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PubMed1991

A comparison of clinical acuity and contrast sensitivity charts: effect of uncorrected myopia.

We have examined the effect of corrected and uncorrected myopia on visual acuity and contrast sensitivity using a standard acuity chart and two commercially available printed contrast sensitivity charts (Vistech and Pelli-Robson). We tested 140 eyes of 70 young adults. Most subjects were myopic and were tested with and without their optimum spectacle or contact lens correction. We found no effect of myopia, if well corrected, on acuity or contrast sensitivity. All three test scores were sensitive to uncorrected myopia. The Pelli-Robson contrast sensitivity chart, which was designed to be insensitive to defocus, required more than three diopters of refractive error to elicit a two line change in performance, and it was generally very insensitive to uncorrected myopia. Although the Vistech chart was sensitive to uncorrected myopia, the large step sizes used in the chart, and the higher inter- and intra-subject variability in scores reduces its potential value for refraction. The Snellen letter chart gave the most sensitive and reliable changes in performance with uncorrected myopia.

Adult↗
PubMed1991

[Photoablative, refractive keratectomy in treatment of myopia. A case study of 134 myopic eyes with 6-months follow-up].

A total of 106 myopic eyes and 134 eyes with sight were operated on with photorefractive keratectomy. To perform these operations the two surgeons used an excimer laser made by Aesculap-Meditec, emitting a wavelength of 193 nm. Patients were assigned to one of four groups according to refraction. The majority of patients had moderately high to high myopia, i.e., over 6 D. All patients could no longer wear spectacles or had developed contact lens intolerance. The follow-up period extended over 6 months. Depending upon the amount of correction desired in myopia, i.e., between -3D and -15 D, we ablated between 30 and 130 microns of the central corneal stroma after abrading the epithelium. The optical zone had a diameter of 5 mm. Three months after the operation a reduction of myopia by 10.6 D had been achieved in the group with moderately high myopia (10-20 D). In the group of high myopia (over 20 D), the mean correction was 13.4 D. In the group with refraction between 0 and 6 D, 88% of the eyes treated had attained a correction between -1 and +1 D 3 months postoperatively. The results in the group with myopia between 6 to 10 D were similar attaining a refraction of -1 and +1 D. Regression of 2 to 5 D occurred in all patients during the follow-up period of 6 months, depending on the degree of correction. We noted a slight subepithelial reticular haze in all eyes. In 98% of the cases the haze was clinically irrelevant.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

[Correction of severe myopia by refractive lamellar keratoplasty without freezing].

The analysis of 56 successive procedures for correction of severe myopia enables us to determine the indications of the two surgical techniques we use: Myopic keratomileusis or Myopic Epikeratophakia. The results are very different. They are reliable and steady throughout one year for certain myopias, but more uncertain for more severe ones. This led us to distinguish two subgroups: the first includes the initial myopia equal to or less than -15 dioptres, the second includes the more severe myopia. Epikeratophakia, always implemented using fresh lenticules corrects more severe myopias than keratomileusis (from -15 to -30 dioptres). So, the indication for epikeratophakia depends on the initial ametropia, as well as on refractive parameters such as keratometry. With the same myopia, an anterior curvature radius over 8.2 mm will render a myopic keratomileusis less efficient then a myopic epikeratophakia. The results with one year follow up are more predictable and stable for the first subgroup. The second group and those cases corrected by epikeratophakia had less predictable results.

Corneal Transplantation↗
PubMed1990

Experimental myopia in tree shrews.

