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The methods of performing keratomileusis and keratophakia are described. The principles of the calculations are outlined. Results and complications are enumerated. The indications for the methods are discussed.
A controlled outcome study on the effects of behavioral training on several measures of visual performance was conducted. Twenty-nine myopic subjects received complete optometric evaluations before being randomly assigned to one of three experimental groups. One treatment group received a behavioral training program with a feedback and reward component, another group received behavioral training without feedback and reward, and the third group was the no-treatment control group. In addition to measuring the effects of training on visual acuity and refraction, independent measures of axial length and intraocular pressure (IOP) were obtained for all subjects before and after treatment. An analysis of covariance indicated that axial length plays a significant role in mediating the effects of training.
AIM: To determine the association of spherical equivalent (SE) with low uncorrected visual acuity (VA) along with a proposed definition for myopia using logMAR VA >0.3 as the criteria. METHODS: 1334 Chinese schoolchildren (mean age 7.8; range 7-9 years) were enrolled in the study after those who had hyperopia > or =+2.00 dioptres (D) and astigmatism > = -2.00 D were excluded. Uncorrected logMAR VA was measured for both eyes. Cycloplegia autorefraction was achieved by the instillation of three drops of 1% cyclopentolate 5 minutes apart. The average of five successful consecutive refraction and keratometry readings were obtained with calibrated Canon RK5 autokeratorefractometers by well trained optometry students, at least 30 minutes after the instillation of the third drop of cyclopentolate. SE cut-off points (-0.25 D, -0.5D, -0.75 D, -1.0 D) were evaluated. RESULTS: Using different SE cut-off points, the myopia prevalence rates of this sample of schoolchildren varied from 45.8% (SE at least -0.25 D) to 30.7% (SE at least -1.0 D). The cut-off point of > or =-0.75 D had a sensitivity and specificity of 91.8% (95% CI, 89.2 to 94.4) and 93.7% (95% CI, 92.1 to 95.3), respectively, to predict low vision defined as uncorrected logMAR VA > 0.3 (either eye). The next best cut-off point of -0.5D had a higher sensitivity (93.3%), but lower specificity (87.9%). CONCLUSIONS: The cut-off points of -0.75D and -0.5D in SE refraction are appropriate for the prediction of uncorrected logMAR VA worse than 0.3, which is the criterion for the US common state adult driver licensing standard.
PURPOSE: To evaluate the effect of a two-stage laser in situ keratomileusis (LASIK) procedure on eyes with high astigmatism and/or anisometropia after penetrating keratoplasty. METHODS: Eleven postoperative penetrating keratoplasty eyes were included in a prospective, non-controlled study. All patients had at least 4.00 D of astigmatism and/or at least 3.00 D of anisometropia and were spectacle and contact lens intolerant. Two-stage LASIK was performed; in the first stage a hinged corneal flap 160 microm in thickness and 9 mm in diameter was created. After stabilization of corneal shape (1 to 3 months after keratotomy), the corneal flap was lifted and laser refractive treatment (second stage) was performed. RESULTS: After the first stage, a statistically significant reduction in refractive astigmatism (P<.01) was recorded. In all eyes but one, best spectacle-corrected visual acuity was maintained or improved after the procedure. Three months after the second stage, refractive astigmatism in 8 of 11 eyes (73%) was within +/- 1.00 D, and spherical equivalent refraction in 9 of 11 eyes (82%) was within +/- 1.00 D of intended correction. Preoperative irregular astigmatism persisted in three patients (3 eyes) who could not be corrected within +/- 1.00 D of refractive astigmatism and/or +/- 1.00 D of intended spherical equivalent refraction. In one eye, an interface infiltrate developed shortly after creation of the flap, and resulted in limited melting. CONCLUSIONS: A two-stage LASIK procedure improved visual acuity and refraction in postoperative penetrating keratoplasty eyes with high astigmatism and/or anisometropia. Complications were uncommon but can lead to loss of vision.
