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At least 19 recordsLinked to original sources

PubMed1995

How applicable are animal myopia models to human juvenile onset myopia?

Investigations into the plasticity of eye growth and refractive error development have significantly expanded our knowledge of animal models of myopia in the last 15 yr. The applicability of this information is as yet undetermined, but hopefully this information will be useful in learning more about human myopia. This paper presents a critical review of the animal myopia literature as those data relate to the human condition. Differences between the chicken, tree shrew, and primate animal models of myopia are outlined, and the various experimental paradigms used to investigate refractive error development and ocular growth in the chicken are compared. Specific arguments against the application of animal models of myopia to the etiology of human juvenile onset myopia include the following: (1) there is no deprivation of form vision in the environment of the school-aged child as severe as that required to induce myopia in animals; (2) the sensitive period for deprivation myopia in animals appears to be too early to account for human juvenile onset myopia; and (3) studies in the chicken using spectacle lenses to create dioptric blur involve a choroidal thickness modulation that has no human analog. Ultimately, the results of investigations into the cellular and biochemical modulation of eye growth in animals may be the most relevant to human myopia.

Animals↗

PubMed2002

Genetic loci for pathological myopia are not associated with juvenile myopia.

The purpose of this study was to evaluate chromosomal regions previously linked to pathological myopia for linkage to juvenile myopia in a sample of myopic children and their families. Of 125 families with a myopic child participating in the Orinda longitudinal study of myopia, 53 submitted 221 buccal swab samples for genetic analysis. Myopia in proband children was defined as -0.75 D or more myopia in both meridians on cycloplegic autorefraction (1% tropicamide). Affected status in parents and siblings was obtained by survey. DNA was extracted from buccal mucosal cells, amplified by polymerase chain reaction (PCR), and then analyzed with seven markers for chromosome 12 and five markers for chromosome 18 in the regions previously associated with pathological myopia. LOD scores were not significant for any marker tested. The largest positive LOD score was 0.15 for GATA30F04. Model-free methods using a SimIBD approach suggested a possible linkage at one marker, GATA6H09 (P = 0.003), but these results were not supported by transmission disequilibrium test (TDT) analysis. The statistical power to detect LOD scores of > or =1.0, assuming homogeneity, was estimated at 93.2%. We found no confirmatory evidence of linkage between juvenile myopia and regions of chromosomes 12 and 18 previously associated with pathological myopia.

Child↗

PubMed1996

Clinical findings before the onset of myopia in youth: 4. Parental history of myopia.

BACKGROUND: We conducted a study to compare variables in children who were initially emmetropic and became myopic to those in children who remained emmetropic. This paper examines parental history of myopia in the two groups of children. METHODS: A cohort of initially emmetropic children was given eye and vision examinations at 6-month intervals for 3 years. Data on parental history of myopia were obtained by questionnaire. RESULTS: A greater proportion of children in the became-myopic group had myopic parents compared to children in the remained-emmetropic group. The sensitivity for onset of myopia was 0.95 and specificity was 0.38 if at least one parent was myopic. A sensitivity of 0.36 and a specificity of 0.87 were found for both parents being myopic. There was a significant association between parental history of myopia and development of myopia in the children in the study (p < 0.01 by chi 2 for categorization of whether neither, one, or both parents were myopic for children in the became-myopic and remained-emmetropic groups). CONCLUSION: Parental history of myopia is a risk factor for the development of myopia.

Child↗

PubMed1998

Baseline characteristics in the Myopia Progression Study, a clinical trial of bifocals to slow myopia progression.

BACKGROUND: Retrospective studies have indicated that myopic children with nearpoint esophoria experienced slower myopia progression if they wore bifocal glasses rather than single-vision glasses. A small, 18-month clinical trial also supported that finding, but the results were not statistically significant. The Myopia Progression Study was funded by the National Eye Institute to test more rigorously the efficacy of bifocals, compared with single-vision glasses, in slowing myopia progression in children with nearpoint esophoria. A secondary objective of the study was to identify other variables that might influence the rate of myopia progression. This report describes the design and methods of the Myopia Progression Study and the baseline characteristics of the subjects. METHODS: A 3-year, randomized clinical trial was initiated. Subjects were children between 6 and 12 years of age who were myopic (at least -0.50 D in each eye) and who demonstrated nearpoint esophoria by the von Graefe technique. RESULTS: Eighty-two children were enrolled. After blocking by gender and clinical site (two sites), subjects were randomly assigned to one of the two treatments: correction with single-vision spectacle lenses or correction with bifocal lenses having a +1.50 D add in a flattop segment. The average degree of myopia at baseline was -2.31 D (SD = 1.31 D). CONCLUSION: This clinical trial can be expected to determine the effectiveness of bifocal glasses in slowing the progression of myopia in children with nearpoint esophoria.

