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PubMed2006

Effects of direct intravitreal dopamine injections on the development of lid-suture induced myopia in rabbits.

BACKGROUND: Dopamine (DA) storage and release are reduced in form deprivation myopia (FDM) in a wide range of species, from chicks to primates. FDM can be prevented by treatment with DA agonists such as apomorphine, and paradoxically by the dopamine neurotoxin 6-hydroxydopamine. In this study, we increased the DA levels by direct intravitreal DA injections to learn if FDM can be suppressed in a rabbit model. METHODS: Seven-day-old rabbits were deprived of pattern vision by the suturing the right eyelids after natural eye opening. In the first group (FD, n=20), the right eye received form deprivation (FD) alone. In the second group (DA-FD, n=16), the deprived eye of 7-day-old rabbits received four intravitreal injections of 20 microg dopamine every 5 days. In the third group (saline-FD, n=16), the deprived eye received saline injections with the same schedule. The contralateral eye remained untreated as a control. At the end of the 8-week deprivation period, the effects of DA on refractive error, corneal curvature and ocular dimensions were assessed by streak retinoscopy, keratometry and A-scan ultrasonography, respectively. RESULTS: Eight weeks of FDM induced a myopic shift of -2.70+/-0.87 D (n=20) in treated eyes compared with contralateral eyes. The major structural correlate of the myopia appeared to be elongation of the vitreous chamber (0.7+/-0.3 mm, n=20) and axial elongation (0.9+/-0.3 mm, n=20), respectively. Repeated intravitreal injections of DA fully prevented the myopic shift (-0.06+/-0.37 D), elongation of the vitreous chamber (0.1+/-0.3 mm, n=16) and axial elongation (0.3+/-0.2 mm, n=16) due to lid suture, whereas saline injections had slight effect. CONCLUSIONS: FD by suturing eyelids is an effective technique to induce a significant myopic shift, vitreous chamber and axial elongation in rabbits as a model of myopia development. These changes associated with FD were retarded by intravitreal injections of DA.

Animals↗

PubMed2006

Keratocyte density in the retroablation area after LASEK for the correction of myopia.

PURPOSE: During excimer laser photoablation keratocyte cell death is induced in the retroablation area. Afterwards this area is repopulated by keratocyte mitosis and migration from the adjacent stroma. The aim of this study was to investigate keratocyte density in the retroablation area and in the posterior stroma during the first year after LASEK for the correction of myopia. METHODS: In a prospective study LASEK surgery was performed in 17 eyes of 10 consecutive patients for the correction of myopia (-2.25 D to -9.0 D, mean -5.0 D). Confocal microscopy (Nidek Confoscan 2) was performed before surgery and 1 month, 3 months, 6 months and 12 months after LASEK. Keratocyte density was assessed in the anterior retroablation area at depths of 5 mum and 25 mum and in the posterior stroma at distances of 5 mum and 100 mum from the corneal endothelium and compared with the corresponding area before surgery. RESULTS: Keratocyte density was statistically significant reduced in the retroablation area at all timepoints after LASEK. At a depth of 5 mum, cell densities were decreased by 64%, 47%, 43%, and 28% at 1 month, 3 months, 6 months and 12 months after LASEK compared with preoperative values. At a depth of 25 mum, cell densities were decreased by 51%, 32%, 28%, and 18% at 1 month, 3 months, 6 months and 12 months after LASEK compared with preoperative values. In the posterior stroma no significant change in keratocyte density was observed at any time after LASEK. CONCLUSIONS: Keratocyte density in the anterior retroablation area recovers during the first year after LASEK for the correction of myopia, but does not go back to preoperative values.

Adult↗

PubMed1998

Lacquer crack lesions in experimental chick myopia.

