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PubMed2005

[Recent findings on scleral extracellular matrix and matrix metalloproteinases in the development of myopia].

Myopia is the most common eye disorder worldwide. So far there is no effective treatment for the disease. Recent findings indicated that the remodeling of scleral extracellular matrix (ECM) plays an important role in the development of myopia. The dynamic changes of matrix metalloproteinases in myopia (MMPs) activity, one of the most important enzymes that regulates the ECM, has a significant correlation with myopia. This review gives the latest findings about ECM and MMPs in the development of myopia.

Animals↗
PubMed2005

[Changes of eye refraction, corneal power and lens power during growth in emmetropia, myopia and hyperopia].

PURPOSE: The aim of this study was to evaluate changes of eye refraction, corneal power and lens power during growth in emmetropia, myopia and hyperopia. MATERIAL AND METHODS: We examined 183 children (363 eyes) aged 4 to 19 with emmetropia, myopia and hyperopia. All measurements were performed after cycloplegia with 1% tropicamidum. Total refraction and corneal power was examined with autokeratorefractometer. Then we used ultrasound biometer Ocuscan (Alcon, USA), to measure axial length of the eye. Lens power was calculated with use of SRK II formula. RESULTS AND CONCLUSIONS: Mean refractive error in whole group in the age of 4 was +2,86D and was gradually decreasing to reach OD in the age of 14. Between 4th and 14th years old, myopia increases slowly and then acceleration of this process was observed. In hyperopic eyes between 4th and 16th years old, refractive error decreases gradually and then stabilization was noted. Mean corneal power between 4th and 19th years old, decreased in emmetropia and myopia by 1.24D and 2.19D respectively, and increased by 0.38D in children with hyperopia. This changes took place before 10th years old. Mean lens power between 4th and 19th years old, decreased in emmetropia by 2.01 D, in myopia by 1.43D and in hyperopia by 1.78D. This changes took place before 12th years old.

Adolescent↗
PubMedDate not supplied

[Potentialities of preventing progressive and complicated myopia in the light of present-day knowledge].

The paper generalizes the present-day principles of prevention of progressive and complicated myopia. The risk factors of complications and disability due to congenital and acquired myopia are defined. Methods of spectacle, contact, and surgical correction in congenital myopia are discussed. There is evidence for the importance of studies dealing with the etiological factors and pathogenetic mechanisms in determining the ways of preventing myopia. Recommendations are given for the prevention of disabling forms of myopia.

Disease Progression↗
PubMed1991

The amelioration of myopia using biofeedback of accommodation: a review.

The purpose of this review is to give an account of the issues raised by reports that myopia can be treated by operant conditioning or biological feedback. Devices are available that provide auditory feedback of accommodative state such that variation in tone frequency provides a means by which the patient can monitor his or her ability to induce changes in accommodation response, the task thus being to change the pitch of the tone in a direction corresponding to a more distant far point. The aim of a training programme is to reinforce and establish control over the accommodative response by a process akin to operant conditioning and subsequently to transfer the skill to normal visual environments such that a manifest reduction in myopia becomes apparent. Although there are reports that the technique can induce a reduction in myopia by up to 3 D the findings are of limited value owing to the lack of objective data, for example pre- and post-training cycloplegic refraction. The pre- and post-training measures of subjective letter acuity used by many studies are, with repeated trials, particularly vulnerable to individual differences in the ability to learn how to discriminate and interpret blurred images. The review concludes that more comprehensive clinical trials are needed before accommodation biofeedback can qualify as an established method of clinical treatment of myopia. The trials should be designed to encompass the following issues: the characteristics of a feasible physiological model linking accommodation and myopia development; the rationale with regard to patient selection; the technical performance of the optometer employed; the characteristics of the control group used; the criteria for assessment of myopic change; the transfer of training to performance in normal visual environments; the economic viability of the programme of training and equipment; and the skill, training and knowledge of the clinician implementing the training programme.