Child↗

PubMed1993

Biomechanical considerations in high myopia: Part III--Therapy for high myopia.

Clinical procedures for the treatment of high myopia are updated in this third part of a report on high myopia. After a discussion of testing techniques and refractive approaches for high myopia, an examination of therapeutic drug experiences shows their relative merits. The author believes that more investigation of beta blocker and epinephrine topical solutions is needed pertaining to the treatment of high myopia. Theoretically, such agents could improve deficient arterial perfusion of the highly myopic eye, and could be helpful in retarding scleral creep. Lifestyle recommendations include patient advice on accommodative reduction and proper exercise techniques. Low impact aerobics may have merit for highly myopic patients since the improved cardiovascular efficiency they can provide may improve the deficient arterial perfusion of their retinas. A summary of the three-part report on high myopia concludes the article. The physiological patterns of high myopia dovetail into the biomechanical considerations showing that a scleral pathogenesis hypothesis of myopic development is a viable working theory. The author's clinical procedures reflect the influence of that theory. If research were redirected from deprivation studies to investigating biomechanical considerations and pharmacological approaches to high myopia, the author contends that dramatically improved treatment regimens could result.

Biomechanical Phenomena↗

PubMed1995

Myopia in teenagers. An eight-year follow-up study on myopia progression and risk factors.

UNLABELLED: A prospective 2-year study on myopia progression was commenced in 1984/85, with special attention to the rate of progression in a representative group of school children aged 9 to 12 years. A follow-up investigation of this group of myopic persons (now aged 17-20 years) was performed after 8 years, in order to describe the refractive error and possible risk factors for myopia progression over the period. The refractive error increased from -2.77 D to -5.14 D (mean values). PARAMETERS: age at début, degree of myopia, intraocular pressure, changes at the fundus, status of phoria, nearpoint of convergence and accommodation were all measured at the start and related to the refractive error measured 8 years later. No single parameter, apart from age at début, indicated that the individual would reach a high degree of myopia. The refractive error among the children with a début below 7 years of age was -6.60 D, but only -3.72 D among those with a début after 10 years. The change in refractive error over the 8-year period was not statistically related to the age at début, neither did the rate of progression depend on the degree of myopia, the changes at the fundus, nor the intraocular pressure. However, children could be found who had a high rate of progression, by using a combination of these parameters.

Accommodation, Ocular↗

PubMed1986

Myopia and diabetes mellitus with special reference to adult-onset myopia.

A significant preponderance of myopia has been reported in adult Danish diabetics as compared to non-diabetics. This suggestion of a special type of diabetic myopia is evaluated in the present study. Comparing myopia pattern (degree and age at onset) in diabetics and non-diabetics, 80 of each, the assessment is based mainly on personal information about refractive history, gained through interviews of patients referred from other departments for routine eye examination. With a concise memory as inclusion criterion, the resulting sample is hardly representative, and the significant findings are to be considered tendencies only. In the whole sample there were more cases of late myopia onset and progression than expected from textbooks; 31% were of adult onset, i.e. after the age of 20 year. Most late-onset cases were of a low order, a type more prevalent in diabetics (40%) than in the non-diabetic controls (22.5%). Otherwise there was no indication of a special type of diabetic myopia.

Adult↗

PubMedDate not supplied

Surgical correction of high myopia in phakic eyes with Worst-Fechner myopia intraocular lenses.

