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PubMed1995

Optical compensation for night myopia based on dark focus and CA/C ratio.

PURPOSE: To determine whether individual differences in dark focus and convergence accommodation to convergence (CA/C) ratio can be used to prescribe the best optical correction for night myopia. METHODS: The best correction for night myopia was obtained by measuring visual acuity and contrast sensitivity across a range of lens powers and luminances. Dark focus was measured with an infrared optometer, and CA/C ratio was measured with an infrared optometer and eyetracker. Only young subjects were used (mean age = 25.4 years). RESULTS: Optimal lens power was significantly correlated with dark focus, regardless of CA/C ratio. However, the slope of the regression line relating lens power to dark focus was steeper for subjects with CA/C ratios less than 0.4 diopters/meter angle (D/MA, n = 7) than for subjects with CA/C ratios greater than 0.4 D/MA (n = 9). The mean CA/C ratio for the entire sample (n = 16) was 0.59 D/MA. The mean optimal lens power and dark focus were -0.79 and 0.74 D, respectively, for the low CA/C group, and -0.60 and 0.91 D, respectively, for the high CA/C group. CONCLUSIONS: Visual performance in night myopia can be optimized by taking into account intersubject differences in dark focus and CA/C ratio. Best visual performance was found with a lens roughly equaling the full dark focus for subjects with low CA/C ratios and half the dark focus for subjects with high CA/C ratios.

Accommodation, Ocular↗
PubMed1995

[An intraocular lens power calculation for high myopia].

The accuracy of intraocular lens power calculation formulas for the axial high myopia were examined, especially regarding the point of the predictive refraction. We examined 170 eyes with axial lengths of 27 mm or longer, with postoperative visual acuity of 0.5 or more, and postoperative astigmatism of less than +/- 2D. Five formulas were tested for accuracy in predicting postoperative refraction. They were the L-SRK, SRK, SRK II, SRK/T, and Binkhorst formulas. The SRK formula tended to predict less myopia than the actual postoperative refraction. The SRK II and Binkhorst formulas predicted more myopia than the actual postoperative refraction. The best results were produced by the L-SRK and SRK/T formulas. The accuracy of the L-SRK formula predictions were measured for each of the four myopic levels. The same was done for the SRK/T formula. For both formulas, there was no statistically significant difference in accuracy of prediction for the four myopic categories. The two formulas are considered to be useful for high myopic cases.

Humans↗
PubMed1995

Expression of bFGF and TGF-beta 2 in experimental myopia in chicks.

PURPOSE: To determine factors that control ocular enlargement in experimental form-deprivation myopia and to clarify the mechanism of form-deprivation myopia. METHODS: After the left eyes of 20 chicks were monocularly occluded for 2 weeks, protein, basic fibroblast growth factor (bFGF) and transforming growth factor (TGF)-beta 2 contents in samples of constant area (circular button, diameter = 8.5 mm) in the retina-retinal pigment epithelium (RPE)-choroid and the sclera in the posterior region of control and myopic eyes were determined by enzyme-linked immunosorbent assay. RESULTS: The bFGF content (per circular button) and bFGF concentration (per mg protein) were significantly lower in the sclera in the posterior region of the myopic eyes than in control eyes. The bFGF content and concentration were similar in the retina-RPE-choroid in myopic and control eyes. The TGF-beta 2 content and concentration were significantly higher in myopic eyes in both the retina-RPE-choroid and the sclera (P < 0.05). CONCLUSIONS: These results are consistent with the possibility that bFGF and TGF-beta 2 regulate ocular enlargement or respond to myopiagenic mechanisms in form-deprivation myopia.

Animals↗
PubMed1995

[Asymmetric radial keratotomy for low-grade myopia].

Thirty patients (47 eyes) underwent a radial keratotomy for low myopia (from -0.75 to -2.5 D). Surgical technique was as follows: optical zone between 3.0 and 4.5 mm according to the degree of the myopia; two radial incisions in vertical superior and nasal horizontal meridian. The incisions were full thickness, obtained either with the "Russian" (centripetal) technique or with a centrifugal technique, but using a special designed knife. Mean refractive result was 1.73 D. For low myopia, our technique seems less traumatic and the refractive effect more rapidly steady.