BACKGROUND: Lacquer crack lesion (LCL) is a complication of human pathologic myopia, accompanied by loss of retinal pigment epithelium (RPE) and break of Bruch's membrane. The present paper describes comparable lesions occurring in prolonged experimental myopia in the chick. METHODS: Form-deprivation myopia was induced by unilateral eyelid suturing on the 1st day after hatching. Bruch's membrane in NaOH hydrolyzed preparations and vascular corrosion casts of the choroidal vasculature were examined with scanning electron microscopy. Histological changes in the retina and choroid were also examined with light and transmission electron microscopy. RESULTS: Pale and linear lesions were found in the myopic chick eyes at the age of 8 weeks. In the lesion area, Bruch's membrane was totally broken up and the network of choriocapillaries was totally ruptured with highly atrophied marginal capillaries. The retina was continuous, but was depressed to form a groove in the lesion with the apparently intact inner retina and degenerated photoreceptor cells. Attenuated fibroblasts encompassed the outer circumference of the lesion. RPE cells were scattered in the tissue space inside the fibroblastic investment and also in the choroidal stroma without their polarity. CONCLUSION: The formation of LCL was suggested to be a result of passive stretch exerted upon Bruch's membrane and the capillary network due to abnormal enlargement of the myopic eyes. These results may promote further understanding of the mechanism regarding the development of human lacquer cracks.

Animals↗

PubMed1999

PRK-induced anisometropia in the rabbit as a model of myopia.

BACKGROUND: Current animal models of myopia, such as the chick and the tree shrew, have characteristics that limit their applicability to human myopia and/or their use among researchers. The purpose of this study was to establish a rabbit model of myopia based on photorefractive keratectomy (PRK)-induced anisometropia. METHODS: A group of five pigmented rabbits was treated with a monocular -5 D PRK at 5 weeks of age. At 10 weeks of age, two of the eyes were retreated with a second -5 D PRK procedure to compensate for partial regression of the refractive effect. A second group of six pigmented rabbits was treated with a monocular -6 D PRK at 10 weeks of age. Longitudinal measurements of corneal curvature, refraction, and axial length were performed until the rabbits were 13 and 21 weeks of age in groups 1 and 2, respectively. The rabbits in each group were from the same litter. RESULTS: Keratometry and retinoscopy measurements confirmed the refractive effect of the PRK procedures. At the final measurement point in group 1, the PRK-treated eyes were significantly longer than the untreated eyes (16.01 +/- 0.45 mm vs 15.45 +/- 0.56 mm). In group 2, the PRK-treated eyes were significantly longer by 0.19 mm and 0.20 mm at ages 19 and 21 weeks, respectively. CONCLUSIONS: PRK-induced anisometropia is an effective technique to induce hyperopic error compensation in the rabbit as a model of myopic development. The technique is effective if the PRK procedure is performed at either 5 or 10 weeks of age. However, after PRK at 5 weeks of age, partial retreatment may be necessary due to regression of the PRK effect.

Animals↗

PubMed1999

Surgical removal of subfoveal choroidal neovascular membranes in high myopia.

BACKGROUND: A study was carried out to elucidate the anatomical and functional outcome after surgical excision of subfoveal choroidal neovascular membranes in high myopia. METHODS: Sixty-five patients with high myopia (> or =6 diopters), well-defined subfoveal neovascular membranes on fluorescein angiography and preoperative visual acuity < or =20/100 were selected for surgery. A standardized surgical technique was used in all cases, by a single surgeon. The main outcomes assessed were Snellen visual acuity, surgical retinal pigment epithelium defect and postoperative perfusion of the choriocapillaris. Multifactor analysis of variance and chi-square/Fisher's exact test statistics were used to assess the association between patients' pre- and postoperative characteristics and outcome measures. RESULTS: Follow-up ranged from 6 to 48 months (mean 16 months). Mean postoperative visual acuity (0.18) was significantly better than mean preoperative visual acuity (0.09). Visual acuity improved by at least two lines in 29 eyes (45%) and was unchanged in 24 (37%). Overall, 43 eyes (66%) had visual acuity of 20/200 or better and 15 (23%), 20/60 or better. Predictive factors with a significant effect on final visual acuity were mean visual acuity, preoperative status of retinal pigment epithelium and postoperative perfusion of the choriocapillaris. Postoperative perfusion was detected in 31 (48%) of the total 65 eyes and in 12 (67%) of the 18 eyes with normal retinal pigment epithelium at baseline. The mean postoperative retinal pigment epithelium defect was 4.6 times larger than the original neovascular membrane. In selected patients, SLO macular scotometry showed areas of retained retinal sensitivity within the atrophic scar. CONCLUSION: The natural history of subfoveal neovascularization in high myopia is rarely visually restorative. By contrast, surgical excision of the membranes is feasible and may restore visual acuity in selected patients. This therapeutic approach merits a formal multicenter clinical trial.