When deprived of form vision during postnatal development, tree shrews reliably develop an axial myopia characterized by elongation of the vitreous chamber, zonular dysplasia and a slight reduction in lens weight and thickness. Corneal flattening has been observed in animals visually deprived by eyelid suture but is absent in animals visually deprived with an opaque goggle. The sensitive period for myopia development starts about 15 days after the eyes open and sensitivity remains high for about 3-4 weeks thereafter. Recovery from experimental myopia can occur in tree shrews that are visually deprived using goggles for a short period. Blockade of action potentials from ganglion cells in deprived eyes by intravitreal injections of tetrodotoxin (TTX) does not prevent the development of myopia, suggesting that local retinoscleral mechanisms can contribute to experimental myopia in this species. Open eyes receiving intravitreal injections of either saline or TTX have shorter vitreous chambers than control eyes, suggesting that puncturing the globe reduces forces within the eye that contribute to its expansion. Animals treated intraperitoneally with lathyritic agents to block collagen cross-linking for three weeks during a 75-day period of monocular visual deprivation develop a very large myopia in the visually deprived eye that is accompanied by a large vitreous chamber elongation and marked thinning of the posterior sclera. The results from studies in tree shrews are consistent with the suggestion that an internally driven expansion acts in concert with ocular growth to increase the axial length of the eye, helping to move the eye from hyperopia toward emmetropia. The resistance of the sclera and/or choroid to this expansion may be affected by activity within the retina. Increased retinal activity associated with achieving a clear image on the retina may result in increased resistance to expansion, helping to hold the retina at the focal plane. Recovery may occur by a slowing of axial expansion while the optical surfaces proceed toward adult values.

Aminopropionitrile↗
PubMed1989

[The biomechanical properties of the crystalline lens capsule in emmetropia and myopia].

Morphometric and electronmicroscopic studies of the capsule of a clear lens depending on the degree of myopia and age as compared with the capsule of a clear lens in emmetropia and myopia have shown that with age the anterior capsule of a clear lens becomes thicker, while the posterior capsule becomes thinner and increases in length. This is connected with the weakening of accommodation in the presence of different curvature of the anterior and posterior surfaces of the lens on the background of the lowering of the metabolic level in elderly persons. In myopia, with the development of age changes the thickness of the lens capsule remains almost unchanged. The degree of myopia doesn't influence the thickness and the length of the anterior capsule of the lens, while with the rise of myopia the thickness of the posterior capsules increases. No dystrophic changes in the structure of such a capsule in high myopia were revealed. Hypertrophy of the posterior capsule speaks about the increase of its mechanic strength in a clear lens and is connected with the weakness of accommodation. Such a capsule can serve as a support for IOL implants in patients with myopic refraction.

Adult↗
PubMed1989

[Scleroplasty as a prophylaxis against blindness and asthenopia in children with progressive myopia].

Remote results from 1.5 to 5 years, after sclera-enhancing operations on occasion of myopia in 51 children, of them 17 with congenital, 13--early acquired and 21--school myopia, have shown stabilization of school myopia in 88.9%, congenital--in 87% and early acquired--in 75% of cases; a rise of visual acuity in school and early acquired myopia is observed in a greater number of cases, than in congenital myopia. Scleroplasty is one of main methods to prevent blindness and poor vision in children with myopia.

Asthenopia↗
PubMedDate not supplied

[Mathematical analysis of the causes of unsatisfactory results of scleroplasty in progressive myopia].

Mathematical statistics-based analysis of the results of 256 surgeries, carried out in 219 patients with high progressive myopia, has revealed a number of factors significant for effective outcomes and failures of the operations. Among prognostically favorable factors are the school and congenital forms of myopia, young or adult age of the patients, a moderate progress of myopia (up to 1 diopter yearly), a noninherited pattern of myopia or a dominant type of inheritance, absence of somatic diseases. The factors that predict a possible unfavorable outcome are early acquired myopia, patients' childhood age, high rate of myopia progress, the recessive type of inheritance, concomitant diseases. The contribution of every factor to the result has been determined. The analysis has helped single out the group of patients at risk of an unfavorable result of surgery.

Adolescent↗
PubMed1983

Epidemiologic research on the role of studying and urban environment in the development of myopia during school-age years.

Four hundred seventy-four Greek male subjects received an ophthalmologic examination and completed a questionnaire. The following were found: (1) the years of studying and urban residence are factors that strongly influence the prevalence of myopia; discriminant factor analysis classified correctly 81% of the subjects into the myopic or the nonmyopic group; (2) the incidence of myopia is significantly higher in the studying v the nonstudying groups; (3) the prevalence of myopia is higher in the more educated group; (4) there is no statistical difference between the orientation of myopes and nonmyopes toward studies or other occupations; (5) although the presence of myopia is determined by the years of studying and urban residence, the degree of myopia is not influenced to a statistically significant level by these factors; and (6) the results indicate that the interaction of these two variables is more significant in their contribution to the onset of myopia than the sum of each variable alone.

