patients.

Adult↗
PubMed1996

Myopia associated with hyperbaric oxygen therapy.

BACKGROUND: Hyperbaric oxygen therapy (HBOT) involves exposing patients to elevated oxygen pressures and concentrations for the treatment of soft tissue degenerative diseases. As side effects, some patients experience cataract development and/or a significant increase in myopia. SUBJECTS: Eight subjects participated in this project. All were receiving HBOT for health problems. METHODS: For all subjects, acuities and refractive error corrections were measured before and after HBOT sessions at the beginning, midpoint, and end of therapy. For four subjects, A-scan ultrasound and corneal curvature measurements were also made before and after selected HBOT sessions. In addition, susceptibility to free radical damage and indicators of actual damage were measured by blood analyses. During the first half of HBOT therapy, four subjects took placebo tablets; during the second half, antioxidant supplements were given. RESULTS: No subject showed significant acuity or refractive error changes produced by single HBOT sessions. Two of the 8 subjects showed significant increases in myopia over the 20 session course of HBOT. No corresponding changes were found in the ultrasound, corneal curvature, or blood analysis data. DISCUSSION: Theoretically, the increases in myopia could have been caused by lenticular refractive index changes resulting from oxidative damage to lens proteins. However, the biochemical assays used in this project did not predict which subjects were susceptible to increased myopia, nor did they demonstrate elevated levels of free radical activity in a subject who did experience an increase in myopia.

Adult↗
PubMed2004

Prevalence of ocular diagnoses found on screening 1539 adults with intellectual disabilities.

OBJECTIVE: To study the prevalence of ocular disorders in adults with intellectual disabilities (IDs) in the Netherlands. DESIGN: Cross-sectional survey. SUBJECTS: A stratified random sample (for age more than 50 years and Down syndrome [DS]) of 1598 participants drawn from a base population of 9012 adult users of ID services with mild to profound intellectual disabilities in the Netherlands. METHODS: Participants underwent on-site visual screening on the basis of a protocol. Results were related to degree of ID, occurrence of DS, age, and a diagnosis of visual impairment or blindness. Referral to ophthalmologists followed when visual impairment was diagnosed. MAIN OUTCOME MEASURES: Diagnosis of ocular disorders and their prevalence. RESULTS: Refractive errors were most prevalent (60.6%), followed by strabismus (44.1%) and lens opacities (18.1%). Besides these, in participants diagnosed as visually impaired, cerebral visual impairment was the most common untreatable disorder (12.6%), followed by macular degeneration (5.4%). Compared with known figures from general populations, the prevalence of ocular diagnoses in adults with ID was significantly higher. The occurrence of refractive errors and strabismus was significantly related to DS (odds ratio [OR], 2.16; 95% confidence interval [CI], 1.56 to 3.00; and OR, 2.47; 95% CI, 1.93 to 3.17, respectively). Lens opacities had an independent relation with age more than 50 years (OR, 4.23; 95% CI, 3.04 to 5.88) and DS (OR, 8.27; 95% CI, 5.95 to 11.49). Keratoconus was independently related to DS (OR, 7.65; 95% CI, 3.91 to 14.96) and degree of ID (OR, 5.56; 95% CI, 2.79 to 11.06). Corneal opacities also were related to DS (OR, 2.70; 95% CI, 1.41 to 5.18) and degree of ID (OR, 5.53; 95% CI, 2.66 to 11.48). The risk of ocular hypertension was increased by age more than 50 years (OR, 2.54; 95% CI, 1.16 to 5.57) and severe or profound ID (OR, 4.86; 95% CI, 2.06 to 10.63); DS decreased the risk (OR, 0.21; 95% CI, 0.05 to 0.94). CONCLUSIONS: In 1539 adults with ID in the Netherlands, high prevalences of ocular disorders were found. Adults with ID in general have an increased risk of severe myopia, strabismus, and lens opacities; DS, older age, or severe ID further increase the risk of specific ocular disorders.

Adult↗
PubMed2000

Estimate and measure of the region of view and myopia resulting from vitreous gas.