Adolescent↗

PubMedDate not supplied

Myopia control trial with progressive addition lenses in Japanese schoolchildren: baseline measures of refraction, accommodation, and heterophoria.

PURPOSE: To describe baseline measures of refraction, accommodation, and heterophoria in Japanese schoolchildren enrolled in a randomized clinical trial that examines whether progressive addition lenses slow myopic progression compared with single-focus lenses. METHODS: Ninety-five children with myopia between -1.25 and -6.00 D spherical equivalent were recruited. Their ages ranged from 6 to 12 years; 46% were girls. The main outcome measure for the trial was progression of myopia determined by cycloplegic (0.5% tropicamide) autorefraction. Accommodative lags and heterophoria were also evaluated. RESULTS: Because data were similar in both eyes, they are reported for the right eye only. The mean (+/-SD) cycloplegic autorefraction (spherical equivalent) was -3.22 +/- 1.22 D. The cycloplegic subjective refraction was larger (less myopic) than the noncycloplegic subjective refraction by 0.25 +/- 0.22 D. The mean distance prescription was larger (undercorrection) than the mean cycloplegic autorefraction by 0.74 +/- 0.37 D. The mean accommodative lag for a 4.74 D target was 2.05 +/- 0.98 D. Near-point esophoria was found in 29 (31%) of the children when their refractive errors were fully corrected with glasses. CONCLUSIONS: The measurements reported herein will serve as a basis for assessing changes that occur over a 3-year follow-up period. Compared with the baseline measurements in the Correction of Myopia Evaluation Trial, clear differences were observed in the mean cycloplegic autorefraction and distance prescriptions. The accommodation and heterophoria data showed characteristics similar to those recently reported in myopic children abroad.

Accommodation, Ocular↗

PubMed2005

Artisan phakic intraocular lens for correcting high myopia.

OBJECTIVES: To evaluate the safety indexes and efficacy of Artisan phakic intraocular lens (IOL) for the correction of high myopia. METHODS: Retrospective interventional case series reports. Thirty-one eyes (22 patients) with myopia from -5.25 to -19.00 diopters underwent implantation of an Artisan phakic IOL. Follow-up examinations were performed at 1 day, 1 week, 1 month, and 3 months. The following parameters were recorded: manifest refraction, slit-lamp examination, applanation tonometry, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), complications or adverse reactions. The primary variable was the refractive outcome at 3 months. Secondary variables were change in BSCVA, and efficacy and safety indexes. RESULTS: At 3 months, mean spherical equivalent was -0.50 +/- 0.36 diopters (range, -1.25 - plano). In 29 eyes (93.5%) UCVA was 6/12 or better; the other three eyes had UCVA of 6/15. The difference between preoperative and 1 week postoperative BSCVA was not statistically significant (p = 0.25). Comparison of BSCVA at 1 week and at 1 month was statistically significant (p = 0.05); this difference was even more significant at 3 months (p = 0.01). The BSCVA remained the same or improved for all the eyes. BSCVA for 20 eyes (64.5%) had improved one or more lines in visual acuity. Mean endothelial cell loss at 3 months was 3.96%. CONCLUSION: The Artisan lens is a safe, predictable, and efficacious method to correct high myopia. Postoperative gain in BSCVA was achieved for the majority of eyes. Future study to assess safety indexes and risk of complications is required with long-term follow-up.

Adult↗

PubMed1981

Pathologic myopia and choroidal neovascularization.