Adolescent↗
PubMed1994

[Mechanism of axial elongation and chorioretinal atrophy in high myopia].

Myopic chorioretinal atrophy with axial elongation is one of the main factors of visual impairment in high myopia. To clarify the causes of this chorioretinal atrophy (CRA), the mechanism of ocular axial elongation was investigated from the effects of growth factors on experimental myopia models. From the analysis of large numbers of humans with extreme myopia, the factors causing CRA and the process of progression of this atrophy were also studied. I. Mechanism of ocular axial elongation Myopic change of 20 to 30 diopters occurred in chicks when they wore translucent or black opaque goggles for 2 weeks. But when they were fed under dark conditions for 24 hours, myopic change did not occur, and even when the goggles were worn, only slight myopic changes occurred. Thus, it appeared that light was necessary for myopic change and an increase in temperature caused by the goggles had little influence on the myopic change. In light microscopic observations, the posterior sclera of myopic chick eyes had thicker cartilaginous sclera and thinner fibrous sclera than the normal controls and abnormal proliferation of chondrocytes was seen at the border area. To investigate the changes in cell proliferation at 3 different locations (periphery, equator, posterior pole) of the sclera, the ratio of positive cells in PCNA, Decorin, b-FGF, TGF-alpha, TGF-beta, IGF-II, and phosphotyrosine were studied immunohistologically. Positive ratios were higher at the posterior pole of the treated myopic eyes for all factors, except for b-FGF and TGF-alpha. We estimated that the proliferation of chondrocytes and revelation of growth factors were higher at the posterior pole of the sclera in the experimental myopic eye than in the control eyes. In electron microscopic observations, proliferation of chondrocytes in cartilaginous sclera was found and small diameter collagen fibrils with a large amount of ground substance were observed in the fibrous sclera. These observations were similar to those of the sclera before hatching. It appeared that the sclera of the experimental myopic eyes remained in the pre-hatching condition. In co-culture experiments of the cultured condrocytes of cartilaginous sclera and the retina (retinal pigment epithelium (RPE) excluded), proliferation of the chondrocytes was suppressed significantly (p < 0.05). On the other hand, in the co-culture of chondrocytes and RPE-choroid, increase of the chondrocytes was induced (p < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

[Risk of retinal detachment in pseudophakia and axial myopia].

The incidence of retinal detachment on axial myopic pseudophakic eyes after Nd:Yag laser capsulotomy or intraoperative complications varies in the literature. In this study we analysed the incidence of retinal detachment in 136 pseudophakic myopic eyes (axial length > or = 26.0 mm) with and without capsulotomy and after intraopertive complications. These results were compared with those published in the literature and those obtained in a control group of 136 pseudophakic eyes with an axial length of less than 26.0 mm. Both groups were followed up for 2 years following operations in 1989 and 1990. The incidence of retinal detachment in eyes with axial myopia > or = 26.0 mm was 3.6% (5/136), without capsulotomy 3.3% (3/90) and with capsulotomy 2.5% (1/40). Intraoperative defects of the posterior capsule occurred in 6 cases, and in 1 case retinal detachment (1/6) developed. No retinal detachment occurred in the control group. The risk of retinal detachment does not seem to be significantly higher after uncomplicated extracapsular cataract extraction in eyes with axial myopia than in myopic eyes in which cataract extraction has not been performed. The combination of capsulotomy and axial myopia does not seem to increase the risk of retinal detachment. However, intraoperative complications do increase the risk of retinal detachment. Retinal detachment is three times as likely to develop in pseudophakic myopic eyes as in eyes with normal axial length.

Adult↗
PubMed1994

Effect of spectacle correction on the progression of myopia in children--a literature review.