PURPOSE: After vitreous gas injection, patients notice better acuity in downward gaze than in horizontal gaze. The authors evaluated the refractive error and the size of the region within which vision improves. METHODS: For the vitreous fluid-gas interface, the authors calculated the angle of total internal reflection and the expected myopic shift and then measured them in nine consecutive patients. The volume of gas, declination angle at which perception of small targets occurred, and preoperative and postoperative refractive error in downward gaze were measured. RESULTS: Total internal reflection occurs at 41.5 degrees declination. Patients perceived a region of improved acuity below 41 degrees (+/-5 degrees) declination. The difference between the calculated and clinically measured gas-induced myopia was less than 25% for five of nine patients. The largest measured induced myopia was -23.9 diopters (60% gas volume). In eight eyes, patients read 5-point type or smaller. CONCLUSIONS: Patients accurately perceive that their acuity improves in downward gaze; the boundary of this region corresponds with the angle of total internal reflection. Calculations predict that vitreous gas produces a myopic shift and aberration. These data support the notion that ocular positioning by patients with vitreous gas can be enhanced by instructing them to regard near targets in downward gaze.

Gases↗
PubMed2005

[Calculation of the IOL power with the numerical simulation program].

PURPOSE: Realisation of a numerical simulation program for the optic system of human eye. Simulation of the refractive errors and their correction with optic system. Calculation of the IOL power with this program. METHOD: The program is accomplished in Pascal programming language. RESULTS: Applying the formulas derived from Abbe's invariant we can calculate all the paraxial characteristics of human eye. With this program we can calculate the power of an air lens, of a contact lens and power of an IOL. CONCLUSIONS: This program simulate the optic system and refractive errors of the human eye. Its necessary to know all the parameters of the optic system of the eye to calculate the power of an IOL. This program can be used in an educational and research purposes.

Algorithms↗
PubMed2003

Childhood blindness in India: a population based perspective.

AIM: To estimate the prevalence and causes of blindness in children in the southern Indian state of Andhra Pradesh. METHODS: These data were obtained as part of two population based studies in which 6935 children <or=15 years of age participated. Blindness was defined as presenting distance visual acuity <6/60 in the better eye. RESULTS: The prevalence of childhood blindness was 0.17% (95% confidence interval 0.09 to 0.30). Treatable refractive error caused 33.3% of the blindness, followed by 16.6% due to preventable causes (8.3% each due to vitamin A deficiency and amblyopia after cataract surgery). The major causes of the remaining blindness included congenital eye anomalies (16.7%) and retinal degeneration (16.7%). CONCLUSION: In the context of Vision 2020, the priorities for action to reduce childhood blindness in India are refractive error, cataract related amblyopia, and corneal diseases.

Adolescent↗
PubMed2005

The effect of common reductions in letter size and contrast on accommodation responses in young adult myopes and emmetropes.

PURPOSE: Accommodation errors during reading and the subsequent near work-induced transient myopia (NITM) that occurs have been implicated in the development and progression of myopia. This study investigated the effects of two letter variables, size and contrast, on accommodation accuracy during the near task and on NITM and its subsequent decay. These were varied so as to mimic what might occur when students photocopy and reduce reading materials. METHODS: Based on their refractive errors, young adult subjects (18-25 years) were classified into three groups: emmetropes (n = 19), stable myopes (n = 17), and progressing myopes (n = 17). Three print sizes (N4, N6, and N8) and two print contrasts (90% and 60%) were used to give six different reading targets. Targets were presented in random order at 25 cm (4 D demand) and the text read for comprehension for 3 minutes. For each target, accommodation accuracy and NITM and its decay were measured using the free space Shin-Nippon SRW-5000 autorefractor. RESULTS: When data for all subjects were pooled, there was a significant effect of letter size (p = 0.030) but not contrast (p = 0.898) on accommodation accuracy; however, differences were small and unlikely to be clinically relevant. NITM (p = 0.033) and its decay (p = 0.012) also varied with letter size. NITM was greater and decay longer for larger letters. We found no effect of refractive error group on accommodation accuracy. In contrast, there was a significant difference in the magnitude of NITM and its decay for emmetropic and myopic subjects (although no effect of progression status); myopes had larger NITM values and longer decay times to baseline than emmetropes (NITM myopes: 0.37 +/- 0.14D vs. emmetropes: 0.19 +/- 0.17 D, p = 0.005; decay time myopes: 15.12 +/- 6.58 seconds vs. emmetropes 7.10 +/- 4.82 seconds, p = 0.0045). The differences in NITM and its decay between the two refractive groups were of similar magnitude for all six combinations of letter size and contrast. CONCLUSIONS: Our data do not support the suggestion that common reductions in letter size or contrast of reading material (as might occur for photocopied reading materials) cause greater accommodation inaccuracy and greater near work-induced adaptation effects that would exacerbate myopia development in young adults.

