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PubMed1999

Recent advances in refractive surgery.

Refractive errors are some of the most common ophthalmic abnormalities world-wide and are associated with significant morbidity. Tremendous advances in treating refractive errors have occurred over the past 20 years. The arrival of the excimer laser has allowed a level of accuracy in modifying the cornea that was unattainable before. Although refractive surgery is generally safe and effective, it does carry some risks. Careful patient selection, meticulous surgical technique and frequent follow-up can avoid most complications. The experience of a surgical team can also affect the outcome and the incidence of complications. The future should bring continued improvement in outcomes, fewer complications and exciting new options for treating refractive errors.

Humans↗
PubMedDate not supplied

Intracorneal ring segments after laser in situ keratomileusis.

PURPOSE: To evaluate the safety and efficacy of intracorneal ring segments (ICRS) for correction of residual refractive error in patients previously operated with laser in situ keratomileusis (LASIK). METHODS: Thirteen postoperative LASIK eyes (eight patients) with residual myopic refractive error underwent implantation with INTACS (Keravision) intracorneal ring segments. Correction of the residual error was the first goal, but also improved best spectacle-corrected visual acuity was obtained by correcting residual irregular astigmatism. RESULTS: Mean spherical equivalent refraction improved from -3.25 to +0.75 D and mean uncorrected visual acuity improved from 0.2 to 0.6 after ICRS insertion. Best spectacle-corrected visual acuity remained stable or improved; no eyes lost lines of corrected visual acuity. In one of the 13 eyes, the intracorneal ring segments were removed because of progressive stromal melting. CONCLUSIONS: The use of corneal ring segments in selected eyes with residual myopic refractive errors after LASIK was safe and effective.

Adult↗
PubMed1983

Discriminant analysis of acquired esotropia surgery. Predictor variables for short- and long-term outcomes.

In a retrospective study, a computer-based stepwise discriminant analysis was used to create a biostatistical model of the results of surgery in acquired esotropia. One hundred seventy-two patients who had bilateral medial rectus muscle recession as an initial operative procedure with at least 6 months postoperative follow-up were studied. The outcome groups for the discriminant analysis were based on the ocular deviation 6 weeks after the first surgery and at the patient's last visit, or the presence or absence of stereopsis at the last visit. With respect to the two predominant ocular deviation groups (Esotropia or Success) 6 weeks after surgery, 11 independent variables were analyzed; those determined to be prognostic of the outcome grouping were refractive error of the left eye and preoperative deviation, in that order. With respect to ocular deviation at last visit, 146 patients were followed for over 2 years and were last examined when over 5 years of age; of the 12 independent variables analyzed, postoperative deviation at 6 weeks, refractive error of the right eye, and age of onset were predictive. With respect to stereopsis, 126 patients had similar follow-up; of the 11 independent variables analyzed, only postoperative deviation at 6 weeks was prognostic. The results indicate that in patients with acquired esotropia the postoperative deviation is the most important prognostic factor for both the maintenance of ocular alignment and the status of stereopsis; refractive error and the age of onset of the esotropia influence the ocular alignment at the last visit.

Age Factors↗
PubMed2001

Photographic reproduction of out-of-focus and distorted ocular imagery.

The necessary settings and parameters were determined for ordinary camera and lens systems to faithfully reproduce out-of-focus and distorted imagery as it falls upon the retina of the human eye. Theoretic considerations of both geometric and physical optics were used to calculate the "relative blur" and distortion produced by refractive error added to ordinary camera lenses as opposed to refractive error in an arbitrary thick-lens optical system bounded by air and fluid (i.e. the eye). In both the camera and the eye, "relative blur" was determined to be directly proportional to dioptric defocus and to aperture size, and effectively independent of the focal length. Distortion of imagery was also found to be independent of the focal length. Photographs corroborate the theoretic findings. A given amount of relative blur, however, appeared somewhat greater when recorded on photographic film than when appreciated by the human eye. The Stiles-Crawford effect, the chromatic aberration of the eye, and neural processing probably each contribute to this difference. Previous investigators have grossly exaggerated blur and distortion in photographs intended to simulate ocular imagery and have drawn misleading conclusions from their results.

