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PubMed2006

Two-step laser in situ keratomileusis to correct high astigmatism after corneal autograft.

We report a case in which significant anisometropia and astigmatism after an autograft by rotation was treated by a 2-step laser in situ keratomileusis (LASIK) procedure. Six weeks after the lamellar keratotomy, photoablation was performed using the LADARVision 4000 excimer laser. The ablation depth was 87.2 mum on a 6.0 mm optical zone. One day postoperatively, the uncorrected visual acuity (UCVA) was 7/10 and the refractive error was -0.25 -0.25 x 67. Two months later, the UCVA was 5/10 and the best corrected visual acuity, 8/10 Parinaud 2 with a refractive error of +1.75 -1.25 x 16. The case demonstrates the effectiveness of 2-step LASIK for the correction of astigmatism induced by a corneal autograft. The significant reduction in autograft-induced astigmatism, together with stabilization of the higher-order aberrations, resulted in restoration of satisfactory functional vision.

Anisometropia↗
PubMed1983

Ongoing prospective clinical study of radial keratotomy.

The ongoing prospective clinical study of radial keratotomy at the University of Maryland now includes 58 eyes of 33 patients. Fifty-two eyes underwent a single operation, whereas six eyes underwent two operations. Follow-up was a minimum of six months and a mean of 19 months. Preoperative vision was 20/400 or less in 74% of eyes. Postoperative vision was 20/40 or better in 48% of eyes. There was an average myopia decrease of 2.70 diopters and an average corneal flattening of 1.51 diopters. Patients with preoperative refractive errors of 5 diopters or less achieved 20/40 or better vision in 65% of eyes, as compared to only 19% in eyes with preoperative refractive errors greater than 5 diopters. This is highly significant (P less than 0.005). There was no difference in the results achieved by our first 33 eyes when compared to our second 25 eyes. The decrease in myopia did not correlate with corneal curvature, or whether 8 or 16 incisions had been used. No microperforations were seen and only one case of endothelial cell loss was observed. Glare and fluctuating vision was not a significant problem in our series.

Adolescent↗
PubMed1975

Variations in refractive change induced by Cyclogyl upon children with differing degrees of ametropia.

The effect of cycloplegic drugs on refraction is complicated by the presence of many variables. This study is concerned with one of these: the type and degree of refractive error. A manifest and a cycloplegic refraction were performed on 170 eyes. The difference was determined in each case and tabulated according to the type of ametropia. This experiment showed that in every instance the cycloplegic estimate was equal to or greater in hyperopia or less in myopia than when performed without drugs. The greatest difference occurred in hyperopia, decreasing to zero once myopia was reached.

Accommodation, Ocular↗
PubMed1990

Silicone-acrylate contact lenses for myopia control: 3-year results.

One hundred myopic children between the ages of 8 and 13 years were fitted with Paraperm O2plus silicone-acrylate contact lenses. After 3 years of lens wear, the mean increase in myopia for the 56 subjects remaining in the study was 0.48 D (+/- 0.70) D as compared with 1.53 (+/- 0.81) D for a group of spectacle-wearing myopes matched for initial age and initial refractive error. The mean change in corneal refracting power for the contact lens wearers was a decrease (corneal flattening) of 0.37 (+/- 0.32) D. Assuming that little or no corneal change would have occurred in the absence of the contact lenses, we may conclude that corneal flattening (as measured by the keratometer) accounts for less than half of the effect of contact lenses in controlling myopia progression. A possible explanation for this disparity is that although the keratometer provides a valid measurement of corneal refracting power for a "normal" cornea, it fails to provide a valid measurement for a cornea that has been flattened by wearing a contact lens.

Acrylates↗
PubMed2004

Effects of photorefractive keratectomy-induced defocus on emmetropization of infant rhesus monkeys.