BACKGROUND: Implanting an anterior chamber intraocular lens in a phakic eye is an effective surgical procedure for the correction of high myopia. However, the potential risks on the anterior segment structures are not well-known. We conducted a prospective study to evaluate the effectiveness, predictability, and safety after Worst-Fechner lenses were implanted to correct high myopia. METHODS: We studied 32 eyes with preoperative myopia from -9.50 to -27.00 diopters (D) (-16.60 +/- 6.29 D). All 32 eyes were studied by clinical specular microscopy, and the endothelium was analyzed for cell density. Twenty eyes were additionally examined by fluorophotometry for lens transmittance changes. Thirty eyes were additionally examined using the flare mode of a laser flare cell photometer for anterior chamber inflammation; the patients were divided into three subgroups of ten eyes each according to when the postoperative flare measurements were done: 12 months, 18 months, and 24 months. Thirteen phakic eyes with myopia greater than -6.00 D were used as a control group for the flare study. The mean follow-up was 18.3 +/- 8 months (range 6 to 24 mo). RESULTS: Fifty-seven per cent of eyes (16 of 28) had an uncorrected visual acuity of 20/40 or better 12 months after surgery, and 58% (10 of 17 eyes) at 24 months. Spectacle-corrected visual acuity improved: 0.15 at 12 months and 0.16 at 24 months (0.1 = one line) from preoperative values. Visual acuity was stable after 3 months. Eighty per cent of eyes (25 of 31) at 6 months, 75% (21 of 28) at 12 months, and 76.5% (13 of 17) at 24 months had been correctly planned to within +/-1.00 D of emmetropia. The refractive results were stable 3 months after surgery. The mean endothelial cell loss was 7.2% at 3 months, 10.6% at 6 months, 13% at 12 months, and 17.6% at 24 months after surgery. The mean lens transmittance loss was 0.62% at 3 months, 0.72% at 6 months, 0.82% at 12 months, and 1.03% at 18 months after surgery. Flare values were significantly higher for eyes implanted with Worst-Fechner lenses than were those of the control group in all periods under consideration (Mann-Whitney test, p < 0.05). A decentration greater than 0.5 mm was present in 43% of eyes (14 of 32), and halos in 56% (18 of 32). In three eyes (9.3%), fixation of the lens to the iris was not stable. CONCLUSIONS: Our results for the Worst-Fechner myopia lens confirm earlier findings on the effectiveness of the refractive results. However, our study showed a continual decrease in endothelial cell density, a decrease in lens transmittance, and a chronic subclinical inflammation after the implantation of these lenses. Moreover, decentration was common, and the fixation of the IOL to the iris was not stable in some eyes.

Adult↗

PubMed2000

U.S. clinical investigation of the Artisan myopia lens for the correction of high myopia in phakic eyes. Report of the results of phases 1 and 2, and interim phase 3.

PURPOSE: The purpose of this article is to present the results of the U.S. Clinical investigation of the Artisan anterior chamber iris fixed lens implant for the correction of myopia in phakic eyes. METHODS: A prospective, multi-center, FDA-supervised trial was designed and undertaken in the United States by Ophtec USA, Inc., Boca Raton, Florida to determine the safety and efficacy of the Artisan lens as a potential refractive treatment for patients with high myopia. During the trial, two different models of the Artisan lens were used: one with a 5-mm optical zone (model 206) and the other with a 6-mm optical zone (model 204). RESULTS: The data presented comprise 176 enrolled subjects and 264 implant procedures. The most frequently chosen Artisan lens power was -13.00 D (average, -12.76 D; SD, 3.24). The postoperative results at 6 months for all eyes (n = 135) showed 100% of patients were 20/40 or better best-corrected while 72% gained one or more lines and 22% gained two or more lines regardless of degree of astigmatism or postoperative goal. Through the course of the study, intraocular pressure maintained a level with a mean below 16 mmHg. In general, total reported complications in the patient cohort decreased over time, dropping from 39% at the initial visit to 10% at visit four and 0% at visit seven. CONCLUSIONS: On the basis of the interim results of the U.S. Clinical Investigation of the Artisan Myopia Lens for the Correction of High Myopia in Phakic Eyes, the Artisan anterior chamber phakic IOL may offer an option for correction of high degrees of myopia. Refractive outcomes were exceptional and complications were minimal and amenable to treatment.

Adult↗

PubMed1993

Biomechanical considerations of high myopia: Part II--Biomechanical forces affecting high myopia.

Assuming the possibility of a scleral pathogenesis hypothesis for the development of high myopia, an examination of biomechanical forces affecting myopic eyes is presented. The biomechanical considerations include Laplace's law applied to the eye, balloon expansion dynamics, and the "porthole" effect derived from mechanical engineering principles. Other biomechanical considerations include Coleman's pressure head theory of accommodation, extraocular muscle stresses, and the role of uveoscleral outflow. Balloon expansion dynamics cast doubt on the common usage of Laplace's law governing fluid filled spheres for estimating coat stresses in myopia. Coleman's theory of accommodation, featuring an accommodation induced pressure head between the anterior and vitreous chambers is reanalyzed. Experimental testing of this hypothesis is still lacking. Uveoscleral outflow computations show that the vitreous chamber distension of high myopia may dramatically increase the importance of uveoscleral outflow in the pressure dynamics of high myopia. These biomechanical force phenomena clearly provide fertile ground for several areas of research that could illuminate the great puzzles of myopia.