Humans↗
PubMed2004

Prevalence of myopia in a group of Hong Kong microscopists.

PURPOSE: To study the prevalence and magnitude of myopia in a group of Hong Kong Chinese microscopists and compare it with that observed in microscopists working in the United Kingdom. METHODS: Forty-seven microscopists (36 women and 11 men) with a median age of 31 years and working in hospital laboratories throughout Hong Kong were recruited to the study. Information about past refractive corrections, microscopy work, and visual symptoms associated with microscope use were collected. All subjects had a comprehensive eye examination at The Hong Kong Polytechnic University Optometry Clinic, including measures of refractive error (both noncycloplegic and cycloplegic), binocular vision functions, and axial length. RESULTS: The prevalence of myopia in this group of microscopists was 87%, the mean (+/- SD) refractive error was -4.45 +/- 3.03 D and mean axial length was 25.13 +/- 1.52 mm. No correlation was found between refractive error and years spent working as a microscopist or number of hours per day spent performing microscopy. Subjects reporting myopia progression (N = 22) did not differ from the refractively stable group (N = 19) in terms of their microscopy working history, working hours, tonic accommodation level, or near phoria. However, the AC/A ratio of the progressing group was significantly greater than that of the stable group (4.59 delta/D cf. 3.34 delta/D). CONCLUSION: The myopia prevalence of Hong Kong Chinese microscopists was higher than that of microscopists in the United Kingdom (87% cf. 71%), as well as the Hong Kong general population (87% cf. 70%). The average amount of myopia was also higher in the Hong Kong Chinese microscopists than the Hong Kong general population (-4.45 D cf. -3.00 D). We have confirmed that the microscopy task may slightly exacerbate myopia development in Chinese people.

Adult↗
PubMedDate not supplied

Wavefront-guided ablation with Bausch and Lomb Zyoptix for retreatments after laser in situ keratomileusis for myopia.

PURPOSE: To evaluate the efficacy of wavefront-guided ablation for treatment of residual refractive error and higher order aberrations after laser in situ keratomileusis (LASIK) for myopia. METHODS: Twenty-one eyes of 13 patients with residual refractive error after myopic LASIK were treated with a wavefront-guided ablation with the Zyoptix technique. In 13 eyes of 8 patients (Group A) we lifted the flap with an epitheliorhexis technique; in 8 eyes of 5 patients (Group B) we cut a new flap with a Hansatome microkeratome. RESULTS: Preoperative root mean square (RMS) values were 1.370 for second order aberrations, 0.382 for total higher order aberrations, 0.273 for third order, 0.243 for fourth order, and 0.052 for fifth order aberrations. Three months postoperatively, RMS values decreased significantly to 0.278 (second order), 0.189 (total higher order), 0.138 (third order), 0.107 (fourth order), and 0.038 (fifth order). Ablation depth was two times greater than needed with a standard Planoscan treatment. Patients in the microkeratome recut group showed a trend toward overcorrection, and residual astigmatism was higher (-0.75 +/- 0.58 D) than in the flap lift group (-0.25 +/- 0.29 D). CONCLUSIONS: Wavefront-guided ablation was an effective method to correct residual refractive error and higher order aberrations after myopic LASIK. Functional and refractive outcomes were better when we lifted the flap than when we recut the flap.

Adult↗
PubMed1997

Comparison of intraocular lens computations using a neural network versus the Holladay formula.

PURPOSE: To compare the accuracy of intraocular lens (IOL) calculations using Holladay personalized calculations and a new method of trained neural networks. SETTING: A private ophthalmic practice. METHODS: We developed and trained a neural network to predict IOL powers using a personalized Holladay program and clinical data from 200 consecutive cases of one surgeon's results with one IOL. Clinical data included preoperative axial length, both keratometry values, anterior chamber depth, and human lens thickness. The neural network was trained to produce the actual postoperative refractive error, and the Holladay surgeon factor was continuously refined using the same results. After the network was successfully trained against the clinical data, it was used to compute IOL power in a double-masked study. Ninety-five patients were randomized between the Holladay personalized calculation and the neural network computation. There were no significant differences in age or preoperative refractive errors between the two groups. Manifest refractions were obtained during the masked period at least 6 weeks after surgery. RESULTS: Mean postoperative error from predicted refraction was +0.271 diopters (D) for the neural network group and -0.217 D for the Holladay personal group. Mean absolute error from predicted refraction was +0.63 D for the neural network group and +0.93 D for the Holladay personal group. There was a significant difference in postoperative refractive errors and mean absolute error between the two groups (P < .022; nonparametric Mann-Whitney test). An error of less than +/- 0.75 D was obtained by 72.5% of the neural network group and 50.0% of the Holladay group. CONCLUSIONS: The neural network prediction formula can improve IOL implantation calculations by tightening the variance of errors.