PURPOSE: To investigate whether photorefractive keratectomy (PRK) performed in infant primates can modify emmetropization and therefore could be used to study mechanisms of refractive error development. METHODS: Six healthy rhesus monkeys ranging in age from 2 to 3 months were randomly divided into two groups (n = 3 each). Anisometropia was induced in each animal by performing PRK on one eye. Hyperopic anisometropia was induced in group A monkeys by flattening the cornea of the right eye, whereas myopic anisometropia was produced in group B monkeys by steepening the cornea of the right eye. Corneal morphology and topography, refractive status, and axial growth were evaluated over a 5-month observation period. RESULTS: All the PRK-treated corneas were re-epithelialized and transparent within 3 days after surgery. Subsequently, all the surgically treated eyes exhibited interocular alterations in axial growth rate that were appropriate to compensate for the PRK-induced anisometropia. Specifically, vitreous chamber elongation rates were faster in the eyes with induced hyperopias than in their fellow eyes (0.63 +/- 0.05 mm vs. 0.40 +/- 0.09 mm), but slower in the eyes with induced myopia than in their fellow eyes (0.58 +/- 0.13 mm vs. 0.73 +/-0.10 mm). In some animals, the recovery from the induced anisometropia was facilitated by interocular differences in the rate of corneal flattening. However, the rates of corneal flattening in the treated eyes and their fellow eyes were not significantly different. CONCLUSIONS: PRK-induced defocus predictably alters axial growth rate and the normal course of emmetropization in developing eyes. Thus, PRK is a useful alternative to current methods used to impose experimental refractive errors in laboratory animals. These results also indicate that refractive surgery performed in childhood may affect normal growth of the eye, resulting in decreased predictability of future refractive status.

Animals↗
PubMed1990

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. Perk Study Group.

The Prospective Evaluation of Radial Keratotomy Study is a nine-center clinical trial of a surgical technique to reduce simple myopia by making incisions in the cornea. There were 435 patients (one eye per patient is reported) enrolled in the study with a 91% follow-up rate at 4 years after surgery. After surgery, uncorrected visual acuity was 20/40 or better in 76% of eyes. Fifty-five percent of the eyes had a refractive error within +/- 1.00 diopter; 28% were undercorrected, and 17% were overcorrected by more than 1.00 D. The width of the prediction 90% interval for the refractive change was 4.42 D, indicating a lack of predictability. The refractive error was not stable in some eyes; between 6 months and 4 years after surgery, 23% of eyes had a continued effect of the surgery of more than 1.00 D. For 323 patients with both eyes operated on, 64% stated they wore no optical correction. There were few serious complications. Eleven eyes (3%) lost two or three lines of best corrected visual acuity. Two eyes developed delayed bacterial keratitis without significant loss in best corrected visual acuity.

Adult↗
PubMedDate not supplied

[Occurrence of changes in the eye in diabetic retinopathy with significant myopia].

The optic disc and retinal neovascularization are less prominent and less frequent in myopic eyes in patients suffering from diabetes mellitus. The exact mechanisms of this phenomenon are not well known, but there is some evidence that there is a reduced blood flow in myopic eyes which is associated with less damaged microcirculation in eyes of patients with diabetes mellitus. The aim of our study was to evaluate the correlation between myopic refractive error and degree of diabetic retinopathy. We conducted a retrospective study in a group of randomized patients, divided into the following groups according to their refractive error: emmetropia (30 eyes), myopia simplex (30 eyes) and high myopia, over -6.5 dsph (21 eyes). Among patients with high myopia, seven had monocular myopia. All patients suffered from non insulin dependent diabetes mellitus for more than ten years, and their average age was 52.37-3.48 years. We did not observe patients with rubeosis iridis and neovascular glaucoma or patients with myopia less than -2.0 dsph. Our results indicated that there was no significant difference in the appearance of fundus between the studied groups. In all patients the incidence rate of non proliferative and proliferative diabetic retinopathy was the same as well as the absence of retinopathy (Fisher's test). The only exception were the patients with monocular myopia over -13.o dsph who had no signs of diabetic retinopathy in myopic eye, while the other, emmetropic eye, showed various stages of retinopathy, from severe non proliferative to proliferative. Some of the risk factors which influence the incidence rate of ocular complications in diabetic patients are well known, as are duration of diabetes mellitus, blood sugar level, blood pressure, ocular pressure and eye perfusion. On the other hand, it is also known that amblyopia, optic atrophy, low blood pressure in central retinal artery and retinitis pigmentosa are ocular conditions which are not associated with proliferative diabetic retinopathy. It was also noticed that complications of diabetes in high myopic eyes are less prominent than in emmetropic eyes. This finding is in harmony with our results. Sultanov et al. observed diabetic changes in the retina in 40.9% of myopic refraction patients, 65.2% of emmetropia cases and 70.4% of hypermetropia cases. The severity of involvement was less in myopia than in other types of refraction. In medium severe myopia, no proliferative diabetic retinopathy was observed, and in high myopia (10 eyes) no diabetic involvement of the fundus oculi was found. In anisometropia diabetic symptoms on the myopic side were either absent or poorly manifest. The possible cause of such findings could be the changes in retinal perfusion in myopic eyes and eyes in patients with diabetes mellitus. In 1973 a lower blood flow was detected in the retina and the choroid, proportionally to the degree of myopia. In 1982, Perkins indicated that the circulation time and pulsation rate in the central retinal artery in myopic eyes were reduced proportionally to the degree of myopia. In cases with early diabetic retinopathy Coscas detected a lesser blood flow in retinal veins. On the other hand, it has been found that high blood pressure increases the risk of diabetic retinopathy. These data suggest that the reduced blood flow in high myopia is a protective factor regarding the occurrence of complications in diabetes. Anisometropia and amblyopia in cases with monocular myopia, which presents a particular group in our study, could be factors which also prevent the occurrence of proliferative diabetic retinopathy. Instead of conclusion, we would like to point out that pathophysiologic mechanisms of these phenomena are not discussed enough. It is, nevertheless, important to appropriately examine the fundus in patients with high myopia and diabetes mellitus, because if the complications appear, they may be disastrous and must be treated immediately.