Accommodation, Ocular↗

PubMed2002

Undercorrection of myopia enhances rather than inhibits myopia progression.

The effect of myopic defocus on myopia progression was assessed in a two-year prospective study on 94 myopes aged 9-14 years, randomly allocated to an undercorrected group or a fully corrected control group. The 47 experimental subjects were blurred by approximately +0.75 D (blurring VA to 6/12), while the controls were fully corrected. Undercorrection produced more rapid myopia progression and axial elongation (ANOVA, F(1,374)=14.32, p<0.01). Contrary to animal studies, myopic defocus speeds up myopia development in already myopic humans. Myopia could be caused by a failure to detect the direction of defocus rather than by a mechanism exhibiting a zero-point error.

Adolescent↗

PubMed1980

[Documents on the origins of myopia. Fourth communication: Cause of myopia and some new perspectives in prevention and treatment (author's transl)].

The author's study of the literature and his own investigations have led him to develop a new theory of the origins of myopia. There are three principal causal factors: 1. close-range vision--weakened accommodation; 2. hereditary conditions; 3. weakened sclera--intraocular pressure. Even at the onset of development of myopia there is a complex interaction between the first two factors, which are involved more or less deeply. The third factor, the weakened sclera, only makes itself felt in more advanced stages of myopia. Two possibilities for prophylaxis and treatment may be inferred from these theories of the pathogenesis of myopia, namely influencing accommodation and surgical measures to strengthen the posterior pole. In addition, it is now possible to evaluate and apply some traditional treatment methods correctly.

Accommodation, Ocular↗

PubMedDate not supplied

Correction of high myopia with the Worst myopia claw intraocular lens.

BACKGROUND: Phakic anterior chamber lenses is one of the modalities used to correct high myopia. We report the initial results of our prospective study on the Worst myopia claw intraocular lens (IOL) that is fixated to the anterior iris. METHODS: We studied 35 eyes in 18 patients with a preoperative myopia ranging from -6.00 to -28.00 diopters (D). The follow up ranged from 6 months (n = 15) to 12 months (n = 20). RESULTS: In 26 (74.3%) eyes, the postoperative spherical equivalent refractive error was within 1.00 D of emmetropia. The mean refraction was stable between 1 to 2 months and 12 months. The mean spectacle-corrected visual acuity improved from 20/50 to 20/40. The straylight measurements did not show a significant increase postoperatively (p = .64). The mean endothelial cell loss was 5.6% (range, +6.3% to -22.6%) at 6 months, and 8.9% (range, +0.77% to -23.5%) at 12 months. We did not encounter major complications. CONCLUSION: Implanting a Worst myopia claw IOL in high myopic eyes resulted in a stable, reasonably accurate refractive outcome. This group of patients will be followed longer because of concern over ocular complications with this technique.

Adolescent↗

PubMed1998

Effect of parental myopia on the development of myopia in Hong Kong Chinese.

A representative sample of Hong Kong Chinese children was followed from 7 to 12 years of age. Refractive error was measured every year (n = 123 at age 7 years and n = 83 at age 12 years), the axial length of the eye was measured at age 12 years (n = 81) and the refractive status of the parents was also determined. Thirty-one percent of the parents in the sample were myopic and at the age of 12 years 53% of the children were myopic. There was no association between the refractive status of the parents and whether or not a child had myopia. The probability of a 12-year-old child with early-onset myopia having at least one myopic parent was 0.55 and the probability of myopic parents having a myopic child was 0.6. There was no difference in the refractive error or the axial length of 12-year-old children according to whether neither, one or both parents were myopic. The genetic influence on myopia may be different in Caucasian and Chinese children, although it is also possible that non-expression of the genotype in the parents may have confounded the determination of the inheritance pattern of myopia in Hong Kong Chinese children.

Adolescent↗

PubMed1993

[Severe myopia or myopia-disease?].

