ABSTRACT In the period of almost 100 years since Javal proposed an empirically determined rule for the prediction of refractive astigmatism on the basis of corneal astigmatism, many authors have made suggestions for the modification of “Javal's Rule.” These modifications, rather than being based on clinical data, have been based on concepts of mechanisms that can contribute to refractive astigmatism, but in most cases the modifications do nothing more than complicate the process of predicting refractive astigmatism, with the result that only Javal's original rule is widely used. In this paper, keratometric and refractive data for three groups of subjects are used to demonstrate that a simplified version of Javal's rule is more effective in predicting refractive astigmatism than is Javal's rule itself.
ABSTRACT Tait described four categories of binocular disorders including convergence excess, convergence insufficiency, divergence excess, and divergence in sufficiency. These disorders are defined by the distance where the largest heterophoria occurs (distance or near), and the amplitude of the accommodative vergence ratio (AC/A). Insufficiency corresponds to a low AC/A ratio, whereas excess corresponds to a high AC/A. The magnitude of the AC/A ratio, which may be influenced by the adaptability of the accommodaation and vergence systems, has been shown to be reciprocally related to adaptability of accommodation. Likewise, the degree of vergence accommodation has been shown to be related reciprocally to adaptability of vergence to prism. An imbalance of adaptability of accommodation and vergence systems produces abnormal cross‐coupling between the two motor systems. When accommodation is more adaptable than vergence, the AC/A ratio is low and the CA/C ratio is high. Conversely, when vergence is more adaptable than accommodation, the AC/A ratio is high and the CA/C ratio is low. A method is reported for temporarily restoring moderate amplitudes of abnormal AC/A and CA/C ratios by reducing excessive adaptation with fatigue. Finally, new clinical procedures for measuring adaptation of accommodation and the CA/C ratio are presented. Taken together with current measures of vergence adaptation and AC/A ratio these procedures will permit a more complete evaluation of mutual interactions between accommodation and vergence in patients diagnosed as having excessive and insufficient vergence.
This paper is a review of the literature relative to treatment results for convergence insufficiency utilizing vision therapy training procedures. Vision therapy is shown to improve the nearpoint of convergence and fusional convergence and to ameliorate associated symptoms. The overall cure rate is 72%. Furthermore, the training results appear to persist for at least 2 years if the patients are initially cured and are independent of age until the late presbyopic years. Also, recent studies indicate the type of training procedures which yield the most effective training results.
An instrument using an electro-optical Fourier method for measuring the modulation transfer function (MTF) of low power telescopes and telemicroscopes is described. Because these devices are afocal, or nearly so, relay optics are needed to form real images at the detection section of the apparatus. The system is capable of measuring the MTF in monochromatic and white light, at any target azimuth, across the field of view, and through focus. The target system contains 14 square-wave gratings with spatial frequencies that range from 2.5 to 156 cpd. Images of these gratings are scanned across a slit. The output data are fed to a first-order recursive digital Butterworth bandpass filter for MTF analysis. The apparatus is diffraction limited at f/31.4. Therefore, it negligibly affects the measurement of the MTF of telescopes and telemicroscopes tested with exit pupils of up to 6.4 mm.
Until recently, convergence limits have been measured only in the primary position of gaze. A new instrument permits such measurements in all directions of gaze and at various angular distances from the primary straight-ahead position. Aberration and distortion-free stimuli based on Heine's principle were incorporated in the apparatus. For each of the nine subjects participating, convergence limits were obtained in the primary straight-ahead position, secondary, and tertiary positions and in varying degrees of obliquity of these directions of gaze. The convergence limits were measured in 10 degrees steps away from the straight-ahead position of gaze in 18 different meridians. It was found that convergence limits vary markedly with the direction of gaze, the maximal vergence range usually being found between 10 to 20 degrees below the primary horizontal plane in the lower right-half field, possibly because subjects spend most of their time looking in this direction.
Radial keratotomy (RK), a popular procedure for reducing myopia, does not always have a successful outcome. Of the adverse effects reported in the literature, there have been few reports of undesirable disturbances of binocular vision. Four representative cases are reviewed which presented clinically with varying binocular problems induced by RK. The treatment considerations and final solutions for each are discussed. In the presence of RK-induced anisometropia, aniseikonia can be a particularly debilitating binocular vision problem for some patients.