Diabetic Retinopathy↗
PubMed1999

Oculomotor functions and late-onset myopia.

In order to elucidate the role of optical defocus in the development of late-onset myopia (LOM), we employed both theoretical and experimental approaches. In the theoretical study, which has been reported previously, we suggested a model in which an accommodative sensory operator was added to simulate the sensory part of the accommodation system. Results derived from the model showed that the sensory part might increase the system's threshold to the accommodative error (or defocus) signal. In this study, we measured the perceptual depth-of-focus and the system's threshold to the defocus signal for three refractive error groups: emmetropic (Emm), stable myopic (S.M.), and progressing myopic (P.M.). Results show that there are no significant differences in the perceptual depth-of-focus among the three groups. However, the defocus threshold values of the P.M. group are significantly higher than the values of the other two groups. This result in combination with our previous findings, leads us to suggest that individuals susceptible of developing myopia from sustained near-work have a specific oculomotor risk profile. Although we are still trying to determine the specific sequence of changes among dark-focus, AC/A ratio, the accommodative system's defocus threshold, and refractive error, we are convinced that the changes of oculomotor parameters underlie the type of myopia associated with near-work.

Accommodation, Ocular↗
PubMed1995

Progression of myopia.

BACKGROUND: Myopia is an important public health problem because it is common and is associated with increased risk for chorioretinal degeneration, retinal detachment, and other vision-threatening abnormalities. In animals, ocular elongation and myopia progression can be lessened with atropine treatment. This study provides information about progression of myopia and atropine therapy for myopia in humans. METHODS: A total of 214 residents of Olmsted County, Minnesota (118 girls and 96 boys; median age, 11 years; range, 6 to 15 years) received atropine for myopia from 1967 through 1974. Control subjects were matched by age, sex, refractive error, and date of baseline examination to 194 of those receiving atropine. Duration of treatment with atropine ranged from 18 weeks to 11.5 years (median 3.5 years). RESULTS: Median follow-up from initial to last refraction in the atropine group (11.7 years) was similar to that in the control group (12.4 years). Photophobia and blurred vision were frequently reported, but no serious adverse effects were associated with atropine therapy. Mean myopia progression during atropine treatment adjusted for age and refractive error (0.05 diopters per year) was significantly less than that among control subjects (0.36 diopters per year) (P < .001). Final refractions standardized to the age of 20 years showed a greater mean level of myopia in the control group (3.78 diopters) than in the atropine group (2.79 diopters) (P < .001). CONCLUSIONS: The data support the view that atropine therapy is associated with decreased progression of myopia and that beneficial effects remain after treatment has been discontinued.

Adolescent↗
PubMed2006

The influence of incision-induced astigmatism and axial lens position on the correction of myopic astigmatism with the Artisan toric phakic intraocular lens.

