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PubMed1996

[An experimental study on effects of form deprivation on development of myopia].

OBJECTIVE: The study was designed to approach the pathogenesis of myopia. METHOD: Haisaik chickens were used to establish the animal models of myopia and form deprivation method was applied. Monocular eyelids were sutured for form deprivation on the 5th day after chicken birth. RESULTS: Form deprivation leads to myopic refractive abnormality (P < 0.001). The ocular anteroposterior axis (P < 0.005), transverse and vertical diameters lengthen (P < 0.05). In the mean time, obvious pathologic changes were found. The cartilaginous cell layer of the sclera became thicker, the numbers of chondrocytes and binucleate cells were greater, and the fibrous layer of the sclera was thinner. CONCLUSION: Form deprivation is the main cause of the development of myopia.

Animals↗
PubMed1995

[Excimer laser photorefractive keratectomy in myopia and astigmatism--1 year experience].

The authors evaluate the results of photorefractive keratectomy by means of an excimer laser myopia and astigmatism in 343 eyes with a minimal follow-up period of 9 months. The value of the preoperative refractive error expressed in spherical equivalents was -1,75 to -18,5 d. In astigmatism the maximal value was -5 cyl. d. The group was divided into four sub-groups: A) -1,75 to -3,0 d., B) -3,25 to -6,0 d., C) -6,25 to -10,0 d., D) more than -10,25 d. The spherical equivalent of the refractive error 9 month after operation was -0,28 d. in group A, -0,37 d. in group B, -0,67 d. in group C and -1,82 d. in group D. Uncorrected vision, 6/12 or better, 9 mons after operation was recorded in group A in 98,1% patients, group B 95,6% group C 91,2% and in group D in 72,5% patients. The authors proved a high effectiveness, safety predictability and stability of photorefractive keratectomy by means of an excimer laser in myopia up to -10 d. Photorefractive keratectomy is a promising method which extends the possibilities of correcting myopia and astigmatism in sufficiently positively motivated and indicated patients.

Adult↗
PubMed1996

[Use of contact lenses in children with severe myopia].

PURPOSE: To present own observation on the usefulness of soft contact lenses in treatment of high myopia in children and youth. MATERIAL AND METHODS: 43 children with high myopia were selected from 2320 patients fitted with lenses due to refraction errors. The whole complex of ophthalmological examinations including ultra sound scan of eyeballs and measurement of corneal sensitivity were performed prior to the lens fitting. Visual acuity and stereoscopy of glass and contact lenses were estimated. RESULTS: The contact lens fitting enabled to achieve significant visual acuity improvement in all patients. The improvement was observed in 53.4% patients in comparison with glass correction. Stereoscopy was achieved in 58.1% patients, with glass correction and 81.4% patients with contact lenses. CONCLUSIONS: Soft contact lenses are very useful in high myopia correction in growing-up patients. The basic and indispensable factor of successful contact lens fitting is a good cooperation with parents.

Adolescent↗
PubMed1997

Corneal topography and myopia. A cross-sectional study.

PURPOSE: Central corneal curvature is known to vary with refractive error, but the relation between corneal topography and ametropia is less clear. The current study was conducted to determine whether a relation exists between corneal asphericity and myopia. Associations between corneal asphericity and each of the components of refraction also were examined. METHODS: Corneal asphericity and apical radius of curvature were determined for 113 eyes (spherical equivalent refractive error +0.25 diopter [D] to -9.88 D) by fitting a conicoid equation to videokeratoscopic data. Computerized videokeratoscopic images were recorded using a Topographic Modeling System. Keratometry also was performed on each eye. Anterior chamber depth, lens thickness, vitreous chamber depth, and axial length were measured with a hand-held biometric ruler. RESULTS: A low but statistically significant positive correlation was found between corneal asphericity (Q) and spherical equivalent refractive error (r = 0.275, P < 0.01). Significant relations also were observed between Q and vitreous chamber depth (r = 0.17, P < 0.1) and between Q and axial length (r = 0.24, P < 0.05). The association between Q and corneal radius of curvature was found not to be significant. Eyes with higher levels of myopia had steeper central corneal curvatures, deeper anterior and vitreous chambers, and greater axial lengths. CONCLUSIONS: A tendency for the cornea to flatten less rapidly in the periphery with increasing myopia was shown. Decreased peripheral corneal flattening also was observed in association with increasing vitreous chamber depth and increasing axial length. These findings have implications for refractive surgery outcomes, schematic eye modeling, contact lens design, and ocular aberration analysis.

Adolescent↗
PubMed1997

Excimer laser photorefractive keratectomy for residual myopia after radial keratotomy.