Accommodation, Ocular↗
PubMedDate not supplied

[Statistical evaluation of the role of elevated intraocular pressure and weakened accommodation in progressive acquired myopia].

Ophthalmic tone was examined by Goldman's tonometry in 186 subjects (372 eyes) aged 13-35 with myopic and emmetropic refraction, as was the status of relative accommodation reserve. The findings evidence that in progressive myopia the mean level of intraocular pressure is by 3.0 mm Hg higher than ophthalmic tone in the eyes with emmetropic and stationary myopia; the relative accommodation reserve index was found decreased in 80-87 percent of patients with slowly and gradually progressing myopia, whereas in those with emmetropic and stationary myopia it was normal. This lead the authors to a conclusion that relatively elevated intraocular pressure (greater than or equal to 16 mm Hg, measured according to Goldman) and poor accommodation are factors indicating the risk of myopia progress and essentially influencing the refraction enhancement at this age.

Accommodation, Ocular↗
PubMed1988

Selected review on genetic factors in myopia.

This article reviews representative literature concerning pedigrees for myopia, heritability studies on refractive error and the ocular components, and other work relating to genetic factors in myopia development. Low myopia most likely reflects the influences of multiple genes. Some types of high myopia may have monogenic inheritance. Refractive error and the ocular refractive components have heritabilities intermediate between zero and one, as complied from several studies, indicating familial resemblance, but also non-genetic variation. It is likely that both heredity and environment have roles in determining refractive status. An understanding of their respective roles awaits the elucidation of the cellular and anatomical mechanisms of myopia development.

Humans↗
PubMed1985

Further observations on use of atropine in the treatment of myopia.

In order to further our observations on the effects of atropine eyedrops for the management of myopia, we conducted a retrospective study of seventy-nine (79) patients, followed over a ten-year period (1971 to 1980). The atropine sulfate drops were used daily in most cases, tapering the frequency in the later teenage years. In general, those children who showed a good initial response during their first year of treatment, continued to use them for several years. Bifocal or reading glasses were used and family acceptance was good. Those children who showed less favorable results in the first year or who had unconcerned parents, stopped the drops within a year or two and went back to glasses or later, contact lenses. The data support the fact that children with low refractive errors may well have "functional myopia," as opposed to the "axial myopia," that characterizes the higher levels of myopia. These low degree myopes are the best candidates for using atropine to reduce or diminish myopia changes.

Adolescent↗
PubMed1985

High prevalence of myopia among young adult Yupik Eskimos.

Myopia is common in Western populations but is considered rare in nonindustrialized population groups. However, studies in undeveloped areas of the Arctic and sub-Arctic have demonstrated increased rates of myopia among young Inuit adults indigenous to the region. We examined the refractive status of Yupik Eskimos, a group that had not previously been evaluated. Our subjects were young adults born between November 1960 and December 1962 to persons living in 10 villages in southwestern Alaska. The refractive status was obtained for 92% of these persons. The prevalence of myopia (refractive error -0.50 D or greater) was 68%, a rate among the highest reported for a general population anywhere in the world. The young women were significantly more myopic than the young men (mean refractive errors -1.91 and -1.36 D respectively). Astigmatism and myopia were positively correlated (r = 0.20, p less than 0.01). The etiology of myopia in this population is under study.

Alaska↗
PubMed1980

Mechanical considerations in myopia: relative effects of accommodation, convergence, intraocular pressure, and the extraocular muscles.

Axial myopia is a common ocular problem characterized by the fact that the posterior sclera has apparently stretched out of shape over a period of several years. The debate persists as to whether myopia is an inherited or acquired disorder. During the last few years, several new laboratory techniques have surfaced which can create large amounts of myopia in normal experimental animals. In an attempt to find a rational mechanical explanation common to both human and laboratory myopia, this report examines the stresses experienced by the posterior sclera as a result of accommodation, convergence, vitreous pressure, and the extraocular muscles. The conclusion is that convergence and, more generally, the tension in the extraocular muscles are mechanically more important than accommodation because of the sizable increase in vitreous pressure. The oblique muscles, because of their attachment sites at the back of the globe near the optic nerve entrance port, have the capability of producing local stress concentrations which may be very important in understanding pathological myopia. Suggestions are offered for future experiments in terms of muscle surgery, the use of prisms, diagnostic techniques, and animal models.