PURPOSE: To evaluate postoperative astigmatism with regard to incision-induced astigmatism and deviation in axial alignment with the use of preoperative limbal marking with the Javal keratometer (Haag Streit, Bern, Switzerland) in eyes implanted with the Artisan toric phakic intraocular lens (IOL) (Ophtec, Groningen, The Netherlands). DESIGN: Prospective nonrandomized trial. PARTICIPANTS: Fifty-four eyes of 33 patients with myopia (mean, -9.67 diopters [D]) and astigmatism (mean, -3.44 D). INTERVENTION: The enclavation site was marked on the limbus using the Javal keratometer. The Artisan toric phakic IOL was implanted according to the axis marked on the limbus. Follow-up was a minimum of 6 months. MAIN OUTCOME MEASURES: Safety index, efficacy index, predictability, safety, and vector analysis of total refractive correction were determined. The effects of axis misalignment and incision-induced astigmatism on the final refractive error were evaluated. RESULTS: At 6 months after surgery, the safety index was 1.29+/-0.29 and the efficacy index was 1.04+/-0.35. Mean spherical equivalent subjective refraction reduced from -11.39+/-4.86 D before surgery to -0.38+/-0.57 D at 6 months. Sixty-seven percent of eyes were within 0.50 D of attempted refraction and 89% were within 1.00 D. Mean preoperative cylinder was 2.92+/-1.60 D at 91.4 degrees . At 6 months, the mean cylinder was 0.28+/-0.54 D at 174.3 degrees . No eyes lost 2 or more lines of best-corrected visual acuity at 6 months. Eighty-three percent of eyes achieved uncorrected visual acuity of 20/40 and 28% achieved 20/20. Vector analysis of total surgically induced astigmatism revealed a mean cylindrical change of 3.21+/-1.71 D. Average axis misalignment was 0.37+/-5.34 degrees . The mean incision-induced astigmatism was 0.74+/-0.61 D at 0.2 degrees . CONCLUSIONS: Implantation of the myopic toric IOL leads to safe, efficacious, and predictable results. The level of unpredictability caused by minor axis IOL misalignment has minimal effects on the residual refractive error. The procedure of axis alignment with the Javal keratometer seems to be an accurate method of marking the eye for toric IOL implantation. Incision-induced astigmatism can result in an overcorrection of the cylinder. A systematic undercorrection of -0.50 D for attempted cylindrical outcome could result in an achieved correction closer to emmetropia.

Adult↗
PubMed1986

Epikeratophakia with commercially prepared tissue for the correction of aphakia in adults.

The records of all adult patients at Louisiana State University Eye Center, New Orleans, who underwent epikeratophakia for aphakia with commercially prepared tissue since February 1984 were reviewed. The epikeratophakia lenticule was maintained in 37 (92.5%) of 40 patients; complications required the removal of three tissue lenses. The average refractive error three months after surgery was +0.67 +/- 1.97 diopters; 25 (90%) of 28 patients were within 3 D of emmetropia. At six months, the average refractive error was -0.18 +/- 2.27 D. Fourteen (58%) of 24 patients whose visual acuity was 20/40 or better with spectacles before surgery achieved 20/40 spectacle visual acuity three months after surgery, as did ten (59%) of 17 patients at six months and five (83%) of six patients at 12 months. The results in these recent cases are better than in previously reported series and reaffirm the usefulness of epikeratophakia in the treatment of aphakia.

Adult↗
PubMed1992

Shape of the myopic eye as seen with high-resolution magnetic resonance imaging.

We have obtained multislice magnetic resonance (MR) images of the eye and calculated ocular dimensions along the three cardinal axes: antero-posterior (A-P), equatorial, and vertical. We found no difference in the shape of hyperopic (average refractive error: +3.72 D) and emmetropic eyes, both of which had an equatorial diameter longer than the A-P and vertical diameters. Myopic eyes (average refractive error: -6.54 D) were larger than hyperopic eyes, and most had the same spheroelliptical shape as that of the emmetropic and hyperopic eyes. The results suggest that during myopic progression an overall enlargement or a radial volume expansion has occurred.

Adult↗
PubMed1994

Eleven-year experience with radial keratotomy.

1,900 consecutive eyes that underwent radial keratotomy by the senior author were evaluated retrospectively. 3 months after surgery, minimum reduction in mean spherical equivalent of 0.67D was achieved with 1 incision and maximum 7.25D with 24 incisions. Uncorrected visual acuity of 20/40 or better was obtained in 99.4% of eyes with low myopia, 64.2% with moderate myopia and 32.4% with high myopia. For anisometropia, bilateral RK reduced refractive error from -12. 12D to -5. 22D in more myopic eyes and -8. 18D to -3. 4D in less myopic eyes and unilateral surgeries reduced refractive error from -9. 45D to -3. 85D. Anisometropia after surgery became clinically and physically acceptable and aniseikonia was significantly improved. No vision threatening complications occurred. Our results indicate that radial keratotomy is a relatively safe and effective surgical procedure for myopia.

Adolescent↗
PubMed1993

Reliability of the Otago photoscreener. A study of a thousand cases.