OBJECTIVE: To evaluate the surgical outcome of excimer laser photorefractive keratectomy (PRK) for undercorrected myopia after radial keratotomy (RK). DESIGN: Case series. SETTING: Gimbel Eye Centre, Calgary. PATIENTS: Thirty-one patients (37 eyes) who underwent excimer laser PRK for residual myopia after RK and were followed for at least 12 months. OUTCOME MEASURES: Spherical equivalent refraction, uncorrected and best corrected Snellen visual acuity, attempted and achieved correction, and corneal haze. RESULTS: The mean refraction before PRK was -3.11 (standard deviation [SD] 1.48) dioptres and 12 months after PRK, -1.18 D (SD 1.48 D) (p < 0.0001). Twelve months after PRK 24 eyes (64.9%) had an uncorrected visual acuity of 20/40 or better. Five eyes lost one line of best corrected acuity, and one eye lost more than two lines. At 12 months 28 eyes (75.7%) had no corneal haze or trace haze, 8 (21.6%) had mild haze, and 1 (2.7%) had marked haze. CONCLUSIONS: Our results indicate that excimer laser PRK has the potential to manage undercorrection of myopia after RK. The issues of refractive predictability, loss of best corrected visual acuity and corneal haze require further study.

Adult↗
PubMedDate not supplied

[Biomechanical regularities in the distribution of tension in various topographic zones of the eyelids in children in health and myopia of different degree].

The authors assessed the method for life-time study of the biomechanical characteristics of ocular tissues in 281 children (562 eyes) aged 7 to 14 years. The method for assessing the biomechanics of the eyelids is described. In detail. The rates of propagation of acoustic waves in normal tissue and in 1.0 to 6.0 diopters myopia are presented. A correlation has been revealed between the increase of the velocity of acoustic surface waves, propagating in the horizontal direction in the internal segment of the orbital area of the upper eyelids, and the value of clinical refraction in myopia. The authors consider clinical signs of myopia-screwing up one's eyes and a wider lid slit-from a biomechanical viewpoint.

Adolescent↗
PubMedDate not supplied

[Quantum therapy in ophthalmology: therapy of progressive myopia by ASO devices].

Progressive myopia was treated by a novel method: quantum ophthalmotherapy. Highly effective drug-free treatment is based on the biorhythmical exposure of the organ of vision to low-intensive light at different wavelengths. The new method helps arrest the progress of myopia, restore the accommodation volume, and improve the vision acuity in at least 95% of patients. High efficacy and absence of complications confirmed by numerous cases recommend quantum ophthalmotherapy with ASO devices for the treatment of progressive myopia.

Accommodation, Ocular↗
PubMedDate not supplied

[Modern aspects of surgical treatment of myopia].

Problems in complex surgical treatment of myopia are discussed. Extensive clinical data and long follow-up of the patients permitted the authors to develop a well-based system of care which helps not only arrest the progress of myopia, but correct it within a rather wide range. The pathogenesis of tissue process in progressive myopia is discussed basing on the regularities revealed experimentally. The main modern operations on the cornea and sclera are described. Data on the inter-layer transplantation of the cornea, developed at the Chair of Ophthalmic Diseases of the Russian University of Peoples' Friendship are presented.

Adolescent↗
PubMed1997

Scleral reinforcement in progressive myopia and intraoperative ultrasound control of the cadaver fascia lata strip.

Scleral reinforcement (sustentaculum sclerae) is one of the operations against myopia. During the progression of myopia the eye grows. The chorioretinal layer can only moderately follow the expansion of the sclera, and mostly this is the cause of the complications that can cause permanent visual acuity decrease. The aim of the operation is to strengthen the posterior part of the sclera by implantation of a cadaver fascia lata strip, that slows down or stops the expansion of the eyeball, and this way prevents the development of complications. At our Department we perform the Snyder-Thompson technique. Between 1984 and 1994 343 operations were performed at our Department. We followed up the changes of the axial lengths by ultrasound (A-mode) examinations. The axial length decreased in 43.7% remained unchanged in 22.2% and increased in 34.1% of the cases. We controlled the location of the strip intra- and postoperatively with B-mode ultrasound. Nowadays scleral reinforcement is still the only possibility to stop or slow down the expansion of the eyeball in cases of progressive high myopia.

Cadaver↗
PubMed1997

Intrastromal corneal ring, a new refractive surgical technique to decrease myopia. Experimental and clinical results.

