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PubMed1996

The selective effect of optical defocus on detection and resolution acuity in peripheral vision.

Detection and resolution acuity was measured at 30 degrees in the periphery for sinusoidal gratings under differing amounts of optical defocus. Within the range -2.0 to +2.5 diopters defocus, detection acuity was higher than resolution acuity. As defocus increased, detection acuity decreased continuously but resolution acuity was little affected until around 2.0 diopters defocus. The results indicate that resolution performance is sampling limited in peripheral vision, even for significant refractive error, and is more robust than detection acuity to the effects of optical defocus.

Humans↗

PubMed1996

Triple vs nonsimultaneous procedures in Fuchs' dystrophy and cataract.

OBJECTIVES: To determine the outcome and refractive status after triple and nonsimultaneous procedures for Fuchs' endothelial dystrophy and cataract. DESIGN: Records of 236 patients with Fuchs' endothelial dystrophy who were examined during 1988 were reviewed retrospectively. SUBJECTS: Group 1 consisted of 93 patients who had triple procedures (penetrating keratoplasty, extracapsular cataract extraction, and posterior chamber intraocular lens implantation); group 2 consisted of 32 patients who had nonsimultaneous procedures (penetrating keratoplasty followed by extracapsular cataract extraction and posterior chamber intraocular lens implantation). Variables in the first eye that had surgery for each patient were compared between the groups by means of unpaired t tests and Fisher's exact test. RESULTS: Mean follow-up after undergoing transplantation was 6 years in group 1 and 8 years in group 2. Clear grafts were obtained in 89 (96%) of eyes of group 1 and in 29 (91%) of eyes in group 2 (P = .37). A best-corrected visual acuity of 20/40 or better was achieved in 60 (65%) of eyes in group 1 and in 21 (66%) of eyes in group 2. Refractive errors within 2 diopters of emmetropia were found in 37 (42%) of eyes in group 1 and in 15 (48%) of eyes in group 2 (P = .51). Mean refractive cylinder was 3.9 diopters in group 1 and 4.1 diopters in group 2 (P = .67). CONCLUSIONS: There was no statistically significant difference in the outcome and refractive status after triple and nonsimultaneous procedures. To avoid increased cost and delay in visual rehabilitation, we recommend a triple procedure for patients with Fuchs' endothelial dystrophy and visually significant cataracts.

Aged↗

PubMed1989

Clinical indications for intraocular lens power calculation: a prospective randomised study.

Patients about to undergo cataract extraction were assessed clinically using several criteria to try and judge the necessity for biometry. The patients judged not to need biometry were allocated randomly to two groups, one of which had biometry. The only significant clinical criterion for biometry was found to be the wearing of glasses since before the age of 30 years. Several unexpectedly high refractive errors occurred in the group of patients who did not have biometry. In the group of patients judged not to need biometry but allocated to the biometry group, refractive results were significantly better (nearer to target refractions) than in the unmeasured group. Routine pre-operative biometry is probably the only way to avoid unexpected high ametropia, and it also improves the refractive results. There is however much room for improvement in the accuracy of biometry.

Age Factors↗

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↗

PubMed2000

Twenty-five years of contact lenses: the impact on the cornea and ophthalmic practice.

PURPOSE: The history of contact lenses has occurred in the latter half of the 20th century. In particular, events in the 1970s through the 1980s related to the invention of soft, hydrogel contact lenses have revolutionized the contact lens industry and the eye care attached to it. This article recounts that history from the perspective of market forces, inventions, and discoveries about the physiologic functioning of the cornea. METHODS: The relevant literature is critically reviewed. RESULTS: Discoveries about the oxygen needs of the cornea and consumer pressure for clear, comfortable, around-the-clock vision have resulted in a history of rigid gas permeable and soft lenses that leads to today's contact lens picture. The short-term and long-term effects of chronic hypoxia and the levels of lens oxygen transmissibility necessary to avoid them have been well-described. The advent of the soft lens, followed by the "human experiment" with initial extended-wear modalities, led to the advent of the disposable soft contact lens. CONCLUSIONS: In the past 25 years, the development and wide acceptance of soft contact lenses have revolutionized the management of refractive error and corneal diseases.

Contact Lenses↗

PubMed2003

Prevalence of undetected ocular conditions in a pilot sample of school children.