Cataract Extraction↗
PubMed2004

Ocular and nonocular findings in patients with aniridia.

BACKGROUND: Aniridia typically appears as a familial condition with autosomal dominant inheritance but can present as an isolated disease or sporadically in association with several syndromes. In this report we describe the various ocular manifestations of aniridia as well as the association of familial aniridia with two different ocular and systemic abnormalities present across three generations in two different families. METHODS: Descriptive case series of 33 patients (66 eyes) with aniridia. A full eye examination was performed at the beginning of the study, including past medical history, family history and type of inheritance, assessment for fixation pattern and presence of nystagmus, visual acuity testing, refraction, slit-lamp examination, gonioscopy, fundus examination with pupil dilation and anterior segment photography; additional glaucoma testing was done if the patient had high intraocular pressure. Patients were followed for at least 2 years. The interval between follow-up visits, which included gonioscopy and fundus examination with pupil dilation, depended on the findings in each case. A urology consultation was requested in all sporadic aniridia cases; consultations in psychiatry and gynecology were requested on the basis of the medical history or clinical suspicion during the ophthalmologic examination. RESULTS: Ten patients (30%) had sporadic aniridia, with no previous family history; Wilms' tumour did not develop in any of them during the follow-up period. In the autosomal dominant group, ocular and systemic findings present in combination with aniridia were observed in 20 patients in the two families. Family I had aniridia and developmental delay or behavioural disorders in three generations as well as high myopia (greater than 6.00 dioptres) in all affected adults. Family 2 presented a wide phenotypic variability of aniridia with myopia in three generations. Open-angle glaucoma developed in three young adults in this family, and two members were found to have gynecologic abnormalities (hypoplastic uterus and imperforate vagina). Myopia was the most prevalent refractive error (64%) in the 33 patients. Refractive correction significantly improved the visual acuity in half of these cases. Glaucoma was present in 10 patients (30%) and was the main cause of vision loss, provoking blindness in two cases (6%). Affected patients manifested progressive angle closure or presented with open-angle glaucoma. INTERPRETATION: Ophthalmologists should consider aniridia in patients with unusual iris malformations. Examination of family members may be key in making the diagnosis. Any refractive error should be corrected, as this may improve vision. All aniridic patients should be screened regularly for glaucoma, as this condition may occur at any age and can lead to permanent vision loss. Systemic and ocular associations should be considered as they may present in combination with anirida. In our series, developmental delay or behavioural disorders and myopia were associated conditions.

Adolescent↗
PubMedDate not supplied

Refractive surgery, optical aberrations, and visual performance.

Visual optics is taking on new clinical significance. Given that current refractive procedures can and do induce large amounts of higher order ocular aberration that often affects the patient's daily visual function and quality of life, we can no longer relegate the considerations of ocular aberrations to academic discussions. Instead, we need to move toward minimizing (not increasing) the eye's aberrations at the same time we are correcting the eye's spherical and cylindrical refractive error. These are exciting times in refractive surgery, which need to be tempered by the fact that after all the research, clinical, and marketing dust settles, the level to which we improve the quality of the retinal image will be guided by the trade-off between cost and the improvement in the quality of life that refractive surgery offers.

Cornea↗
PubMed2000

The calibration of a 2.5x Galilean focusable telescope as an optometer for refraction.