Accommodation, Ocular↗
PubMed2003

The effects of overnight orthokeratology lens wear on corneal thickness.

PURPOSE: To investigate corneal thickness changes during overnight orthokeratology with reverse-geometry rigid gas-permeable (RGP) contact lenses worn over a 3-month period. METHODS: Eighteen young adult subjects with low myopia (<or=4.00 D) were fitted with reverse-geometry lenses (BE; UltraVision Pty. Ltd., Brisbane, Queensland, Australia), which were worn for 3 months on an overnight basis and were removed during the day. Another 10 subjects were fitted with conventional RGP lenses (J-Contour; UltraVision) that were worn for 1 month in the right eye on a similar wearing schedule; the left eye acted as a non-lens-wearing control. Refractive error was recorded in the morning and evening, and total, epithelial, and stromal corneal thicknesses were measured across the horizontal meridian with an optical pachometer. RESULTS: The orthokeratology group showed significant reductions in myopia (+1.66 +/- 0.50 D; P < 0.001) from day 1, which stabilized by day 10. Central corneal thinning (-9.3 +/- 5.3 microm, P < 0.001), which was epithelial in origin, was found from day 1; central stromal change was negligible. Midperipheral corneal thickening, which was stromal in origin, was confirmed by day 4 (+10.9 +/- 5.9 microm, P < 0.001). No change was found in peripheral corneal thickness. Analysis of day-90 data by Munnerlyn's formula indicated that corneal sagittal height change resulting from the thickness changes could account for the refractive effect. In the conventional RGP group, there were no significant changes in refractive error or corneal thickness. CONCLUSIONS: Overnight orthokeratology causes rapid central corneal epithelial thinning and midperipheral stromal thickening. The consequent change in corneal sagittal height is the primary factor underlying the refractive effect of orthokeratology.

Adult↗
PubMed1982

Prospective clinical study of radial keratotomy.

A prospective clinical study of radial keratotomy was conducted at the University of Maryland. Results of surgery on 33 eyes of 19 patients with a minimum follow-up of seven months and a mean of 13.8 months are reported. There were eight patients (15 eyes) who needed adequate unaided visual acuity for occupational purposes. Preoperative visual acuity was 20/400 in 79% of eyes. Postoperative visual acuity was 20/50 or better in 48% of cases. However, in patients with preoperative refractive errors of 5 diopters or less, postoperative visual acuity was 20/50 or better in 84% of cases. Average decrease in myopia was 2.5 diopters. Decrease in myopia following radial keratotomy did not correlate with corneal curvature or whether 8 or 16 incision technique was used. However, there was a very significant (P = 0.001) difference in postoperative visual acuity of patients with refractive error of 5 diopters or less, as compared to those with greater than 5 diopters of myopia. Complications included corneal scarring, vascularization, and glare. No microperforation or endothelial cell loss was observed.

Adolescent↗
PubMed1997

Prevalence of general binocular dysfunctions in a population of university students.

PURPOSE: Although some authors report that the prevalence of general binocular dysfunctions (nonstrabismic) for nonpresbyopes in the clinical population is greater than any condition except refractive error, limited research is available to support this statement. This clinical study determined the presence and clinical implications of these conditions in a population of university students with heavy near visual demands. METHODS: From a group of second year students who were given a thorough eye examination, 65 students were selected. The criteria for selection were the absence of significant uncorrected refractive error, healthy eyes, and no strabismus or amblyopia. RESULTS: 32.3% of the subjects showed general binocular dysfunctions. In 10.8% of the cases, accommodative excess was present. 7.7% had convergence insufficiency with accommodative excess. 6.2% showed accommodative insufficiency. 3.1% had basic exophoria. Convergence excess with accommodative insufficiency, basic esophoria, and fusional vergence dysfunction all showed the same prevalence of 1.5%. CONCLUSIONS: Accommodative and nonstrabismic binocular vision problems are prevalent in this population. Accommodative excess is the most common condition. Because these dysfunctions may have a negative effect on performance, appropriate vision evaluation for this population is important.

Accommodation, Ocular↗