Parents of 134 children (age 5-18 years; 84% participation) attending a private school gave informed consent for their child's participation in a pilot study to demonstrate the feasibility and estimate sample size for a larger study of myopia prevalence, the Sydney Myopia Study. LogMAR visual acuity and other ocular assessments, including cycloplegic autorefraction (tropicamide 1%) and examination of the media and fundus, were performed. The prevalence of significant ocular conditions was 28.2%. Eleven children (8.4%) wore glasses. Five were referred for a change in their correction. Previously undetected ocular conditions (19.8%) included one child with ocular pathology and four children with strabismus. Uncorrected refractive error (16.8%) was the most common reason for referral and was more predominant in the senior students (25%), corresponding with an age-related shift in mean spherical equivalent refraction towards myopia (less than 7 years: +0.40 +/- 0.60 D; more than 15 years: -1.15 +/- 1.18 D). Three senior students were classified as having socially significant correctable vision impairment. These findings suggest that reliance on ad hoc referrals could result in delayed referral and that vision screening in both early and later school years may be desirable.

Adolescent↗

PubMedDate not supplied

Laser epithelial keratomileusis with mitomycin C: indications and limits.

PURPOSE: To assess the advantages and safety of using mitomycin C (MMC) with laser epithelial keratomileusis (LASEK) by measuring high order aberrations of the cornea. METHODS: We analyzed the results of 86 eyes that had LASEK plus a brushstroke of MMC 0.01%. Another group of 100 eyes had LASEK only (control group). Mean follow-up was 312 days for the MMC group and 774 days for the control group. A Nidek EC-5000 laser was used in all eyes. We measured mean refractive error, best spectacle-corrected visual acuity (BSCVA), haze, and high order aberrations before and at 1 month and nearly 1 year after LASEK. RESULTS: Mean baseline spherical equivalent refraction was -6.80 +/- 3.00 D for the MMC group and -6.00 +/- 3.10 D for the control group (P=.34). In eyes with low myopia (-1.20 to -10.80 D), a single ablation zone of 6 mm with a transition zone of 8 mm was used, and in the higher myopia group (-5.60 to -15.50 D), smoothing and a cross sphere procedure (+0.75 D) were used. Mean spherical equivalent refraction after LASEK for low myopia in the MMC group at last examination (mean follow-up 312 days) was +0.50 +/- 0.93, and 0 +/- 0.34 D for the control group. Mean spherical equivalent refraction after LASEK for high myopia in the MMC group at last examination (mean follow-up 312 days) was +0.50 +/- 1.03 D, and +0.40 +/- 0.78 D for the control group. Mean haze in the low myopia MMC group was 0.06 and in the control group, 0.11; in the high myopia MMC group it was 0.1, and in the control group, 0.27 (all differences P<.05). No differences between baseline and postoperative BSCVA were noted. Early and late overcorrection were noted in the MMC group. Increased high order aberrations were evident at 1 month and 1 year in the MMC groups. CONCLUSIONS: The use of mitomycin C 0.01% with LASEK significantly decreased subepithelial haze. However, refractive outcome was less predictable. High order aberrations increased after LASEK with MMC. Additional studies with longer follow-up are necessary to evaluate long-term effects, and ideal MMC concentration and exposure time.

Antibiotics, Antineoplastic↗

PubMed2003

[Complications after laser refractive surgery].

The laser refractive surgery is very effective method of refractive errors correction. The method is very popular, but serious complications may occur and the visual acuity may decrease. In this article authors show the possible complications after the laser refractive procedures.

Corneal Diseases↗

PubMed2005

Accuracy of accommodation in heterophoric patients: testing an interaction model in a large clinical sample.

A model of the cross-link interactions between accommodation and convergence predicted that heterophoria can induce large accommodation errors (Schor, Ophthalmic Physiol. Opt. 1999;19:134-150). In 99 consecutive patients with intermittent tropia or decompensated phoria, we tested these interactions by comparing their accommodative responses to a 2.50-D target under binocular fused conditions (BFC) and monocular occluded conditions (MOC). The accommodative response in BFC frequently differed from that in MOC. The magnitude of the accommodative errors in BFC, ranging from an accommodative lag of 1.80 D (in an esophoric patient) to an accommodative lead of 1.56 D (in an exophoric patient), was correlated with distance heterophoria and uncorrected refractive errors. These results indicate that heterophoria affects the accuracy of accommodation to various degrees, as the model predicted, and that an accommodative error larger than the depth of focus of the eye occurs in exchange for binocular single vision in some heterophoric patients.