BACKGROUND: Methods used to attempt to control childhood myopia progression have included various types of spectacle correction. The most commonly studied technique has been the use of bifocal lenses. METHODS: The literature on the effects of bifocals, undercorrection, and part-time wear of spectacles on the rate of myopia progression in children was reviewed. RESULTS: The data available on undercorrection and part-time wear of spectacles is limited. There have been several studies on the effects of bifocals. Some studies reported no effect with bifocals, some studies reported reduced rates with bifocals, and some noted lower rates with bifocals may be associated with particular ocular or visual findings. CONCLUSIONS: Critical analysis of the literature suggests that when the nearpoint phoria is eso, greater rates of progression occur, and that some degree of myopia control may be established by shifting the phoria into the normal range by spectacle corrections such as bifocals.

Child↗
PubMed1993

[Optic correction of myopia].

Correction of myopia by optics is still the most widely used method of visual rehabilitation. It raises visual acuity to levels that permit a normal life in a world where vision is particularly important. This success of glasses and lenses is most perfect for mild or moderate myopia. For subjects with severe myopia glasses are not without problems and contact lenses are preferable, but the results sometimes remain mediocre due to organic disorders resulting from excessive lengthening of the eyeball.

Adolescent↗
PubMedDate not supplied

[The treatment of myopia by photoreactive keratectomy (PRK) with the 193-nm excimer laser].

Excimer laser photokeratectomy is the most recent procedure used for correcting myopia surgically. It consist in flattening the cornea by performing ablations of a part of its anterior stroma. Over 15,000 patients underwent this almost entirely robotic surgical intervention, supposed not to present the shortcomings of radial keratotomy. This robotic surgery tend to replace radial keratotomy. Photokeratectomy is designed to correct all kinds of myopia, astigmatism as well as these resulting from such surgical interventions as cataract extraction or Keratoplasty. A bifocal photorefractive keratectomy is expected to correct the myopia of the patients who reached the age of presbyopia.

Animals↗
PubMedDate not supplied

Cryolathe keratomileusis for correction of myopia of 4.00 to 8.00 diopters.

BACKGROUND: During the last decade, new refractive surgery procedures have been introduced; older techniques have been modified or even abandoned. Cryolathe myopic keratomileusis has been in clinical use for approximately 30 years. In this retrospective study, we present our experience in applying this technique for the correction of 4.00 to 8.00 diopters of myopia. METHODS: Autoplastic cryolathe keratomileusis was performed on 61 eyes of 44 patients who were at least 18 years of age, with a preoperative myopia of 8.00 D or less, and 4.00 D or less of astigmatism. The surgical technique used the Barraquer microkeratome and cryolathe. The mean postoperative observation period was 28 months (range, 12 to 73 months). RESULTS: The mean preoperative spherical equivalent refraction was -5.95 +/- 1.14 D (range, -4.25 to -8.00 D). After a mean follow up of 28 months, the mean postoperative spherical equivalent refraction was -0.91 +/- 1.49 D (range, +2.00 to -7.75 D). At the end of follow up, 37 eyes (60.7%) were within +/- 1.00 D of emmetropia and 44 eyes (72.1%) achieved 20/40 or better uncorrected visual acuity. Complications included corneal ectasia in one eye (1.6%) and epithelial inclusions of the interface in another eye (1.6%). Irregular astigmatism was not a major problem, occurring in only two eyes (3.3%). CONCLUSIONS: Cryolathe keratomileusis is a proven and feasible technique for correcting moderate to high amounts of myopia in properly selected patients; there is a low incidence of vision-threatening complications.

Adolescent↗
PubMedDate not supplied

The erodible mask in photorefractive keratectomy for myopia and astigmatism.

This paper reports a new approach for performing photorefractive keratectomy (PRK) that uses an erodible mask to control shape transfer processes. The advantages of this technique, when compared to conventional PRK performed with mechanical diaphragm, are 1) the possibility of transferring almost any shape onto corneal surface; 2) a smoother corneal surface following photoablation; 3) easier eye fixation; and 4) a controlled humidified environment over ablation zone. We report our experimental study on scanning electron microscopy of polymethylmethacrylate (PMMA) plates ablated using conventional technique versus erodible mask technique; the results showed a smoother surface in the PMMA plate ablated using the erodible mask. We also report our preliminary clinical results of four eyes treated for the correction of myopia combined with astigmatism. Myopia ranged from -2.00 to -10.00 D, and astigmatism ranged from -1.50 to -2.50 D. Three months after surgery, all four eyes were within +/- 1.00 D of myopic attempted correction, but astigmatism was completely corrected only in one eye. No complications or scarring have been reported. We believe the erodible mask could be effective in the correction of myopia and myopic astigmatism, but further improvements are necessary to allow easier alignment of the mask over the eye. All commonly available excimer laser devices produce photorefractive keratectomy as a concentric ablation of the corneal stroma, deeper in the center than in the peripheral part; this is produced by means of an iris or diaphragm which, depending on the type of laser, progressively opens or closes, allowing a greater laser beam delivery in the center.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Photorefractive keratectomy for myopia from 6.00 D to 10.00 D.