Collamer (collagen-acryl copolymer) intraocular contact lenses were implanted in the posterior chamber (sulcus) in phakic eyes to correct severe myopic patients. In addition to being myopic, they had visual problems (diminishing, contact lens coating) or direct organic eye problems (keratitis, conjunctivitis, vessel ingrowth in cornea) wearing glasses or standard contact lenses in everyday life. Seven lenses were implanted in four patients with preoperative myopia (spherical equivalents) ranging from -8.75 to -20.5 diopters (D), average myopia was -15.4, average follow up was 13.2 months. Mean postop myopia (spherical equivalent) was -1.96. Best spectacle-corrected visual acuity improved in all eyes with approximately two lines in Snellen's chart. No iritis or cataract was observed; one anterior angel closure required an additional iridotomia in one eye. The lens was well accepted, and a good functional outcome occurred within a short delay. The method holds promise as an important supplementary treatment for patients with severe refraction anomalies. It is, in fact, the only treatment for the most severe myopic and hypermetropic patients if they are to preserve their accommodative abilities.
Longitudinal records of 559 myopes were obtained from five optometric practices. A linear regression model was used to describe various parameters of myopia progression, including onset age, rates, and cessation age of childhood progression. Typical rates of childhood myopia increases are around 0.4 D/yr, although there is considerable individual variability. An earlier onset is correlated with the development of a higher final amount of myopia. The earlier cessation age of childhood myopia progression in females than in males is hypothesized to be related to growth factors.
PURPOSE: Whereas many previous studies have identified the association between sustained near work and myopia, few have assessed the influence of concomitant levels of cognitive effort. This study investigates the effect of cognitive effort on near-work induced transient myopia (NITM). METHODS: Subjects comprised of six early onset myopes (EOM; mean age 23.7 yrs; mean onset 10.8 yrs), six late-onset myopes (LOM; mean age 23.2 yrs; mean onset 20.0 yrs) and six emmetropes (EMM; mean age 23.8 yrs). Dynamic, monocular, ocular accommodation was measured with the Shin-Nippon SRW-5000 autorefractor. Subjects engaged passively or actively in a 5 minute arithmetic sum checking task presented monocularly on an LCD monitor via a Badal optical system. In all conditions the task was initially located at near (4.50 D) and immediately following the task instantaneously changed to far (0.00 D) for a further 5 minutes. The combinations of active (A) and passive (P) cognition were randomly allocated as P:P; A:P; A:A; P:A. RESULTS: For the initial near task, LOMs were shown to have a significantly less accurate accommodative response than either EOMs or EMMs (p < 0.001). For the far task, post hoc analyses for refraction identified EOMs as demonstrating significant NITM compared to LOMs (p < 0.05), who in turn showed greater NITM than EMMs (p < 0.001). The data show that for EOMs the level of cognitive activity operating during the near and far tasks determines the persistence of NITM; persistence being maximal when active cognition at near is followed by passive cognition at far. CONCLUSIONS: Compared with EMMs, EOMs and LOMs are particularly susceptible to NITM such that sustained near vision reduces subsequent accommodative accuracy for far vision. It is speculated that the marked NITM found in EOM may be a consequence of the crystalline lens thinning shown to be a developmental feature of EOM. Whereas the role of small amounts of retinal defocus in myopigenesis remains equivocal, the results show that account needs to be taken of cognitive demand in assessing phenomena such as NITM.
Chickens were raised with either translucent occluders or lenses, both under normal light cycles (12-h light/12-h dark) and in constant light (CL). Under normal light cycles, eyes with occluders became very myopic, and eyes with lenses became either relatively hyperopic (positive lenses) or myopic (negative lenses). After the treatment, retinal dopamine (DA), DOPAC, and serotonin levels were measured by high-pressure liquid chromatography (HPLC-EC). A significant drop in daytime retinal DOPAC (-20%) was observed after 1 week of deprivation, and in both DOPAC (-40%) and DA (-30%) after 2 weeks of deprivation. No changes in retinal serotonin levels were found. Retinal DA or DOPAC content remained unchanged after 2 or 4 days of lens wearing even though the lenses had already exerted their maximal effect on axial eye growth. When the chickens were raised in CL, development of deprivation myopia was reduced (8 days CL) or entirely blocked (13 days CL). Lens-induced changes in eye growth were not different after either 6 or 11 days in CL, compared to animals raised in a normal light cycle. Thirteen days of CL resulted in a dramatic reduction of DA and DOPAC levels, but serotonin levels were also lowered. The results suggest that lens-induced changes in refraction may not be dependent on dopaminergic pathways whereas deprivation myopia requires normal diurnal DA rhythms to develop.
