ABSTRACT The design of aniseikonic corrections is discussed and tables are presented which simplify the procedure consistent with laws requiring “impact‐resistant” lenses for all patients. Evaluated are effects on magnification of lens vertex distance, base curves, and thickness changes. The tables presented can also be used to evaluate and reduce inadvertent introduction of aniseikonia due to variation in lens thickness or curvature when a patient's lens(es) are replaced.
The Griffin flexible contract lens is described, and the methods for its use are discussed.
ABSTRACT The latency of the fusional vergence or the disparity vergence system has been found to vary from 130 to 250 milliseconds for unpredictable inputs. It has also been established that there is a prediction operator in the system which seems most effective around the 0.5 Hz region. The experiments also indicate a hitherto unnoticed difference between the convergence and the divergence latencies, with the latter being shorter. Similarities between the accommodation and the fusional vergence systems in terms of their latency and prediction characteristics are indicated by the results, but further work is necessary to test these correlations.
The dominant eye has been defined as the eye which is used to sight with, or whose input is favored when there is conflicting information to the two eyes. Many investigators report differences in measured dominance as a function of the test used. Fifty-seven normal subjects were tested on thirteen different tests for ocular dominance. Analysis of the results reveals three types of ocular dominance: sighting dominance, sensory dominance and acuity dominance.
The equipment for the procedure is listed followed by a step-by-step discussion of the methods used to determine the correction of the refractive error of the two eyes during the presence of fused binocular vision.
Surgical binoculars were modified for use in contact lens practice, and the advantages of the modification presented.
The mechanisms involved include retinal interaction, adaptation at the level of the bipolars in the retina and eye movements. Adaptation at the bipolar layer introduces a non-linear relation between the photoreceptor response and the ganglion cell response. It also sets an upper limit to the response of the bipolars and were it not for eye movements the visual field would be reduced to a uniform brightness at high luminance levels. The eye movements prevent a difference in adaptation on the two sides of a border and thus provide for a difference in the response on the two sides of a border. Lateral inhibition has a greater spread than excitation and thus also accentuates the brightness at borders. A special frequency equalizing mechanism is postulated to explain the perceived uniformity of a surface between two borders. Surface contrast and border contrast involve the same mechanisms.
Mueller-Lyer figures were presented tachistoscopically in illuminant C in four experiments which explored the effects of viewing time (500, 1500, 4500 and 9000 msec), contrast level (1.5 black/, 5 gray/, 7.5 light gray/ each on 9.5 white/ background) and fundus pigmentation on the magnitude of illusion. Significant interactions of contrast level and viewing time were evident. Results further indicate density of fundus pigmentation to be related significantly to illusion magnitude at the shortest viewing time, with more darkly pigmented Ss yielding a significantly smaller illusion than lightly pigmented Ss sampled from a white population. Illusion magnitude at a reduced viewing time would seem to be a function of absolute contrast.
After establishing the diurnal changes of cholesterol in the tears of a sample of patients, each was fitted with contact lenses. An abrupt, but temporary, decrease in tear cholesterol was observed in all until full wearing time was achieved. Post adaptation levels, however, were found not significantly different from pre-fitted levels. The relationship of tear cholesterol to the adaptation process and the possible contraindications excessive levels may have for wearing success are discussed.
A rose-colored lens called a DOC Lens is described as being useful to both aviators and snow skiers. The spectral transmission, luminous transmittance, and chromaticity of the lens are assessed.
ABSTRACT Groups of plano ophthalmic lenses 48 mm round and 2.2 mm thick were tested in a drop‐ball tower conforming to both F.D.A. regulations and ANSI standards. Lenses were impacted with steel balls of different sizes from different heights to provide a scale of increasing equal energy increments. One of the energy levels was provided by the standard 5/8‐inch ball dropped from a height or 50 inches. The fracture resistance (drop ball energy) of anncaled (untempered), heat tempered and chemically tempered lenses are compared graphically and statistically. The annealed group had the lowest mean fracture energy over the narrowest range. The chemically tempered group had the highest mean fracture energy over the widest range. Experiments attempting to predict which untempered lenscs would be most fracture resistant when tempered are described and interpreted in terms of modern glass strength theory.
ABSTRACT Binocular eye movement recordings and laser‐target retinal cinematography were employed to identify a fixation bias in a case of hereditary congenital nystagmus. The oscillations of each eye varied with gaze angle and were, in general, unequal over a ± 30° range of gaze. Although the nystagmus frequency was also gaze‐angle dependent, it was equal in both eyes. In the null region both nystagmus amplitude and frequency were minimal and equal for the two eyes. The lateral fixation bias was found to occasionally shift in direction simultaneously in both eyes: this preserved retinal correspondency and, in conjunction with the nulling effect of convergence and proper gaze angle, contributed to increased visual acuity. These findings support and further clarify the mechanisms by which the previously described prism lenses dramatically increased visual acuity. The attempt to fixate was identified as the adequate stimulus for the nystagmus.
ABSTRACT The purpose of the study was to establish for a large sample the validity of the laser refraction technique. Using the method spherical errors were determined for the dominant eyes of 100 observers. Their task was to observe through a phoropter a defocused laser pattern and report when the speckle movement ceased. The data were analyzed for four refractive groups (low myopes, high myopes, low hyperopes, high hyperopes) in terms of the degree to which the laser findings correlated with the other objective and subjective techniques for determining spherical error. It was found for all groups that the laser determinations were highly valid. The laser findings were also analyzed for each group to determine the variability of the procedure, and the results confirmed our earlier findings that the technique is also very reliable. Taken as a whole, the findings indicate that laser refraction may have greater application than mere use in gross screening situations, as is often asserted.