The Otago photoscreener is a 35 mm single len reflex camera in which the flash light comes from a narrow ring around the outer margin of its lens. The margin is also the limiting aperture of the optic system and in the centre of the lens is a flickering fixation light. In a colour photograph taken at a distance of 66 cm from the face of the subject who is accurately focusing on and fixing the camera fixation light with both eyes, the fundus reflex in each pupil is very dark red and the corneal light reflexes are symmetrical. If either or both eyes are not appropriately focused or fixing, the fundus reflex is brighter and yellow or white. This article describes a prospective trial of the performance of the Otago photoscreener in a series of 1000 infants with actual or suspected amblyopia, refractive error or strabismus. In this study photoscreening showed a sensitivity of 94% and a specificity of 79%. Photoscreening also identified some cases of esotropia and of refractive error which were missed on clinical examination. In this series photoscreening passed as normal three children with mild to moderately severe amblyopia. This represents les than 1% of the clinically abnormal children.

Amblyopia↗
PubMed1977

Family distribution of concomitant squint in Greece.

From a study of a large number of brothers and sisters suffering from concomitant squint, the following data were obtained: (1) 42-9% of the patients showed congenital strabismus. (2) In 96-5% of the sibs strabismus was of the same type. (3) The presence of a significant refractive error occurred in 82-8% of the patients. (4) In all twins strabismus appeared at the same age in both twins, and the squint and the refractive error were of the same type. (5) The distance of the patients' homes from Athens had no effect on either (a) the time intervening between the onset of squint and the first visit to the eye specialist, or (b) the effectiveness of treatment.

Age Factors↗
PubMed1992

Refraction changes in children developing convergent or divergent strabismus.

Strabismus and amblyopia were studied in a cohort of children born in 1979 or 1980 in the area of Västerås, Sweden. Forty percent of the children had participated in a voluntary eye examination at 1 year of age. All children diagnosed as strabismic and/or amblyopic between 1979 and 1988 at any of the three eye clinics in the area were included in this study. Strabismic cases were mostly detected by the parents while microstrabismus and straight eye amblyopia were found at the general 4 years of age screening at children's health centres. In 57 cases with (n = 31) and without amblyopia (n = 41) it was possible to obtain several refraction values between 1 and 6 years of age. In this study we concentrated on manifest esotropia and exotropia. The aim of the study was to describe changes of refraction before and after onset of strabismus and to establish risk indicators that identified populations at risk of developing strabismus. We found that patients with esotropia show a more pronounced hypermetropia than exotropic cases at the time of detection of strabismus. This difference becomes more definite over time, since hypermetropia increased in the deviating eye in the esotropic cases while refractive errors remained stationary in most of the exotropic eyes. It was also apparent that anisometropia frequently developed after onset of strabismus in esotropic cases in contrast to exotropic cases. An increasing refractive error in the deviating esotropic eye could be combined with an emmetropisation of the fixating eye.

Anisometropia↗
PubMed1976

A theoretical model for the eye of new-born infants.

A Gullstrand model for the eye of new-born infants is proposed, based on intra-ocular distances obtained by ultrasonography and lens radii measured on sections of deep-frozen preparations (v. Pflugk, 1909). Refractive indices of the media are assumed to be equal or nearly so to those of the adult eye, since no experimental data are available. The focal length of the model is 15.74 mm, the power 84.8 dptr, that of the lens alone 43.4 dptr, and the refractive error +2.8 dptr. A simplified model where the inner surface of the cornea is omitted, has a focal length of 15.63 mm, a power of 85.3 dptr and a refractive error of +2.4 dptr. When the data of v. Pflugk are analyzed statistically it is found that the spread of the lens power is considerably smaller than that which would be expected from the spread of the radii.

Anterior Chamber↗
PubMed2001

Causes of blindness in Northern Tanzania: a hospital and rural health centre based study.

OBJECTIVE: To identify the main causes of blindness in Northern Tanzania. METHODS: Ophthalmic patients at the Kilimanjaro Christian Medical Centre and on outreach clinics in the Kilimanjaro region of Northern Tanzania were examined. The cause of blindness was documented for any eye seeing less than 3/60 Snellen. If more than one factor contributed to the visual loss, the single factor deemed to be the most visually disabling was documented. RESULTS: 1045 blind eyes of 781 patients were examined. 264 patients were bilaterally blind. The main cause of bilateral blindness was cataract [39%]. The other chief causes of blindness were glaucoma, trauma and corneal scarring. The most important cause of corneal scarring, approximately half the cases, was microbial keratitis. Refractive error alone was responsible for 4.2% of bilateral blindness, of which 2.7% was uncorrected post-cataract surgery aphakia. CONCLUSIONS: Treatable causes of blindness, including cataract and refractive error account for over a third of all blindness in Northern Tanzania. Trauma, glaucoma and microbial keratitis are other important causes of blindness in the region.

Adolescent↗