Adolescent↗
PubMed1995

Parameters of accommodative and vergence systems and the development of late-onset myopia.

PURPOSE: To evaluate whether the characteristics of the oculomotor system are related to the development of late-onset myopia. METHODS: Forty-four college students were followed for 2 to 3 years. When recruited, 33 of the 44 subjects had emmetropia whereas the remainder (N = 11) had late-onset myopia (LOM). For each subject, dark-focus, dark-vergence, response AC/A, and CA/C ratios, and manifest refraction were measured at 6-month intervals. RESULTS: The mean dark-focus and AC/A ratios for the subjects (N = 6) who started with emmetropia and became myopic were higher than for the subjects (N = 25) who remained emmetropic. These higher values presented before the refractions exceeded -0.50 D. Interestingly, 7 of 11 subjects with LOM whose myopia increased displayed higher mean AC/A and dark-vergence values and lower mean dark-focus values than the subjects who remained emmetropic. CONCLUSION: The lower dark-focus values found among subjects with LOM seems to be a consequence of the development of myopia. However, myopia might eventually develop in a person with emmetropia with a relatively high AC/A and/or dark-focus values. Therefore, AC/A and dark-focus values may be predictors of the development of myopia.

Accommodation, Ocular↗
PubMedDate not supplied

[Study of immune reactions to collagen in patients with myopia].

Fifty-five blood sera and twenty-three samples of lacrimal fluid of patients with medium and high myopia were tested for antibodies to the main structural protein of the sclera, collagen, by enzyme immunoassay. Serum autoantibodies to collagen were detected in 50-70% of patients with all forms of myopia (congenital, early acquired, and acquired at school age). Antibodies to collagen were not detected in the lacrimal fluid, which was regarded as an evidence of the predominance of systemic autoimmune reactions. Antibody titers were the highest in the blood sera of patients with uncomplicated and slowly progressing myopia. Rapidly progressing myopia complicated by mixed forms of peripheral vitreo-chorioretinal dystrophies, including ruptures of the retina, was characterized by a deficit of antibodies to collagen in the blood serum. This implies a possible protective role of antibodies to collagen detected in the blood of patients with myopia. These results are regarded as a proof in favor of the participation of autoimmune reactions to collagen in the pathogenesis of medium and high myopia.

Adolescent↗
PubMed1994

Can contact lenses control the progression of myopia?

Myopia is a potentially blinding condition with serious socio-economic ramifications. Many causes have been alluded to and one of the strongest associations is that of formal education and nearwork. Studies done both locally and abroad illustrate this. In addition, Singaporeans were found to have one of the highest incidences of myopia in the world. Many methods, including the use of contact lenses, have been advocated in the control of myopia. Hard contact lenses and more recently, rigid gas permeable lenses, have been studied both to arrest the progression of myopia in the young and reduce existing myopia (by orthokeratology) in the Caucasian population. However, the Asian eye differs from the Caucasian eye. This is evidenced by the increased frequency and severity of myopia, and the difference in the pattern of corneal diseases in our population. As such, there is a need for local studies to be conducted to assess the effectiveness of this method in our population.

Adolescent↗
PubMed1994

The effect of parental history of myopia on children's eye size.

OBJECTIVE: To evaluate whether eye size and shape are different in children based on their parental history of myopia. DESIGN: A community-based cohort study of schoolchildren (aged 6 to 14 years), the Orinda (Calif) Longitudinal Study of Myopia. SETTING: Four campuses of the Orinda Union School District, a predominantly white, high socioeconomic status community. PARTICIPANTS: A cross-sectional volunteer sample of 716 children (662 non-myopic) in the first, third, and sixth grades in 1989, 1990, and 1991. All children in those grades were eligible for inclusion in the study. INTERVENTION(S): None. MAIN OUTCOME MEASURES: Refractive error (measured by autorefraction), corneal curvature (measured by photokeratoscopy), crystalline lens power (measured by video phakometry), and axial ocular dimensions (measured by ultrasonography). RESULTS: With prevalent cases of myopia excluded and grade in school and "near work" controlled for, children with two myopic parents had longer eyes and less hyperopic refractive error (analysis of covariance, P < or = .01) than children with only one myopic parent or no myopic parents. A model incorporating parental history is only improved by the addition of near work for the prediction of refractive error. CONCLUSIONS: Even before the onset of juvenile myopia, children of myopic parents have longer eyes. These results suggest that the premyopic eye in children with a family history of myopia already resembles the elongated eye present in myopia.