A 2.5x Selsi achromatic Galilean focusable telescope was calibrated for refraction at 6 m. In its calibration, minus power trial lens was placed at the objective of the telescope to simulate vergence of a target at a finite distance, before the back vertex power (BVP) of the telescope at each setting (telescope length) was measured by a focimeter. By using a graphical presentation of the results, the BVP of the telescope at each setting could be determined at different selected target distances. For a target vergence of -0.167 D or a distance of 6 m, the common testing distance in clinical practice, this calibrated telescope had a BVP or refraction measuring range of -7.27(-)+7.52 D. When this telescope was used to measure simulated manifest refractive errors at 6 m, it yielded a mean error of +0.13 D with a 95% confidence limit of agreement of -0.38(-)+0.64 D. These results indicated that the accuracy and precision of telescopic refraction were comparable to that of retinoscopy. Therefore, the calibrated telescope could be considered as a reliable and inexpensive instrument for determining spherical refractive errors. Telescopic refraction is applicable in refracting economically disadvantaged population in underserved areas where modern equipment and electricity are not available. In addition, it provides an alternative subjective refraction method for low vision population because the magnification of this calibrated telescope has the advantage of allowing low vision patients to be refracted at the common 6 m testing distance in clinical practice.

Adult↗
PubMed1998

Lens induced aniso-accommodation.

Despite the evidence for consensual accommodation in response to consensual accommodative stimuli, only a few studies have investigated the binocular accommodative response to unequal (aniso) accommodative stimuli. Past studies investigating an unequal binocular accommodative response (aniso-accommodation) to aniso-accommodative stimuli have been limited by viewing conditions and measurement technique making the results, which were equivocal, difficult to interpret. This investigation addressed these limitations by the following design parameters: (1) monocular dichoptic blur cuese were provided in the binocular stimulus target to provide subjects feedback on their aniso-accommodative response and to alert the investigator of a monocular blur suppression response; (2) a training period was provided; (3) in the subjective method, each eye's stigma was positioned near the dichoptic letter viewed by the other eye. By this method, a true aniso-accommodative response could be differentiated from successive consensual responses; (4) a large range of aniso-accommodative stimuli was used, 0.50-3.0 D, presented in incremental steps of 0.5 D, allowing measurement of an average 0.75 D aniso-accommodative response for the highest (3.0 D) aniso-accommodative stimulus; (5) aniso-accommodation was measured as a function of viewing distance. For four of seven subjects, the gain of the aniso-accommodative response was significantly greater at near than at far viewing distances; (6) aniso-accommodation was confirmed objectively with measures of the response to steady state and step aniso-accommodative stimuli, using a binocular SRI Dual Purkinje Eye Tracker Optometer System. The aniso-accommodative response to step stimuli showed a very long latency period (about 11 s) and a response time of 4.5 s. A potential benefit of aniso-accommodation would be to overcome small amounts of uncorrected anisometropic refractive error. This would preserve fine stereo acuity which is impaired by unequal intraocular image contrast. Aniso-accommodation also may provide an appropriate efferent feedback signal for each eye's unique refractive error which could be used to guide developmental isometropization (attainment of equal refractive error in the two eyes.).

Accommodation, Ocular↗
PubMed1994

Changes in refractive trends and optical components of Hong Kong Chinese aged over 40 years.

The age trends of refractive errors, astigmatism and optical components were studied in 220 Chinese subjects aged over 40 years. Myopia did not dominate in this age group. With increasing age, the prevalence of hyperopia increases from 2% at age 40-45 years to 66% at age > 65 years. Against-the-rule astigmatism was more prevalent than the other types. Significant correlations were found between age and spherical equivalent power, age and vitreous depth and axial length. Sex differences were found among the optical components but not in the refractive error. Myopia appears to be more prevalent among the younger age groups than the older age groups of the Hong Kong Chinese population, and the importance of genetics in determination of refractive error is called into question by these findings.

Adult↗
PubMed1982

Bilateral phakic retinal detachment.