Accommodation, Ocular↗
PubMed1995

Correction of night myopia and glare for night driving.

OBJECTIVE: To assess the effectiveness of treating night myopia. SETTING: Ophthalmic practice in Toronto. PATIENTS: Sixty-one patients aged 18 to 60 years with night myopia and no ocular disease followed for 1 to 14 months (phase 2). Phase 1 (32 patients) was abandoned because of problems with the tint chosen. INTERVENTIONS: Assessment of night myopia with a laser speckle generator, prescription of minus lenses with or without a tint. MAIN OUTCOME MEASURES: Magnitude of night myopia, subjective change in symptoms of night myopia. RESULTS: Nineteen patients (31%) could not benefit from minus or tinted lenses, and eight were lost to follow-up. Of the remaining 34 patients 22 (65%) reported marked improvement in night driving, 9 (26%) had moderate improvement and 3 (9%) had minimal improvement. CONCLUSIONS: Many patients with night driving difficulties can be helped with an increased myopic correction worn at night.

Adolescent↗
PubMedDate not supplied

[Myopia as a complication of retinopathy of prematurity].

Studies were carried out on a total of 103 children, aged 3-15 years, with birth weight 580-2450 g (mean 1710 g), with myopia of various degree. Relationships between axial length of the eye, birth weight, gestational age, duration of oxygen exposure and the degree of myopia were evaluated. Analyses of vascular and retinal changes in the fundus of the eye typical of regressed retinopathy of prematurity were performed. The values of myopia ranged from 1.5 D to 22.0 D (mean (9.78 D) and axial length from 20.36 to 30.9 mm (mean 25.08). The studies revealed that myopia in retinopathy of prematurity is not associated with the axial elongation of the eyeball. No relationship between the degree of myopia and other examined parameters was found.

Adolescent↗
PubMed1993

Education and myopia in 110,236 young Singaporean males.

Computerised data of 110,236 Singaporean males aged 15 to 25 (mean 17.75) years who underwent compulsory medical examination from April 1987 to January 1992 were used to estimate the prevalence and severity of myopia among young Chinese, Malay, Indian and Eurasian Singaporean males with different educational levels. The prevalence and severity of myopia amongst the groups with different educational levels were compared. These groups were fairly well-matched for important known confounding factors such as age, sex, race and degree of urbanisation of place of residence. Our data showed a positive association between educational attainment and both the prevalence and severity of myopia. Both the prevalence of myopia and the proportion of myopes with severe myopia were in general higher among those with more years of formal education.

Adolescent↗
PubMed1993

The development of myopia up to the age of twenty and a comparison of refraction in parents and children.

As a part of a longitudinal birth cohort study, refraction was measured at the age of 20 years in 236 persons known to have had myopia at the age of 14 years and 266 controls (2982 refractions). The earlier the myopia had started, the more myopic the eyes were at the age of 20 years. The greatest mean refraction values, -4.94 D for males and -6.62 D for females were found when the change to myopia had started before the age of 10. The mean progression of myopia (the mean progression curves were achieved by calculating the mean refraction values at different ages) seems to continue at least to the age of 20. A female child with a myopic mother is more likely to develop myopia than a female child with a non-myopic mother and the same relation holds good between a male child and his father. The myopic refractive error seems to be greater in the children than in their parents.

Adolescent↗
PubMedDate not supplied

Circumferential block resection to reduce myopia.