In 14 of 27 eyes with choroidal neovascular membranes associated with severe myopia, visual acuity deteriorated two or more lines on the Snellen chart. Twelve of the 27 eyes became legally blind. Final visual acuity may be related to the position of the neovascular membrane within the posterior pole. Four of the eight eyes with new vessels outside of the foveal avascular zone had follow-up visual acuities of 6/12 (20/40) or better. Only one of five eyes with new vessels extending to the edge of the avascular zone had a final visual acuity of 6/12 (20/40) or better. Three of 14 eyes with a neovascular membrane beneath the foveal avascular zone had visual acuities of 6/12 (20/40) or better. Neovascularization associated with severe myopia clearly jeopardizes central visual acuity. Laser photocoagulation therapy may be useful in treating neovascular membranes outside the foveal avascular zone or extending to the edge of the perifoveal capillary network. A larger prospective study is needed to determine the guidelines for and efficacy of such treatment for patients with severe myopia who develop choroidal neovascularization.

Adult↗

PubMed1981

Monocular axial myopia associated with neonatal eyelid closure in human infants.

We studied eight infants who developed unilateral axial myopia associated with neonatal eyelid closure. Clinical findings and ultrasonographic biometric measurements suggested that axial elongation of the eye may occur as a result of neonatal eyelid closure, a finding similar to that for experimental myopia produced in neonatal animals after eyelid fusion. Early treatment of eyelid occlusion in the neonate may prevent axial myopia and subsequent anisometropic amblyopia.

Blepharoptosis↗

PubMed1984

Transient myopia and accommodative paresis following retinal cryotherapy and panretinal photocoagulation.

Loss of accommodation, transient myopia, or both, were complications following retinal cryotherapy in two eyes and after panretinal photocoagulation in six eyes (seven patients). A 17-year-old young man had these refractive difficulties one week after cryotherapy for retinal holes. His accommodative amplitude measured 1.0 D in the treated eye and 8.0 D in the untreated eye. One week later he received cryotherapy to the previously untreated eye, reducing that accommodative amplitude to 2.5 D. Accommodative paresis and transient myopia resolved without treatment within five weeks. Six other patients (six eyes, seven episodes) with an average age of 33 years demonstrated accommodative loss (40% to 92% decrease, average decrease 64%), transient myopia, or both, after panretinal photocoagulation for proliferative diabetic retinopathy. All patients recovered without treatment within six weeks (average, 22 days). All young patients should be made aware of this transient, but troublesome complication before treatment.

Accommodation, Ocular↗

PubMed1986

Influence of HLA-DR phenotype and myopia on the risk of nonproliferative and proliferative diabetic retinopathy.

The relationship between HLA-DR phenotype, refractive error, and risk of both nonproliferative and proliferative diabetic retinopathy was studied among 227 insulin-dependent diabetics participating in a case-control study of diabetic retinopathy. In the absence of myopia, risk of both proliferative and nonproliferative diabetic retinopathy was increased for HLA-DR phenotypes 4/0, 3/0, and X/X (HLA susceptible) compared to HLA-DR phenotypes 3/4, 3/X, and 4/X (HLA nonsusceptible). Odds ratios equalled 11.8 and 7.4 respectively. In the presence of myopia this increased risk associated with HLA status was abolished. Myopia decreased the risk of proliferative and nonproliferative diabetic retinopathy among HLA-susceptible individuals, odds ratio equalled .09 and .09, but had no protective influence among HLA-nonsusceptible individuals.

Aged↗

PubMed1989

Lipid peroxidation and human cataractogenesis in diabetes and severe myopia.

To investigate the role of lipid peroxidation in human cataract, malondialdehyde, a breakdown product of lipid peroxidation, was measured in clear and cataractous lenses from normal subjects, and in cataractous lenses from diabetics and from subjects with severe myopia. The cataractous lenses contained more malondialdehyde than did clear lenses and the level was higher in diabetes and severe myopia than in the idiopathic forms. This indicates that lipid peroxidation may be involved in the development of senile cataract and, as a direct consequence of retinal damage, also in the pathogenesis of cataract in diabetes and in severe myopia.