The influence of defocus, artificial media opacities and pupil size on perimetric thresholds in automated light sense and flicker perimetry was investigated in 20 eyes of 20 normal subjects. Thresholds were determined at 13 locations in the central visual field. Blurring the retinal image by a small defocus or by slight artificial media opacities causes a measurable reduction in light-difference sensitivity. Flicker fusion frequency, however, is much more resistant to degradation of the retinal image. Artificial pupil size has a similar effect on both light-difference sensitivity and flicker fusion frequency. The present study shows that perimetric methods using temporal threshold criteria should be more suitable for the detection of neuronal damage in the presence of factors disturbing the quality of the retinal image than methods using static criteria.
Convex-shaped, hydrophilic lenticles of various water content were implanted into microkeratome-dissected corneal pockets in a baboon model. Freshly trephined, cryolathed, and factory-lathed hydrogels were evaluated for periods exceeding 15 months, documenting clinical response, corneal curvature shifts, and morphologic features. Previously implanted hydrogels were subsequently removed, documenting the reversibility of the procedure while allowing the corneas to return to their preoperative condition. Various alloplastic materials were then reimplanted into the same intrastromal pockets. Medium and high water content lenses produced good results without affecting the recipient cornea, whereas thick or low water content materials extruded or produced severe anterior segment inflammation. The use of medium and high water content, convex-shaped lenticles for the correction of aphakia is possible using current techniques.
The degree of aniseikonia with the correction of unilateral aphakia is mathematically and clinically much greater with glasses than with contact lenses. It is not possible to estimate the resulting aniseikonia on an individual basis from calculating the right-to-left difference between the retinal image sizes. However, both calculation of the differences between the retinal image sizes and the aniseikonia point out the advantage of contact lenses. Unilateral axial myopia (more than 90% of anisomyopias are axial) shows the smallest differences between retinal image sizes for glasses; however, measuring the aniseikonia with the phase difference haploscope shows the smallest amount of aniseikonia for contact lenses. This apparent contradiction can be explained by the "expansion" of the "granularity of perception" of the more myopic eye. Because the amount of "expansion" varies widely between individuals and is not known in particular cases, aniseikonia cannot be calculated but must be measured. Aniseikonia proved to be one of the most important factors in the development of amblyopia of the more myopic eye. Contact lenses are the best means of reducing the amount of aniseikonia in patients suffering from axial anisomyopia. In cases with minor anisomyopia it may be also possible to obtain a minor degree of aniseikonia with glasses. Exceptions such as "useful" and "malignant" anisomyopia must be taken into consideration.
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A new form of ectodermal dysplasia was observed in two siblings, offspring of healthy non-consanguineous parents. The main findings in both children are: hypodontia, abnormally shaped teeth, scalp hypotrichosis, pili annulati, follicular hyperkeratosis on the trunk and limbs, intensified delineation and reticular hyperpigmentation of the nape, and hyperopia; one of the siblings also has astigmatism. As both patients have normal nails and are euhidrotic, this is an ectodermal dysplasia of the pilodental subgroup. The cause is probably genetic and autosomal-recessive inheritance is most likely.
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Despite advances in microsurgical techniques, astigmatism after penetrating keratoplasty is still a perplexing problem. In this paper, using retrospective studies, experiments, and observations, the factors that seem most significant in creating excessive postoperative astigmatism are delineated. The difficulty of creating a circular recipient hole of the same size and shape as the donor button appears to be a prime area for clinical research and technical development.