Conflicting reports on the adequacy of the visual performance provided by hydrogel contact lenses continue to appear in the literature. We conducted a study to determine the effect on visual performance, as assessed by contrast sensitivity measurements, of (1) lens wear of optimally fitting 38% water content lenses and (2) altered lens parameters, including fitting characteristics, of 38% and 67% water content lenses. During normal wear of lenses, neither the lenses themselves nor any contact lens-induced corneal changes produced measurable visual losses. The visual performance was also independent of lens fit or lens thickness over the ranges used here. The higher water content lenses provided marginally poorer visual performance.
Pre- and post-task measures of dark focus (DF) were used to assess the response of the accommodative system to within-task disparity-vergence in 10 late-onset myopes (LOM's) and 10 emmetropes. Disparity was induced by 3 and 6 delta base-out prisms imposed during a 3 D near-vision task undertaken for 3- and 10-min periods. Accommodation was measured after the task at 1-s intervals over a 90-s period using an objective infrared optometer to determine post-task regression of DF toward pretask values. After the 3-min task both groups show a reduction in DF adaptation with increasing disparity-vergence. After the 10-min task, disparity continues to have a significant effect on accommodative adaptation in LOM's but not in emmetropes, suggesting diminished prism adaptation in LOM's. The implications of these findings are discussed with regard to both current models of accommodation-vergence interaction and the etiology of late-onset myopia.
One of the advantages suggested for contact lens bifocals over monovision treatment of presbyopia is that there may be less impairment of binocular function. We evaluated nearpoint stereoposis on the Titmus stereotest for 10 presbyopic patients. Testing was done under five conditions; monovision and binocular correction with each of four marketed simultaneous bifocal contact lenses. Simultaneous vision bifocals tested produced at least as much reduction in stereopsis as monovision compared to baseline spectacle correction. Repeat testing of bifocal stereopsis with best near over-refraction suggested that a substantial portion of the stereo reduction could be attributed to insufficient effective adds with the bifocal contacts.
The purpose of the study was to determine to what extent induced aniseikonia affects fixation performance. Aniseikonia was induced in the vertical meridian only, whereas fixation alignment was monitored in the horizontal meridian. A previously developed technique based on the dependency of border enhancement bandwidth on fixation eccentricity was used to monitor deviations from central fixation during fusion. Stress on the fusion mechanism was supplied by controlled increments of forced horizontal vergence. It was found that deviation from central fixation in the horizontal meridian generally increases with increasing amounts of vertical aniseikonia. The effect is particularly pronounced for small amounts of aniseikonia.
Goldmann perimetry was done on 11 pseudophakic subjects and results were compared to those of age-matched phakic subjects and a third group of aphakic individuals who were wearing rigid gas permeable contact lenses. Testing showed that the I-3 and I-4 fields of the subjects who had had cataract surgery were generally constricted when compared to the normal phakic population. Possible explanations for this include media clarity not being as important a factor in determining field size as was previously thought, peripheral retinal changes, and implant material affecting contrast sensitivity.
A clinical trial was conducted to compare the extended wear performance of rigid gas-permeable (RGP) contact lenses with that of soft lenses. Subjects were fitted with a RGP lens (Boston IV) in one eye and a soft lens (Bausch & Lomb "O" series) in the other eye, and wore them on an extended wear basis for up to 3 months. No subjects developed any acute adverse reactions in the RGP lens-wearing eye. After the initial adaptation period, subject acceptance of RGP extended wear in terms of vision and comfort was superior. The RGP lenses also induced less chronic hypoxic stress than hydrogel lenses of comparable Dk/L, as evidenced by the presence of epithelial microcysts. Several complications of RGP extended wear were observed including lens binding, blepharoptosis, transient pupil size increases, and corneal staining. As hypoxia-induced corneal changes, such as microcysts and striae, were observed in the RGP lens-wearing eyes, we consider that these particular RGP lenses do not have adequate oxygen transmissibility for successful long-term extended wear. However, if RGP lens materials of higher oxygen transmissibility and better designs can be attained, the potential of RGP extended wear would appear promising.
Change in fixation disparity was measured as lens sphere power was changed at distance and near on a young adult population. The results were graphed to yield a lens-induced fixation disparity curve. The lens curves found were grouped into four basic types (A through D). Two types (A and B) had increasing eso fixation disparity with increasing minus lens power. Type C had little change in fixation disparity with any change in lens power, whereas type D had an initial increase and then no further change with increasing minus power. In addition, approximately 74% of the 38-subject sample had different curve types at distance and near. Possible clinical uses of the lens-induced fixation disparity curve include the prescribing of near additions for pre-presbyopes based on measures of the binocular vergence response to various lens sphere combinations.