Adult↗

PubMed1987

Developmental aspects of experimental myopia in chicks: susceptibility, recovery and relation to emmetropization.

Chicks deprived of form-vision in the lateral part of their visual fields become severely myopic largely because of elongation of the vitreous chamber. The myopia mostly affects the visually deprived nasal retina; the nondeprived temporal retina is unaffected. These changes occur most rapidly early in life, being evident then after only 3 days of visual restriction. The susceptibility declines with age, being proportional to the rate of increase of axial length. Recovery from this myopia occurs if the visual restriction is removed during the first 6 weeks of life, as a result of the cessation of elongation of the vitreous chamber. The rate of recovery is directly related to the degree of myopia and inversely related to age. The pattern of changes in refractive status and variability argue for the probable existence of an active mechanism regulating eye growth in a manner dependent on refractive error, thereby producing emmetropization.

Accommodation, Ocular↗

PubMed1995

The duration of normal visual exposure necessary to prevent form deprivation myopia in chicks.

The aim of this study was to determine the minimum daily period of exposure to normal visual stimulation required to prevent occlusion induced myopia in chicks. Chicks were treated with monocular translucent occlusion in a 12 hr light/12 hr dark cycle. Occluders were removed for 0 (constant occlusion), 15, 20, 30, 40, 60, 75, 90, 120, 150, 240 or 720 (no occlusion) minutes each day for either 2 or 3 weeks. Fellow eyes and the eyes of normal chicks (bilaterally unoccluded) were used as controls. Occlusion-induced myopia and axial elongation were found to decrease significantly (P < 0.01) with increasing daily exposure to normal visual stimulation. Application of a time series equation to the data estimates that 30 and 130 min of normal visual exposure per day reduces myopia by 50 and 95% respectively. This study demonstrated that the regulation of ocular growth is affected strongly by short periods of normal visual stimulation in the presence of long periods of abnormal stimulation.

Animals↗

PubMed1995

A role for photoreceptor outer segments in the induction of deprivation myopia.

An ultrastructural examination of the outer retina and choroid of hatchling chicks reared for periods of 1, 2 or 4 weeks with opaque occluders (MD) covering one eye, was instigated to elucidate the mechanism of deprivation myopia. Refractive myopia (approximately 20 D), retinal and choroidal thinning were induced in all deprived eyes. Electron microscopy showed significant changes in the MD eyes compared to normals. Cone inner segments were markedly thicker and outer segment lamellae more damaged. The rod outer segments were elongated and thicker than normal, such that their distal tips either directly apposed the basal lamina of the retinal pigment epithelium, or indented the cell nuclei. We hypothesize that this "rod-push" mechanism leads to thinning of the choroid in deprived eyes, and may directly contribute to axial myopia.

Animals↗

PubMed1995

Reduced extracellular matrix in mammalian sclera with induced myopia.

The purpose of this study was to learn whether visual form deprivation, which produces myopia in the deprived eye, alters the scleral extracellular matrix in tree shrew, a mammal closely related to primates. Axial myopia was induced in 10 tree shrews by monocular deprivation imposed with a translucent diffuser. The other eye in each animal was an untreated control. After 21 days of deprivation the refractive state and axial component dimensions were measured and the eyes were assayed for levels of DNA, hydroxyproline, and sulfated glycosaminoglycans (GAGs) in samples of the sclera and the cornea. In comparison to the open control eye, the deprived eyes became myopic and elongated. In the sclera, DNA levels were not significantly changed from the control eye. Sulfated GAG levels were significantly lower in the deprived eyes, as compared to the control eyes, at the posterior pole (-15.6%), at the nasal equatorial region (-18.1%), and in the rest of the sclera (-11.6%). The hydroxyproline level was significantly lower only at the posterior pole (-11.8%). Levels of sulfated GAGs were significantly reduced relative to DNA and relative to hydroxyproline in the total sclera. No significant changes were found in the cornea. The lower level of sulfated GAGs throughout the sclera of the deprived eyes, as compared with the control eyes, suggests that the deprived sclera contained less proteoglycan, or that the proteoglycans were less glycosylated or less sulfated. In contrast, the regional reduction of hydroxyproline suggests that collagen accumulation was specifically reduced only at the posterior pole of deprived eyes. These results suggest that form deprivation slows or reverses the normal process of extracellular matrix accumulation in the sclera of this mammal. This may allow the sclera to be more distensible, permitting the vitreous chamber elongation and resultant myopia.