Adolescent↗
PubMed1993

Myopia and myopic progression among schoolchildren: a three-year follow-up study.

PURPOSE: To discuss the factors that might explain the rate of myopic progression and the degree of myopia after a 3-year follow-up among schoolchildren with myopia. METHODS: Myopic progression among 238 schoolchildren was followed up in a randomized clinical trial of myopia treatment. The associations between the explanatory factors and myopic progression and the final value of the spherical equivalent after the follow-up were studied by analysis of variance and regression analysis. RESULTS: Myopia progressed faster among girls than boys. According to the regression models for the boys, 25% of the variation of myopic progression and 57% of the final spherical equivalent could be explained by initial spherical equivalent, age at receiving first spectacles, time spent on sports and outdoor activities, and on reading and close work. Among the girls, 30% of myopic progression could be explained by age at receiving first spectacles, time spent on reading and close work, and reading distance. Similarly, 49% of the final spherical equivalent could be explained by age at receiving first spectacles, initial spherical equivalent, time spent on reading and close work, and reading distance. The rest of the variations could not be explained by the variables measured in this study. CONCLUSIONS: The factors with the most significant relationships to myopic progression were sex, age of onset, and degree of myopia at the beginning of the follow-up. Myopic progression and final myopia were related to time spent on reading and close work and to reading distance but not, however, to accommodation stimulus.

Accommodation, Ocular↗
PubMed1995

Pirenzepine prevents form deprivation myopia in a dose dependent manner.

Previous studies have demonstrated that muscarinic antagonists, such as atropine and pirenzepine, block form deprivation myopia in avian and mammalian models. The aim of the present investigation was to establish dose-response curves for intravitreal and subconjunctivally injected pirenzepine and to determine receptor specificity. Chicks were monocularly deprived of form vision for five days and received daily injections of either pirenzepine or saline. Keratometry, retinoscopy and A-scan ultrasonography of axial ocular dimensions were then taken. Intravitreally injected pirenzepine was effective at preventing form deprivation myopia in a dose dependent manner with an ED50 of 175 micrograms. A 500 micrograms dose totally prevented induced myopia (+0.9 D versus -13.7 D) and axial enlargement (-0.14 mm versus +0.32 mm). Daily subconjunctival injection of pirenzepine was significantly less effective in preventing form deprivation myopia. Form deprivation myopia could still be induced in animals which had undergone pirenzepine treatment. Pirenzepine was effective in preventing the axial elongation associated with experimental myopia in a dose dependent manner and via a functional not toxic mechanism.

Animals↗
PubMed1995

[Examination and analysis on keratometry and axis of myopia].

In this study, we applied SYSTAT software package to deal with the data, measured the keratometric values and axes of 276 patients with myopia (523 eyes), analyzed on the data of keratometry and astigmatism, correlations between the myopic degree and keratometric value and between the former and length of axis, and pathogenesis of myopia. The results revealed that the vertical corneal refractive power was stronger than the horizontal value, the vertical corneal refractive power in high and superhigh myopia was greater than that in mild and medium myopia, the axial lengths are significantly different among mild, medium, high and superhigh myopia (P < 0.01), and the myopic degree is correlated with the keratometric value and axial length. We can conclude that keratometry and axis are two main factors for the formation of myopia.

Adolescent↗
PubMed1996

IOP in myopic children: the relationship between increases in IOP and the development of myopia.

Intraocular pressure (IOP) was measured at yearly intervals, from age 7 to 9 years, in 106 Chinese children. The sample had been selected from newborn children for participation in a growth and nutrition study, and all children remaining in this study took part in the myopia study. As part of an ongoing prospective study to examine factors which may be associated with the development of myopia, IOP was compared according to whether the subjects had become myopic or remained non-myopic during the time-frame of the study. During the course of the study 13 children became myopic. There was no difference in the IOP of the incident compared with control groups at age 7 years. The IOP of the incident group was higher following onset of myopia than it was prior to onset whereas there was no difference in the IOP of the control groups over the same period. A high IOP therefore follows the onset of myopia and cannot cause myopia. It is still unknown whether or how myopia causes a high IOP.