Surgical correction of mild and high myopia using excimer laser photorefractive keratectomy (PRK) remains controversial. We present a retrospective study of 40 consecutive PRK procedures performed to reduce myopia ranging from -6.00 D to -10.00 D. Postoperative follow up was 24 months. The mean preoperative spheroequivalent refraction was -8.12 +/- 1.52 D; postoperatively it was -2.31 +/- 1.25 D. In 26 of 40 eyes (65%) we observed a regression of the refraction effect after 6 months. In 85% of eyes a persistent corneal haze (+1 grading) was observed at the end of follow up. Photorefractive keratectomy to correct or reduce mild or high myopia is simple and safe but had poor predictability and significant refractive regression in this series.

Adolescent↗
PubMed1996

[Extraction of a clear lens-cataract as refractive surgery in severe myopia].

Fukals operation (extraction of a transparent lens in severe myopia) was of a long time considered risky in particular because of possible retinal complications. Based on ten years experience (1985 - 1994) the authors provide evidence that modern microsurgical methods, in particular phacoemulsification make it possible to perform this operation at a qualitatively higher level, much more safety and with a lower rate of complications. In a group of 284 operated eyes with myopia (15.96 diopters) were 4.57% transparent lenses, 37.68% with mild partial turbidity and 57.75% with dense or complete turbidity. Corrected vision 5/5 - 5/10 was achieved in 44.37%. Peroperative prolapse of the vitreous body occurred in 5.28%. The most frequent late complication was secondary cataract (26.76%). During the mean follow-up period of 37.57 months there was no case of cystoid oedema of the macula or detachment of the retina. Extraction of a transparent lens or incipient cataract in severe myopia is becoming an alternative method of other refractive operations.

Adolescent↗
PubMed1996

Evaluation of three different approaches to perform excimer laser photorefractive keratectomy for myopia.

BACKGROUND AND OBJECTIVE: The aim of this study was to evaluate the results of myopic excimer laser photorefractive keratectomy (PRK) performed using three different ablation approaches. PATIENTS AND METHODS: Using the Apex excimer laser (Summit Technology, Inc., Waltham MA), we have treated 75 eyes. Twenty-five of them were treated by a single ablation zone (SA, 6.5 mm diameter) to correct myopia of -4.50 +/- 2.10 D (mean +/- SD); 25 eyes underwent PRK for the correction of myopia of -4.98 +/- 2.17 D using a multipass multizone technique (MP, 3 zones); and 25 eyes were corrected for myopia of -5.03 +/- 1.98 D using new software which enables the creation of three ablation zones in a single-pass fashion (MZ). RESULTS: Mean refractive error (+/-SD) at the first post-operative month was +1.34 +/- 1.00 D for SA, +1.78 +/- 1.49 D for MP, and +0.90 +/- 0.75 D for MZ. Eyes treated by MZ had significantly better uncorrected visual acuity than those treated by SA (P=0.04). Corneal topography revealed a central island in 14 eyes (56%) of those treated by SA and 2 eyes (8%) of those treated by MZ, but in no eyes treated by MP. Six months after treatment, mean refractive error was +0.28 +/- 0.75 D for SA, +0.36 +/- 0.92 D for MP, and - 0.07 +/- 0.77 D for MZ. CONCLUSION: MZ ablation induced less hyperopic shift at 1 month, thus leading to a faster visual recovery and better uncorrected visual acuity. MP and MZ ablations proved effective in preventing central island formation, thus inducing less visual disturbances than SA ablations. These results suggest that MZ ablation may be preferable to the other techniques in performing myopic PRK.