Animals↗

PubMed2006

Functional outcome and patient satisfaction after Artisan phakic intraocular lens implantation for the correction of myopia.

PURPOSE: To determine patient satisfaction after Artisan phakic intraocular lens (PIOL) implantation to correct myopia. DESIGN: Non-comparative prospective case series. METHODS: One hundred twenty eyes of 60 patients who had undergone Artisan PIOL implantation to correct myopia were analyzed. A validated questionnaire that consisted of 66 satisfaction items were self-administered by patients 12 months after surgery. Clinical parameters (PIOL decentration, the difference between pupil size and PIOL optical zone, and optical aberrations) were measured. Main outcome measures of satisfaction scale scores (global satisfaction, quality of uncorrected and corrected vision, night vision, glare, day and night driving) were analyzed. Correlations with clinical parameters were obtained. RESULTS: After surgery, 98.3% of patients were satisfied, and 73.3% of patients considered their night vision to be the same or better; 44.1% of patients reported more bothersome glare. The night vision score correlated with spheric aberration (r = -0.303; P = .020). The glare score correlated with the difference between scotopic pupil size and PIOL optical zone (r = -0.280; P = .030) and vertical coma (r = -0.337; P = .009). The night driving score correlated with postoperative spheric equivalent (r = 0.375; P = .009), total root mean square aberrations (r = -0.337; P = .017), higher order root mean square aberrations (r = -0.313; P = .027), and vertical coma (r = -0.297; P = .036). CONCLUSION: Overall satisfaction after Artisan PIOL implantation for myopia is excellent. The quality of night vision and night driving were related to scotopic pupil size, individual higher order aberrations, and residual refractive error.

Adult↗

PubMed2006

Iris-supported phakic lenses (rigid vs foldable version) for treating moderately high myopia: randomized paired eye comparison.

PURPOSE: To compare refractive performance of Artisan (Ophtec, Groningen, The Netherlands) or Verisyse phakic intraocular lens and its foldable version, Artiflex (Ophtec), for the correction of moderately high myopia. DESIGN: Randomized pilot study. METHODS: setting: Institutional practice. patient population: Thirty-one patients with myopia that ranged from -6 to -14 diopters (D). interventional procedure: One eye was implanted with an Artisan phakic intraocular lens (PIOL) and the other with an Artiflex PIOLs. main outcome measures: Primary outcome measure was the percentage of eyes with uncorrected visual acuity (UCVA) of >20/40 at one year after the operation. Main secondary outcome measures were the safety index, the change of two lines or more of best spectacle-corrected visual acuity (BSCVA) and the endothelial cell count. RESULTS: No intraoperative complications were noticed. One year after surgery, the percentage of eyes with UCVA of >20/40 was 51.6% (16/31 patients) for Artisan-treated eyes and 77.4% (24/31 patients) for Artiflex-treated eyes (P = .033). One month after surgery, this same percentage was 42.9% (13/31 patients) and 77.4% (24/31 patients), respectively (P = .004). The safety index at one year was 1.13 +/- 0.24 for Artisan-treated eyes and 1.12 +/- 0.21 for Artiflex-treated eyes, which is a difference that was not statistically significant (P = 0.742). At one year after surgery, the changes of two lines or more of BSCVA and the endothelial cell loss were similar for both groups. CONCLUSION: To correct moderately high myopia, the Artiflex lens provides a faster visual recovery and a better UCVA than does the Artisan lens. The safety of the lens should be supported by an enlarged sample size and a longer follow-up period.

Adult↗