BACKGROUND: The surgical treatment of excessive myopia following penetrating keratoplasty has been largely ignored. Oversized corneal grafts can induce myopia and the Troutman wedge (block) resection has been used to correct astigmatism by removing tissue in a single corneal semimeridian. This study explores the use of block resections in opposing semimeridians to reduce myopia caused by a steep cornea. METHODS: Six eyes received three different operations. One eye received 60-degree block resections in semimeridians located 90 degrees (procedure 1), two eyes received 0.5-millimeter semicircumferential (180 degrees) block resections (procedure 2), and three eyes underwent 0.5-millimeter 360-degree circumferential block resections (procedure 3). All patients were followed for at least 1 year. RESULTS: Procedure 1 (two 60-degree block resections) developed approximately 2.75 D of myopic correction at 1 year. The average reduction of spherical equivalent was 4.50 D for procedure 2 (one 180-degree block resection) and 10.50 D for procedure 3 (one 360-degree block resection) at 1 year. Although all eyes regained best spectacle-corrected visual acuity, the postoperative course was prolonged by irregular astigmatism. CONCLUSIONS: Circumferential and semicircumferential block resections can reduce myopia after penetrating keratoplasty and in naturally-occurring myopia, but the postoperative course can be prolonged, especially because of irregular astigmatism. Early removal of sutures results in regression of myopic correction.

Adult↗
PubMed1993

Atropine reduces experimental myopia and eye enlargement via a nonaccommodative mechanism.

PURPOSE: To determine whether the muscarinic antagonist atropine effectively reduces or prevents experimentally induced myopia via a nonaccommodative mechanism. METHODS: Chicks were monocularly deprived (MD) of pattern vision by placement of a translucent occluder over the left eye. In two of the three MD groups, chicks received a series of intravitreal injections of atropine (n = 8) or saline vehicle (n = 8) with MD. Control groups (n = 8) of chicks were employed to assess the effects of MD, intravitreal injections, and drug effects. RESULTS: In sham-injected or saline-injected MD chicks, 8 days of MD produced -18.5 D and -20.9 D of experimental myopia, respectively. In atropine-injected MD chicks, 8 days of MD produced only -2.8 D of experimental myopia. This significant reduction in experimentally induced myopia in atropine-injected MD chicks was associated with a marked reduction in the relative axial elongation of the deprived eye (0.21 mm) when compared to saline-injected or sham-injected MD chicks (1.04 mm and 1.00 mm). This reduction in axial length in atropine-injected MD chicks was predominantly the result of a reduction in vitreous chamber elongation, although a reduction in anterior segment depth also was observed. Mean equatorial diameter was significantly reduced in atropine-injected MD chicks compared to saline-injected and sham-injected MD chicks, although to a lesser extent. Control experiments demonstrated that intravitreally injected atropine did not reduce carbachol-induced accommodation or light-induced pupil constriction in the skeletal intraocular muscles of the chick eye. CONCLUSIONS: These findings demonstrate that chronic administration of the muscarinic antagonist atropine prevents experimentally induced myopia in chick via a nonaccommodative mechanism.

Accommodation, Ocular↗
PubMedDate not supplied

Four-incision radial keratotomy for high myopia after penetrating keratoplasty.

BACKGROUND: High amounts of myopia can frequently produce anisometropia and limit visual rehabilitation by conventional means in eyes with clear corneal grafts. This condition is frequently coupled with large amounts of astigmatism. Four-incision radial keratotomy provides a way to reduce myopia in normal individuals. In our present study, we used the technique of four- incision radial keratotomy to reduce myopia in a group of keratoplasty patients who failed conventional visual rehabilitation. Arcuate or transverse keratotomy was used in conjunction with radial keratotomy in eyes with high amounts of astigmatism. METHODS: This study retrospectively examined a group of 11 eyes with penetrating keratoplasty which underwent four-incision radial keratotomy for the treatment of visually disabling myopia. The radial incisions were placed in the graft, inside the graft-host interface. Seven eyes underwent concomitant arcuate relaxing incisions at the graft-host interface for treatment of associated astigmatism. One additional eye had paired straight transverse incisions for the treatment of astigmatism. The mean postoperative follow up was 16 months (range, 3 months to 5 years). RESULTS: There was a mean reduction of the spherical equivalent refraction of 3.48 diopters (D) (range, 0.25 to 7.75 D). The eight eyes undergoing astigmatic surgery showed a mean reduction in keratometric astigmatism of 2.25 D (range, -6.75 to +6.50 D) and refractive astigmatism of 4.63 D (range, -1.50 to -9.50 D). Nine of the 11 eyes had stable or improved best spectacle corrected visual acuity. Two eyes had reduction of best spectacle corrected visual acuity--one due to development of irregular astigmatism and one due to worsening of preexisting macular edema. CONCLUSIONS: Four-incision radial keratotomy can reduce myopia after penetrating keratoplasty when the patient is unable to tolerate spectacle or contact lens correction. It can be combined with relaxing incisions or transverse keratotomy to reduce astigmatism. There is a high amount of variability, and predictability is currently limited by the complex topographical changes occurring in corneal transplants. Complex corneal biomechanical changes may predispose these eyes to the development of irregular astigmatism.