Adult↗
PubMed1996

Multizone versus monozone in the treatment of high and moderate myopia with an excimer laser.

BACKGROUND AND OBJECTIVE: Numerous modifications have been proposed to photorefractive keratectomy (PRK) in the treatment of myopia in excess of 6.00 diopters (D). One of the techniques employed in an attempt to achieve better refractive results and to avoid, above all, the appearance of an intense haze, is the technique known as multizone. PATIENTS AND METHODS: We have attempted, in a prospective study, to compare the refractive results and the complications of monozone and multizone techniques for the treatment of moderate and high myopia. We performed 139 monozone PRKs and 30 multizone PRKs with a one-year follow-up. RESULTS: We did not find statistically significant differences between the two groups either in the degree of correction obtained nor in the final visual acuity. A statistically significant difference was found only in the number of cases with severe haze (greater than 3) which proved more frequent in the monozone group. CONCLUSION: Our results suggest the techniques are comparable in predictability and effectiveness. However, the incidence of severe haze was lower in the multizone group, which may render its use preferable in the treatment of myopias in excess of 6.00 D.

Corneal Opacity↗
PubMed1995

Tapered transition zone and surface smoothing ameliorate the results of excimer-laser photorefractive keratectomy for myopia.

This report compares the results we obtained after photorefractive keratectomy (PRK) for myopia using different treatment modalities. PRK was performed on 35 eyes (group 2; mean refraction, -5.7 +/- 2.3 D) using a tapered transition zone (TTZ), smoothing of the corneal surface, and somewhat more steroids than usual. The results were compared with those obtained in another group of patients (group 1) with equally high myopia in whom these measures were not used. Quicker rehabilitation and stabilization of visual acuity (VA) and less regression were observed. An uncorrected VA of +/- 20/40 after 9 months was found in 94.4% of eyes in group 1 (P = 0.026). A refraction of +/- D after 9 months was found in 89% of eyes in group 2 and in only 58% of eyes in group 1 (P = 0.024). Haze reduction was quicker and stronger in group 2, and fewer patients in this group suffered loss of best corrected VA. The results of PRK of myopia can be ameliorated thanks to improved technique and increased experience.

Adult↗
PubMed1996

A preliminary clinical report of automated lamellar keratoplasty with excimer laser keratectomy for correction of high myopia.

OBJECTIVE: To evaluate the therapeutic effects of automated lamellar keratoplasty combined with excimer laser keratectomy (ALK-E) for the correction of high myopia. METHODS: With the automated corneal shaper and Keracor 116 excimer laser, ALK-E was performed on 47 eyes of 40 cases with myopia of -8.00 to -30.00 diopters (mean, -14.55D +/- 5.14D) and the highest astigmatism 7.00D. Postoperatively, all patients have been followed up for at least 3 months. RESULTS: The refractive status and visual acuity tend to be stable about 1 month postoperatively. For myopes below -15.00D, the mean refraction was -1.33D +/- 1.05D at 3 months, and 66.7% achieved their preoperative best corrected visual acuity. For myopes over -15.00D, the mean refraction was -2.42D +/- 1.84D at 3 months and 52.9% achieved their preoperative best corrected visual acuity. CONCLUSIONS: The early therapeutic results of ALK-E for treatment of high myopia are very promising. However, the operative techniques, parameters and remote therapeutic results remain to be further studied.

Adolescent↗
PubMed1996

[A clinical investigation on scleral reinforcement for treatment of high myopia].

OBJECTIVE: The study was designed to observe the therapeutic effects of scleral reinforcement in treatment of high myopia. METHOD: 86 patients (109 eyes) with high myopia were treated by scleral reinforcement using silicone sponge and heterogeneous sclera. RESULTS: Postoperatively, the naked visual acuity increased in 71.9% of all the eyes in 1-4 years of follow-up. 69.9% of them had a stable axial length, and the volume of blood flow in ophthalmic artery increased in some eyes. CONCLUSION: Scleral reinforcement has therapeutic effects in treatment of high myopia. The surgical techniques applied were mentioned.

Adolescent↗