Ninety-nine (11.6%) of 850 phakic retinal detachment patients had bilateral detachments. The incidence of bilaterality was greater in nontraumatic detachments (13.4%) than traumatic detachments (3.8%). Patients were divided into two refractive classes: (1) myopic, containing refractive errors of -2.50 diopters or more, and (2) nonmyopic, containing all other refractive errors. The rate of bilaterality in nontraumatic detachments varied with refractive class and lattice degeneration: nonmyopic without lattice (8.1%), nonmyopic with lattice (14.2%), myopic without lattice (16.3%), and myopic with lattice (24.6%). Mean age in years at onset of the initial detachment varied with refractive class and lattice degeneration: nonmyopic without lattice (59.1), nonmyopic with lattice (55.8), myopic without lattice (49.2), and myopic with lattice (28.2). Lattice degeneration reduced the interval between detachments. Annual risks of fellow eye detachments were calculated for four groups: nonmyopic without lattice (0.12%), nonmyopic with lattice (0.95%), myopic without lattice (1.3%), and myopic with lattice (0.98%).

Eye Injuries↗
PubMed1983

Ocular morbidity in infants of very low birth weight.

In the years 1977-8,258 infants weighing less than 1500 g were born at, or transferred to, the Royal Women's Hospital, Melbourne; 177 (68.5%) survived, and 111 of these attended for an ophthalmic examination. Significant ocular lesions were found in 37 (33%): 21 (19%) children had squint, 19 (17%) had a significant refractive error, 11 (10%) had cicatricial retrolental fibroplasia (RLF), and 3 (2.7%) had very poor vision due to optic atrophy associated with cerebral palsy. No children were blind owing to RLF, indicating that the recent increase in survival rate of infants of very low birth weight has not been accompanied by an increase in the prevalence of severe RLF. In those children with neither cerebral palsy nor RLF the prevalence of squint was 11% and of refractive errors 13%. Myopia was found mainly in children who had shown RLF changes in the neonatal period. It is recommended that infants of very low birth weight continue to be screened in the premature nursery for RLF, and also at the age of 2, for the detection of refractive errors and squint.

Australia↗
PubMedDate not supplied

Three multizone photorefractive keratectomy algorithms for myopia. The Melbourne Excimer Laser Group.

OBJECTIVE: To compare the efficacy and complications of three different excimer laser algorithms for multizone photorefractive and photoastigmatic keratectomy. METHODS: Three different software algorithms were applied to treat myopia and myopic astigmatism with the VISX 20/20 excimer laser. Each algorithm had a maximum ablation zone of 6 mm but differed in the number of zones employed, the proportion of the total treatment allocated to each ablation zone, and the treatment of astigmatism. The Melbourne multizone technique equally divided myopia correction into a maximum of three ablation zones. The Pop multizone technique biased myopia treatment into the smaller diameter zones to a maximum of six ablation zones, with one central island pretreatment. The Alpins multizone technique equally divided myopia treatment through all zones up to a maximum of six, with one central island pretreatment. RESULTS: A total of 585 patients (780 eyes) were treated and 625 eyes (80%) were followed for more than 6 months. The mean baseline spherical equivalent refractive error was -5.63 D (-1.00 to -19.50 D). Between 71 and 79% of eyes were treated for astigmatism. There was no statistically significant differences in baseline refractive error or other characteristics among the three groups. At 6 months, the Alpins multizone algorithm had more eyes with a refractive error within +/- 1.00 D of emmetropia (p = 0.01) and more within +/- 2.00 D of emmetropia (p < 0.01). This new algorithm produced more eyes with an uncorrected visual acuity of 20/20 or better at 6 months (p < 0.01). When multiple logistic regression was used to correct for any differences in baseline myopia among the three groups, this algorithm also had a higher odds ratio for achieving 20/20 or better uncorrected visual acuity (OR = 1.58). CONCLUSION: At 6 months, all three algorithms were effective in the reduction of myopia. Significantly better visual acuity and refractive results were achieved with the Alpins multizone algorithm that spread the total treatment over a larger number of ablation zones, with an equal number of diopters of treatment in each zone.

Adolescent↗
PubMed1994

Results one year after using the 193-nm excimer laser for photorefractive keratectomy in mild to moderate myopia.