Accommodation, Ocular↗

PubMed2005

Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster.

PURPOSE: To compare the accuracy of biometry using conventional A-scan ultrasonography and partial coherence interferometry, and to improve the accuracy of biometry by sequential audit of postoperative refractive error. METHODS: The study was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using both A-scan ultrasonography and the Zeiss IOLMaster (ZIOLM). A single experienced optometrist refracted all patients 2 weeks after surgery. The errors between expected and achieved refraction were calculated and compared between the two methods. In phases 2 and 3, a further 22 and 20 patients, respectively, were recruited and only the ZIOLM was used for biometry. The manufacturer's suggested A-constant was refined and the error between expected and achieved refraction was calculated. RESULTS: In phase 1, the median unexpected error for the ZIOLM was+0.63 (interquartile range+0.368 to+1.015) and for A-scan biometry was --0.24 (interquartile range--1.335 to+0.802). In phase 1 65% of patients' postoperative refractions were found to be within 1.0 D of emmetropia using the ZIOLM (55% using A-scan biometry). Refinements to the A-constant improved this to 95% by phase 3. CONCLUSION: An error was identified in IOL power estimation with the ZIOLM, when using the manufacturer's recommended A-constant (recommended and previously optimized ultrasound A-constant 118.0; ZIOLM optimized A-constant 118.6). Serial modifications to the A-constant were successful in reducing the unexpected error to well within the tolerance limits of published international standards.

Adolescent↗

PubMed2005

Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster.

PURPOSE: To compare the accuracy of biometry using conventional A-scan ultrasonography and partial coherence interferometry, and to improve the accuracy of biometry by sequential audit of postoperative refractive error. METHODS: The study was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using both A-scan ultrasonography and the Zeiss IOLMaster (ZIOLM). A single experienced optometrist refracted all patients 2 weeks after surgery. The errors between expected and achieved refraction were calculated and compared between the two methods. In phases 2 and 3, a further 22 and 20 patients, respectively, were recruited and only the ZIOLM was used for biometry. The manufacturer's suggested A-constant was refined and the error between expected and achieved refraction was calculated. RESULTS: In phase 1, the median unexpected error for the ZIOLM was +0.63 (interquartile range +0.368 to +1.015) and for A-scan biometry was - 0.24 (interquartile range - 1.335 to +0.802). In phase 1 65% of patients' postoperative refractions were found to be within 1.0 D of emmetropia using the ZIOLM (55% using A-scan biometry). Refinements to the A-constant improved this to 95% by phase 3. CONCLUSION: An error was identified in IOL power estimation with the ZIOLM, when using the manufacturer's recommended A-constant (recommended and previously optimized ultrasound A-constant 118.0; ZIOLM optimized A-constant 118.6). Serial modifications to the A-constant were successful in reducing the unexpected error to well within the tolerance limits of published international standards.

Adolescent↗

PubMed2005

Influence of age on peripheral refraction.

To investigate how age affects peripheral refraction we measured objective peripheral refraction for 55 young subjects (24+/-4 years) and 41 older subjects (59+/-3 years) out to 35 degrees eccentricity in temporal and nasal visual fields. Subjects were compared in 1D subgroups based on central spherical equivalent refractions (low hypermetropes +0.54 D to +1.51 D, emmetropes +0.50 D to -0.49 D, low myopes -0.50 D to -1.49 D, moderate myopes -1.50 D to -2.58 D). Overall, young and older subjects with similar refractive corrections had similar peripheral refraction components. Both age groups showed relative hypermetropic shifts in the peripheral fields as myopia increased and also decreases in peripheral astigmatism J180 as myopia increased. J45 varied little across the visual field with linear relationships occurring between J45 and visual field angle for all but one subgroup (older emmetropes). Peripheral refraction in emmetropes to moderate myopes is relatively unaffected by age for healthy eyes of similar refractive errors.

Adult↗

PubMed1985

An intraocular lens power calculator for the IBM PC and PCjr computers using input variable selection.

A BASIC program to calculate intraocular lens power and refractive errors using previously derived equations is presented. The program was written for the IBM PC and PCjr computers with an emphasis on clinical usefulness. Program features include a comparison of refractive and axial length predictions of secondary implant power and velocity compensation for axial length measurements made on aphakic patients. Equation specification by input variable selection and automatic averaging of keratometer readings make the program highly efficient.