From among the wide range of keratorefractive operations, the authors applied the intrastromal corneal ring (ICR) technique to treat myopia. The results of operations performed on dogs' eyes were evaluated using slit lamp investigations, cornea topography and histological investigations. In the possession of favourable results, this kind of operation was successfully performed on three patients suffering from expressed unilateral myopia, too. The desired optical results (10.0 dioptres) proved to be permanent 3-10 months after surgery and were demonstrated by the patients' visual acuity as well as cornea topographic examinations. The surrounding of the PMMA ring situated intrastromally and the substance of the cornea remained calm and clear, respectively. The authors think that the ICR technique can successfully be applied in the treatment of myopia similarly to refractive surgical interventions such as radial keratotomy (RK) and excimer laser photorefractive keratectomy (PRK), which are widely used methods these days.

Animals↗
PubMed1997

Multifocal electroretinogram in myopia.

PURPOSE: To investigate early changes of retinal function in myopic eyes, patients with various degrees of myopia underwent multifocal electroretinography (multifocal ERG). METHODS: Thirty young patients (mean age, 26.1 years) were divided into three groups according to the degree of refractive error: emmetropia/low, medium, and high myopia. All groups were matched by sex and age. All subjects had good corrected visual acuities of better than 1.0 and normal color vision. No other ophthalmoscopic abnormalities except for tessellated fundus existed. Three grouping programs (all-traces, rings, and quadrants) were used, and all-traces grouping waveforms, six-ring grouping waveforms, and four-quadrant grouping waveforms were determined from 103 local responses. We studied the differences of amplitudes and latencies of the waves among the myopic groups and their relation to refractive error and axial length. RESULTS: Amplitudes were reduced and latencies were delayed as the refractive errors increased. The amplitudes in the peripheral areas were more reduced in the myopic groups. CONCLUSIONS: The reduced amplitude and delayed latency of each wave of multifocal ERG in myopia resulted primarily from cone function loss, which may occur even when the only noted retinal change is tessellated fundus.

Adult↗
PubMedDate not supplied

[Ophthalmic tone of myopic eyes: statistical evaluation and role in formation of acquired myopia].

The author summarizes the results of many-year profound statistical analysis of ophthalmic tone in myopic patients. Intraocular pressure (IOP) of myopic eyes in patients aged 10 to 62 years and refraction from 0.5 to -24.0 diopters was measured in 1220 eyes by the same type of Goldman's tonometer. Detailed distribution of IOP for age and refraction factor is presented. IOP has been studied in emmetropia, stable and progressive myopia, and in paired anisometropic eyes. The author emphasizes that myopia progresses at various levels of ophthalmic tone, whose increase is mainly functional and reversible, and is caused by organic changes in the anterior chamber angle in only 7% of cases. The author claims that IOP is an important characteristic of a myopic eye and is to be taken into consideration when prescribing pathogenetic therapy for progressive myopia.

Adolescent↗
PubMed1998

Conservative photorefractive keratectomy for residual myopia following radial keratotomy.

OBJECTIVE: To evaluate the efficacy, predictability, stability and safety of a conservative approach to photorefractive keratectomy (PRK) (treating only 60% to 70% of the residual myopia) for residual myopia following radial keratotomy (RK). DESIGN: Case series. SETTING: Laser eye surgery centre in Windsor, Ont. PATIENTS: Thirty-three eyes of 27 patients with an average age of 40.1 years who underwent PRK between January 1993 and July 1995, 12 months or more after RK. All were followed for at least 12 months after PRK. OUTCOME MEASURES: Efficacy and safety were assessed by changes in the uncorrected and best corrected visual acuity. Predictability was determined by the proximity of the final result to emmetropia. The stability of the refractive outcome was assessed over the follow-up period. RESULTS: At 12 months 12 eyes (36%) had 20/20 or better uncorrected visual acuity and 29 eyes (88%) had 20/40 or better uncorrected acuity. Twenty-seven eyes (82%) were within 0.50 D of emmetropia, and 30 eyes (91%) were within 1.00 D of emmetropia. There was a significant change in the mean postoperative spherical equivalent between 1 and 3 months (p < 0.001); however, there was no significant change after this time. Six eyes (18%) had a loss of 2 or more lines of best corrected visual acuity due to corneal haze; however, retreatment reduced this incidence to 9% at 12 months. CONCLUSIONS: Our results show that conservative PRK for residual myopia following RK is efficacious and predictable and produces stable results. However, the risk of postoperative haze reduces the safety of this procedure.

Adult↗
PubMed1998

Relation of childhood myopia progression rates to time of year.

BACKGROUND: One potential method for assessment of the effect of near work on childhood myopia progression is to compare progression rates overtime spans that have differing near-point demands. METHODS: Myopia progression rates were calculated for a 6-month period during the school year (called school rate in this article) and for a 6-month period that included the 3 months of summer vacation (called summer rate). Data used for analysis were right eye spherical equivalents from manifest subjective refractions of 27 children in a longitudinal study at Northeastern State University in Oklahoma, and 15 children in a longitudinal study at Indiana University. All subjects wore single-vision spectacle lenses. RESULTS: The mean summer rate for the 42 subjects was -0.39 diopters per year (D/yr) (SD = 0.46). The mean school rate was -0.72 D/yr (SD = 0.57). The rates during the two periods were significantly different by two-tailed paired t-test (p = 0.006). CONCLUSIONS: The differing amount of nearpoint activity during the school year and the summer is a potential explanation for the different rates of myopia progression during those two time periods.