Although accommodative facility testing is used widely in the evaluation of accommodation in children, published normative data are not available for this age group. Current values being used are based upon studies of adult populations. In order to establish norms, 542 elementary schoolchildren were screened. Those that passed a specific set of criteria were included in the accommodative facility assessment. We used a new target and instructional set, which took into consideration the problems associated with subjective testing of young children. The results revealed lower mean accommodative facility values for both monocular and binocular accommodative facility than the values obtained previously from adult populations. These new findings can be used as a clinical guide to evaluate accommodative facility in young children.
American Foundation for the Blind, Inc., New York, New York (From a speech delivered at the American Academy of Optometry's Annual Meeting, December 6, 1987, on the presentation to him of the Carel C. Koch Memorial Medal.) This speech was presented at the Annual Meeting of the American Academy of Optometry in Denver, Colorado, 1987. Received March 10, 1988. * M.S.W., Executive Director. AUTHOR'S ADDRESS: William F. Gallagher American Foundation for the Blind, Inc. 15 West 16th Street New York, New York 10011
Results of refractive component measurements have shown that eyes of Melanesian schoolchildren living in Vanuatu, almost all of whom are emmetropic, have relatively short axial lengths and relatively flat corneas in comparison to emmetropic eyes of children examined in England. Evidence is presented to suggest that the relation between the axial length of the eye and corneal radius--the axial length/corneal radius (AL/CR) ratio--may be a useful predictor of future refractive state. Mean axial length/corneal radius ratios for 6- to 19-year-old Melanesian school children were found to be 2.88 for boys and 2.86 for girls, as compared to mean AL/CR ratios for 6- to 19-year-old British schoolchildren of 3.05 for boys and 3.04 for girls. It is proposed that an eye having a high AL/CR ratio is at risk for the development of myopia, and that such an eye has maintained its state of emmetropia by virtue of a compensatory flattening of the crystalline lens. In order to test the proposition that an increase in axial length occurs as a precursor to the development of myopia, a prospective longitudinal study of a group of 6- to 7-year-old schoolchildren is proposed.
State University of New York State College of Optometry 100 East 24th Street New York, New York 10010-3677
This paper describes three sisters, triplets, age 7 years, 2 months, two of whom derive from a single ovum, the third from a second ovum. As such, they provide an opportunity to examine the relative impact of heredity on certain of their physical, developed, and acquired abilities and characteristics. In addition to a comparison of such physical traits as height, weight, refractive status, axial length, and so on, certain (developed) sensory-motor and (acquired) cognitive and language measures are reported, such as binocular status, visual and auditory analysis skills, intelligence quotient, and (expressive and receptive) language abilities. Because all three children have lived in (more or less) the same pre- and post-natal environment, we assume that whatever concordance the monozygotic (MZ) pair displays that is not shared by their dizygotic (DZ) sister is attributable to heredity. (It does not necessarily follow, however, that any discordance between the two MZ sisters or any concordance between one of them and their DZ sister is attributable to environment.
Imaging of human brain structure and activity with particular reference to visual function is reviewed along with methods of obtaining the data including computed tomographic (CT) scan, magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and positron emission tomography (PET). The literature is reviewed and the potential for a new understanding of brain visual function is discussed. PET is reviewed from basic physical principles to the most recent visual brain findings with oxygen-15. It is shown that there is a potential for submillimeter localization of visual functions with sequentially different visual stimuli designed for the temporal separation of the responses. Single photon emission computed tomography (SPECT), a less expensive substitute for PET, is also discussed. MRS is covered from basic physical principles to the current state of the art of in vivo biochemical analysis. Future possible clinical applications are discussed. Improved understanding of the functional neural organization of vision and brain will open a window to maps and circuits of human brain function.
Usually two factors are not rigidly standardized in the routine tangent screen examination: (1) the stimulus characteristics of the carrier that fixes the spot to the wand, and (2) patient instructions about what aspects of the stimulus they should attend to. Differences in these factors within the range of what is commonly done in the tangent screen test can lead to significant differences in the locations of the isopters. There is also an interesting interaction between these two factors in establishing isopter size.