An increased axial length over 26 mm is one of the characteristics of highly myopic eyes. High myopia represents a marked type of the refraction disorders in which distance vision is impaired and leads to wear glasses in childhood. But this high myopia is also a degenerative myopia due to the distension of the whole envelopes of the ocular bulb mainly at the posterior part of it. Prevalence of high myopia in the general population ranges from 1 to 4%. The disease is usually inherited and transmitted in a dominant fashion. Degenerative myopic eyes are potentially blind eyes due to many complications occurring during lifetime at the choroidal or retinal level. Vision threatening retinal detachments are frequent and severe, and are sometimes related to a macular hole. Other diseases including glaucoma and cataract are more frequently encountered in those eyes but may be managed with higher success. Specific oculo-motor disturbances and strabismus are also encountered. At present, the main risk threatening central vision is macular disease with lacquer cracks and hemorrhages associated with subretinal new vessels growth. Only laser photocoagulation can halt the progression of the disease and avoid or delay severe loss of central vision.

Adolescent↗

PubMed1997

Retinal function with lens-induced myopia compared with form-deprivation myopia in chicks.

BACKGROUND: The retina is known to be involved in the development of form-deprivation myopia (FDM); however, it is not clear whether the retinal changes that lead to lens-induced myopia (LIM) are the same as those involved in FDM. To gain insight into the retinal mechanism(s) that cause myopia, we investigated differences in the results of electroretinography (ERG) in eyes with FDM and LIM. METHODS: LIM or FDM was induced in chick eyes by placing various powers of spectacles or an occluder over the left eyes of 6-day-old chicks. After 6 days, the spectacles or occluder was removed, refraction and axial length were measured and ERG was performed. Results for eyes treated with spectacles and those treated with occluders were compared. RESULTS: Refraction and axial length changed concomitant with the power of the lens used, but components of the ERG of eyes with LIM were not related to the power of lens added. Refraction and axial lengths of eyes covered with a -16 D lens did not differ from these values in eyes covered with an occluder. The a- and b-waves were also similar for the two groups. However, oscillatory potentials decreased significantly in the chicks with FDM. CONCLUSIONS: Retinal function differs in LIM and FDM, as indicated by differences in the oscillatory potentials. This difference may stem from the fact that in FDM the retinal image is continuously defocused, whereas images are ultimately focused on the retina in LIM.

Animals↗

PubMed1997

[Outcome of cataract operation with reduction of myopia in myopia magna].

UNLABELLED: Patients with high myopia represent a risk group in cataract surgery. They are suspected of having a higher incidence of retina problems after cataract surgery. In addition, IOL calculations may be difficult. METHOD: In a retrospective study data of 97 eyes of 60 high myopic patients were analyzed. The inclusion criterion was an axial length of > 26 mm. All eyes underwent cataract extraction and PC IOL implantation between 1991 and 1995. Evaluation focused on visual outcome, precision of the IOL power calculation and the rate of complications. RESULTS: Visual acuity increased from 0.18 to 0.46 postoperatively. On average, myopia was reduced from -13.6 D to -3.0 D;66% of the patients were +/-1 D;86% were +/-2 D within the predicted calculation of postoperative refraction. During a follow-up period of 14.8 months no retinal detachment occurred. CONCLUSION: Cataract extraction and IOL implantation showed good functional results, and prediction of postoperative refraction was satisfactory. Our data support the studies reporting a low incidence of retinal problems in patients with high myopia.

Aged↗

PubMed1999

Experimental animal myopia models are applicable to human juvenile-onset myopia.

Landmark explorations by Hubel and Wiesel investigating the importance of visual impressions in postnatal development of the visual system demonstrated that neural connections and eye growth can be affected by the absence of a clear retinal image during a critical period of postnatal development. Fundamental theories on neural plasticity and deprivation have recently been established that presume that a reduced quality of the retinal image during infancy and early childhood triggers an elongation of the posterior chamber of the eye, a so-called form deprivation myopia (FDM). In a retrospective multicenter study of 187 patients who suffered from phlyctenular keratitis with corneal opacification since early childhood, we reviewed data on gender, year and age at onset of the disease, refraction, and ultrasound biometry. Compared with the average refraction of +0.5 diopter (D) found in the general population, the mean refraction of -4.43 D that we found in our study demonstrated a marked shift toward myopia of almost 5 D. Patients with an early onset of phlyctenular keratitis had considerably higher myopia (-6.68 D) than those with a late onset (-1.67 D). Additionally, an axial elongation was confirmed by ultrasound biometry. Our average, axial length was 26.53 mm, compared with the epidemiologic mean of 24.00 mm. This myopic shift of 2.53 mm was caused mainly by an enlarged vitreous cavity. These results support the finding that blur can affect eye growth and lead to FDM not only in animal experiments but also in human beings.

Age of Onset↗