Computers↗

PubMed1996

VDU work: longitudinal survey on refractive defects.

A longitudinal survey in two different phases with an interval of 4 years (including more than 23,000 employees) has been carried out to study whether the time spent using VDU (daily hours and years of work) can change the refractive state. With reference to the whole sample including all refractions, there was no significant difference in the refractive state in employees who spent varying daily hours or years working at VDU. Furthermore, there were no significant changes in the refractive states of emmetropic, hypermetropic and myopic subjects, with regard to the time spent working at VDU. The data have shown that a high exposure to VDU work (more than 6 h per day or more than 6 years spent working at a VDU) is not responsible for inducing or worsening refractive error.

Adult↗

PubMedDate not supplied

Visual acuity in monocular pediatric aphakia: does epikeratophakia facilitate occlusion therapy in children intolerant of contact lens or spectacle wear?

Twenty-two children had a monocular cataract extracted between 1981 and 1986. Twelve of these patients eventually tolerated a monocular contact lens or anisometropic spectacle wear. Eleven patients initially would not tolerate conventional therapy, and epikeratophakia was performed. Of the 12 patients tolerating a contact lens or spectacles, eight (67%) now see 20/60 or better, and six (50%) see 20/40 or better. Only one (10%) of the patients maintaining the epikeratophakia graft developed vision as good as 20/70. Epikeratophakia did not facilitate occlusion therapy for amblyopia. The critical factor in the development of good vision following monocular cataract extraction was the patient's willingness to patch the better eye, not the method of correcting the refractive error.

Aphakia, Postcataract↗

PubMed1990

Learning curve for radial keratotomy.

I prospectively evaluated my own learning curve for radial keratotomy (RK) by comparing the results achieved in two groups: 20 consecutive eyes on which I performed RK without having had previous experience with the procedure (group 1); and 20 other eyes, matched for age, sex, and preoperative refractive error, on which I performed RK after I had performed the procedure 250 times (group 2). Although there were nine microperforations in group 1 and none in group 2, the postoperative refractions and uncorrected visual acuities were similar in both groups. Since the microperforations had no adverse effect on the visual results, it is reasonable to conclude that there was, in effect, no learning curve involved in my experience with RK.

Adult↗

PubMed2004

[Childhood refraction: epidemiology, progression, evaluation and a method for correcting ametropia].

Children's refraction and its progression are important because refractive errors can be precisely corrected. Some types of simple ametropia can generate reversible perturbations after optical correction and others are amblyogenic and strabogenic ametropia. Definition, epidemiology (frequency and risk factors), progression of refraction, evaluation and an optical correction method are described.

Child↗

PubMed2025

Causal association between different types of ametropia and risk of diabetic retinopathy: a two-sample Mendelian randomization study.

OBJECTIVE: To investigate the causal link between ametropia and diabetic retinopathy, as well as to offer genetic support for the association between these two conditions. METHODS: This study employed a methodology involving the utilisation of genome-wide association studies data that are publicly accessible. Specifically, single nucleotide polymorphisms (SNPs) that exhibit a strong association with ametropia were employed as instrumental variables, and a two-sample Mendelian randomization (MR) approach was employed to examine the causal relationship between different types of ametropia and diabetic retinopathy. The main findings were derived from the utilisation of inverse variance weighted (IVW), while supplementary results were obtained through the utilisation of MR Egger, weighted median, simple mode and weighted mode. Additionally, a sensitivity analysis was conducted using the 'leave-one-out' method. Cochran's Q statistics were also used to quantify the heterogeneity of SNPs. RESULTS: 38 SNPs were finally included. The results of the IVW analysis indicate that myopia may exert an inhibitory effect on the development of diabetic retinopathy (OR=0.596, 95% CI (0.371, 0.957), p<0.05). Conversely, hypermetropia (OR=8.882, 95% CI (0.389×10-3, 2.06×105), p>0.05) and astigmatism (OR=1.004, 95% CI (0.888, 1.135), p>0.05) do not exhibit a causal relationship with the risk of diabetic retinopathy. CONCLUSION: This two-sample Mendelian randomization study provides evidence that myopia may impede diabetic retinopathy occurrence, while hypermetropia and astigmatism show no significant causal effects. However, our analysis treats refractive errors as independent entities, which may not reflect their clinical interdependence. Further investigations are warranted to elucidate myopia's protective mechanisms.

Humans↗