Adult↗
PubMed1996

Form-deprivation myopia induces activation of scleral matrix metalloproteinase-2 in tree shrew.

PURPOSE: To investigate whether structural changes to the sclera during form-deprivation myopia are caused by active tissue remodeling, the gelatinase activity of tree shrew scleras was studied in normal animals, form-vision deprived animals, and animals recovering from myopia. METHODS: Infant tree shrews were monocularly deprived (MD) of form vision with translucent occluders for 5 days. Recovery animals were allowed 3 days of binocularly unoccluded vision after the period of form deprivation. Eyes were removed and dissected to provide scleral samples corresponding to equatorial and posterior regions. Gelatinase activity was assessed by quantitative sodium dodecyl sulfate-polyacrylamide gel electrophoresis or SDS-PAGE, gelatin, zymography of scleral matrix metalloproteinase (MMP) extracts. RESULTS: The major gelatinolytic species present in tree shrew sclera was found to be MMP-2 (gelatinase A). In normal (nondeprived) animals, most of the MMP-2 was found to be in the latent form (the ratio of active-to-latent MMP-2 was 0.23 +/- 0.05 and 0.34 +/- 0.06 in equatorial and posterior samples, respectively; n = 10 eyes from five animals). After 5 days of MD, there was a threefold increase in the amount of active scleral MMP-2 in myopic eyes compared to contralateral control eyes, whereas latent MMP-2 activity levels were not altered significantly. This increase in active MMP-2 was seen in both the equatorial and posterior sclera of myopic eyes (active-to-latent MMP-2 ratios were 0.53 +/- 0.10 and 0.81 +/- 0.09 in equatorial and posterior regions, respectively; n = 6 animals). Contralateral control eyes had levels of both active and latent MMP-2 not significantly different from normal eyes. After only 3 days of unoccluded vision, previously deprived eyes that were now recovering from myopia had a fivefold lower level of active MMP-2 than that seen in deprived eyes after 5 days of MD. In fact, active (and latent) MMP-2 levels were reduced in recovering eyes even below the levels found in their contralateral control eyes. Active-to-latent ratios for recovering eyes were 0.11 +/- 0.03 and 0.15 +/- 0.03 in equatorial and posterior sclera, respectively (n = 5 animals). CONCLUSIONS: These results demonstrate that form-deprivation myopia and recovery from myopia alter scleral catabolism and provide further support for the theory that changes in eye size during mammalian refractive development are the result of active tissue remodeling rather than passive scleral stretching alone.

Animals↗
PubMed1996

Myopia in neurofibromatosis type 1.

We studied the prevalence of myopia in 17-year-old Israeli military recruits with neurofibromatosis type 1 (NF1). Twenty-four percent of the youngsters with neurofibromatosis had myopia, compared to 19% of the controls; this difference was statistically significant (P < 0.03). The recruits with NF1 had a slightly lower IQ, fewer years of education, and lower height and weight than the controls. Thus, these factors, which have been reported to be associated with myopia, did not significantly influence the high prevalence of myopia in the neurofibromatosis subjects. A high prevalence of myopia seems to be an additional feature of NF1.

Adolescent↗