As part of a clinical trial, photorefractive keratectomy using the VISX 2015 193-nm excimer laser was performed on 91 healthy eyes of 91 patients. Preoperative refractive errors (spherical equivalent) ranged from -1.00 to -7.50 diopters (mean, -4.16 +/- 1.41 diopters). No patient had more than 1 diopter of refractive astigmatism. Six months postoperatively, the average residual refractive error was +0.09 +/- 0.63 diopters (range, -2.13 to +1.63 diopters). Correction within 1 diopter of that attempted was attained in 85 eyes (93%). Uncorrected visual acuity of 20/40 or better was attained in 86 eyes (95%) and was 20/25 or better in 67 eyes (74%). At one year, follow-up information was available on 85 eyes of 85 patients. The average residual refractive error was -0.15 +/- 0.65 diopters (range, -2.50 to +1.63 diopters). Correction within 1 diopter of that attempted was attained in 85 eyes (93%). Uncorrected visual acuity was 20/40 or better in 83 eyes (98%) and was 20/25 or better in 68 eyes (80%). One patient lost three lines of best-corrected visual acuity because of corneal haze, dropping from 20/15 to 20/30, whereas all other patients returned to best-corrected visual acuity within one line of their preoperative best-corrected visual acuity. Photorefractive keratectomy with the 193-nm excimer laser appears to be a useful treatment modality for the reduction of mild to moderate myopia.

Adolescent↗
PubMed2005

[Advantages and disadvantages of contact lenses in the correction of ametropia].

PURPOSE: The purpose is to appreciate the benefits and the drawbacks in the correction of the refractive errors with contact lenses comparative to the glasses, to see their indications, general contraindications, their specific features. MATERIAL AND METHOD: This is a retrospective study on a group of 100 patients that were consulted during a period between years 2003 and 2004 in the Optimed Clinic of Ophthalmology. RESULTS: The patient's age varied between seven to sixty years, most of them between twenty and thirty years. Women formed the largest group most of the patients lived in the cities. The refractive errors in which we used contact lenses were: myopia, astigmatism, hyperopia, keratoconus. Soft lenses were used more then hard lenses. Only 25 of our patients developed some complications, especially corneal complications. CONCLUSIONS: 1. The contact lenses represent an optimal solution in the correction of refractive errors, especially in young patients. 2. The quality of vision obtained with contact lenses is superior comparative to glasses. 3. Most of their complications can be treated without marks.

Adolescent↗
PubMed1992

The refractive development of the eye of the American kestrel (Falco sparverius): a new avian model.

Most measures of avian visual performance are carried out on commonly available domestic species such as the chicken, and most of the data on avian induced refractive error deals with chickens. Raptors are predatory birds in which good visual resolving ability is particularly important. Behavioral studies indicate that the eyes of raptors have two to three times the resolving ability of the human eye. The domestic chicken is precocial at hatching whereas most raptors are semi-altricial. This study was an effort to determine if the effect of early visual deprivation on the refractive development of the chicken eye can be reproduced in the American kestrel, a species which is not domesticated and in which the need for acute vision is particularly important. Visual deprivation was achieved by unilaterally applying translucent plastic goggles over the eyes of kestrels two days after hatching. Refractive error was measured using a retinoscope and trial lenses. Ocular growth was monitored by A-scan ultrasonography, and frozen ocular sections of sacrificed birds. The effect of the experimental manipulation on the contralateral control eye and body weight was evaluated each day over a 42-day period. The goggles did not significantly affect the normal changes in body weight or the normal pattern of ocular growth and refractive development in the untreated eyes. An analysis of the refractive state changes as a result of form deprivation was made each week for 6 weeks after hatching on both the treated and untreated eyes in a separate group of experimental birds. Visual form deprivation caused a significant myopic shift in refractive error and a significant increase in the vitreous chamber depth in the treated eyes at 3 and 6 weeks of age. However, the amount of myopia produced is much less than that induced in chicks, and in certain cases hyperopia is produced. The kestrels recover from myopia and hyperopia within 10 days of goggle removal, after 3 to 4 weeks of deprivation. This study is the first indication that chickens may not be a representative bird model for studying form-deprivation myopia. First, myopia is not always produced in kestrels in response to form deprivation. Second, kestrels are severely myopic at hatching and therefore, the direction of emmetropization is opposite to that found in hatchling chicks.

Animals↗