Analysis of Variance↗
PubMed1997

Laser In Situ keratomileusis (LASIK) for the treatment of low moderate, and high myopia.

PURPOSE: To evaluate the efficacy, safety and predictability of LASIK in the treatment of low, moderate and high myopia. METHODS: A perspective study of LASIK for low myopia of -0.75 to -6.00 with less than +1 D of astigmatism and for moderate and high myopia of -6.12 to -20 D with astigmatism up to +4.50 D was performed at our institution from March through November, 1996. The Chiron automated corneal shaper was used for the initial flap, and either the Summit or VISX laser was used for the refractive ablation. Preoperative refraction, uncorrected and corrected visual acuity were compared to postoperative refraction, uncorrected and corrected visual acuity. One day and 1 month results were available on all patients. RESULTS: In the low myopia group 101 eyes underwent LASIK with a mean preoperative spherical equivalent of -4.16 +/- 1.41 D (-0.75 D to -6.00 D). Mean preoperative astigmatism was +0.4 +/- 1.29 D (0 to 0.75 D). At 1 day, 48% were 20/25 or better and 80% were 20/40 or better. The day 1 mean spherical equivalent was +0.4 +/- 0.75 D with 86% between +/- 1.00 D of emmetropia. At 1 month, 50% were 20/25 or better and 90% were 20/40 or better. The 1 month mean spherical equivalent was -0.26 +/- 0.65 D with 89% between +/- 1.00 D of emmetropia. In the high myopia group 198 eyes underwent LASIK with a preoperative mean spherical equivalent of -8.34 +/- 2.15 D)-6 to -20D) and a mean preoperative astigmatism of +1.18 +/- 0.88 D (0 to +4.5 D). At 1 day postoperatively, 17% were 20/25 or better, and 61% were 20/40 or better. The mean day one spherical equivalent was -0.26 +/- 1.56 D with 58% between +/- 1.00 D of emmetropia. At 1 month, 35% were 20/25 or better and 71% were 20/40 or better. The 1 month mean spherical equivalent was -0.28 +/- 1.18 with 63% within +/- 1.00 D of emmetropia. CONCLUSION: Early results of using LASIK to treat low, moderate and high degrees of myopia with and without astigmatism appear promising, although longer follow-up and nomogram refinement are needed.

Adult↗
PubMed1995

Excimer laser photorefractive keratectomy (PRK) for myopia--present status: aerospace considerations.

UNLABELLED: Excimer laser photorefractive keratectomy (PRK) to reduce myopia has been studied the past 3 yrs at multicenters authorized by the FDA. The excimer laser ablates the central cornea to a new calculated power. A review of the cases reported in the literature reveals the following information: Corneal scarring may be reflected in the loss of best-corrected vision. Regression of the refractive effect is a complication. Predictability was the percentage of eyes obtaining 20/40 or better vision; this varied from 62.5-91%. Conversely, 9.0-37.5% were 20/50 or worse. Low to moderate myopes had better visual success. Accuracy was the refractive correction within +/- 1.00 D (spherical equivalent); this varied between 64.7-93%. The higher percentages were with low to moderate degrees of myopia. Loss of best corrected vision was due to scarring and haze, and occurred more frequently with high myopia and deeper ablations. Patient satisfaction after 2 yrs was reported as 82.6-90%; 17.4% were not satisfied. ADVANTAGES: a) PRK effectively and safely corrected myopia and myopic astigmatism; b) there was no diurnal variation of refraction or vision; c) vision remained fairly stable with some regression up to 24 mo and; d) accuracy of correction to +/- 1.00 D was fair. Disadvantages: a) post-operative scarring and haze was present after 6 mo to 2 yrs of follow-up in some cases. Scarring was less with low myopia and worse with high myopia; b) regression of correction and blur; and c) poor night vision, halos, and glare sensitivity occurred after pupil dilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerospace Medicine↗