Child↗
PubMed1997

Microlamellar keratectomy for correction of high myopia.

OBJECTIVE: To evaluate the preliminary results of high myopia correction by microlamellar keratectomy (MLK). METHODS: Seventy-three eyes of 43 patients with high myopia were treated by MLK. The preoperative refraction ranged from -7.00D to -32.00D (mean -18.45D +/- 6.18D). All the operations were performed with the special apparatus for MLK. RESULTS: At 6 months after surgery, in the 73 eyes except 2 with new other symptoms, all the uncorrected visual acuity and corrected visual acuity were better than or equal to their preoperative ones respectively. Uncorrected visual acuity was better than or equal to the preoperative corrected visual acuity in 51 eyes (71.83%). No severe complications occurred during and after operation. The postoperative refractive status was stable. CONCLUSIONS: MLK is effective to reduce high myopia and has some special advantages as compared with radial keratotomy (RK), photorefractive keratectomy (PRK) and laser in-situ keratomileusis (LASIK). But influenced by several factors, the predictability of this procedure is merely fair. It is suggested that this kind of procedure must be done with excellent microsurgery equipments, microsurgical skills and much more clinical experience of managing corneal disorders.

Adolescent↗
PubMed1998

The organophosphate pesticide chlorpyrifos affects form deprivation myopia.

PURPOSE: The effects of the anti-cholinesterase organophosphate pesticide chlorpyrifos (CPF) on the refractive development of the eye were examined. Form deprivation was used to induce eye growth to address the previously reported relationship between organophosphate pesticide use and the incidence of myopia. METHODS: Chickens, a well-established animal model for experimental myopia and organophosphate neurotoxicity, were dosed with chlorpyrifos (3 mg/kg per day, orally, from day 2 to day 9 after hatching) or corn oil vehicle (VEH) with or without monocular form deprivation (MFD) over the same period. The set of dependent measures included the refractive state of each eye measured using retinoscopy, axial dimensions determined with A-scan ultrasound, and intraocular pressure. RESULTS: Dosing with CPF yielded an inhibition of 35% butyrylcholinesterase in plasma and 45% acetylcholinesterase in brain. MFD resulted in a significant degree of myopia in form-deprived eyes resulting from significant lengthening of the vitreal chamber of the eye. CPF significantly reduced the effect of MFD, resulting in less myopic eyes (mean refraction: VEH-MFD = -16.2 +/- 2.3 diopters; CPF-MFD = -11.1 +/- 1.8 diopters) with significantly shorter vitreal chambers. Nonoccluded eyes were, on average, slightly hyperopic. Treatment with CPF for 1 week in the absence of MFD led to no significant change in ocular dimensions or refraction relative to controls. CONCLUSIONS: The use of form deprivation as a challenge suggests that CPF treatment interferes with the visual regulation of eye growth.

Animals↗
PubMed1996

Refractive changes in chicks with form-deprivation myopia.

PURPOSE: To study the refractive changes of form deprivation of myopia. METHODS: Haisaik chickens were used to establish the animal models of myopia. Monocular eyelids were sutured for form deprivation on the 5th day after chickens birth. The chickens were examined by optometer and the anteroposterior axis, transverse and vertical diameters were measured by verniermicrometer. RESULTS: Form deprivation leads to myopic refractive abnormality (P < 0.001). The ocular anteroposterior axis (P < 0.005), transverse and vertical diameters lengthen (P < 0.05). CONCLUSION: Form deprivation is the main cause of the development of myopia.

Animals↗
PubMed1976

[Can myopia be influenced by the wearing of contact lenses?].

During 15 years the author has had the occasion to examine 11,454 spectacle wearing patients and 6,794 contact lens-wearing patients. In the age-group 15 to 25 years the contact lens-wearing patients manifested in 60% of the cases stationary myopia, whereas the spectacle-wearing patients in the same period manifested an increase of myopia in 75% of the cases. For a comparison in each patients visual acuity with and later without contact lens was determined, refraction performed and a slit lamp examination realized with and without contact lens. Determination of axial length of the eyes with the aid of ultrasonography could not be performed. The result of this analysis is compared with the results of other authors who have delt with the same problem. The author tries to give an explanation for the distinctly reduced increase of myopia in patients with contact lenses compared with those wearing glasses.

Adolescent↗