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PubMed1984

Accommodative range in amblyopic monkeys (Macaca nemestrina).

Three naturally strabismic and two chronic bilaterally atropinized monkeys were tested for spatial contrast sensitivity and range of accommodation. All eyes that showed deficits in contrast sensitivity also showed deficits in accommodation. The strabismic monkeys all showed interocular differences in their CSFs and in their accommodative ranges. The atropine monkeys had no interocular differences on either measure. However, one had depressed contrast sensitivity relative to normal and also showed a reduced accommodative range. A statistically significant correlation was found between the high frequency cutoffs of the CSFs and accommodative ranges. These deficits in accommodative range that accompany contrast sensitivity losses in the monkey are similar to the deficits in accommodative range that accompany amblyopia in humans.

Accommodation, Ocular↗
PubMed1984

Penguin vision in air and water.

Refractive states measured by retinoscopy and photorefraction indicate that rockhopper (Eudyptes crestatus), Magellanic (Spheniscus magellanicus) and gentoo (Pygoscelis papua) penguins are approximately emmetropic in air and water. Extensive myopia in air, as predicted by early authors, is nonexistent. Photorefractive measurements of refractive state in water indicate that rockhopper, gentoo, Magellanic and king (Aptenodytes patagonica) penguins can accommodate sufficiently to make up for the loss of refractive power of the cornea. Corneas of rockhopper and Megellanic penguins are flattened relative to the overall size of the eye. This feature minimizes the optical effect of submergence.

Accommodation, Ocular↗
PubMed1984

The effect of contrast on sustained detection.

During a 1 min observation, the percentage of time a high spatial frequency grating can be detected is influenced by the contrast and spatial frequency of a second, superimposed and orthogonally-oriented sine wave grating. Increasing contrast of the second pattern aids detection of the first by providing a more effective accommodative stimulus. The function relating spatial frequency and the minimum contrast needed to activate accommodation is similar in shape to the classical contrast sensitivity function. However, an order of magnitude more contrast is required to stabilize accommodation than is required to simply detect a pattern. These results suggest that performance on visual tasks requiring sustained rather than brief detection may be markedly impaired under low contrast conditions.

Accommodation, Ocular↗
PubMed1984

Analysis of human crystalline lens curvature as a function of accommodative state and age.

Slit-lamp photographs from four human subjects, aged 11, 19, 29, and 45 were reanalyzed using computer-based digitization and curve-fitting methods in order to obtain more complete information on internal lens curvature changes during accommodation. All discernible curves (N = 742) could be fit to parabolas with chi 2 less than or equal to 0.001 irrespective of lens age, accommodative state, or curve location within the lens. For each lens, the coefficients of the parabolas, when displayed in graphic form, exhibit a linear relationship between location within the lens and the coefficient of the chi 2 term. The slope of this line remains unchanged over accommodation for a given lens, but is shifted in position. The slope changes as a function of age. The age 45 lens exhibits these characteristics to a limited extent only, the differences possibly related to the development of presbyopia. The further a given curve is located from the lens surface, the smaller the region of its arc that can be considered approximately circular. A roughly hourglass figure is generated by these circular bounds; the waist of the hourglass decreases with increasing accommodation, since changes in radius of curvature with accommodation are more pronounced internally. Calculations of arc lengths as a function of increasing accommodation indicate that these lengths change very little over the entire accommodative range.

Accommodation, Ocular↗
PubMed1984

Refractive state, depth of focus and accommodation of the eye of the California ground squirrel (Spermophilus beecheyi).

Retinoscopy and electrophysiological refraction were performed on 55 and 24 far-accommodated eyes of California ground squirrels (Spermophilus beecheyi), respectively. These two indices were highly correlated, revealing the eye of this animal to be roughly emmetropic (-0.25 to -0.13 D). Depth of focus was assessed by measuring the effect which defocusing produced on the spatial resolving power of 32 optic nerve fibers. Depth of focus of the ground squirrel eye for a pupil diameter of 2.5 mm is estimated to be +/- 1.6 D, but will increase rapidly for smaller pupils. Accommodation in eleven ground squirrels ranged from 2 to 6 D, with a mean value of 3.9 D.

Accommodation, Ocular↗
PubMed1985

Infant astigmatism and meridional amblyopia.

The orientation preferences of 70 infants aged 7 to 53 weeks with significant astigmatism [1.0 or more diopters (D)] were measured using a preferential looking procedure with paired gratings. The preference data show the consequences of the blurring effects of astigmatism when these are not compensatable by accommodation. Data from infant astigmats tested with optical correction look like those of nonastigmats. We have found no evidence for the development of meridional amblyopia during the first year of life.

Accommodation, Ocular↗
PubMed1985

Effect of pupil size on steady state accommodation.

Experiments are described in which monocular accommodation response/stimulus curves were measured with Snellen targets over the stimulus range from +1.0 to -5.0 D, using artificial pupils with diameters of 1.0, 1.5, 2.0, 2.5 and 3.0 mm and a constant retinal illuminance of 600 td. The results agree with those of earlier authors in showing a diminished response with smaller pupils. The slopes of the quasi-linear central portions of the response/stimulus curves are well described in terms of a geometrical optical approximation in which the accommodation system works to produce a retinal blur circle whose diameter is a linear function of the dioptric difference between the magnitudes of the stimulus and the accommodative resting state, this blur circle diameter being independent of the pupil diameter. Further consideration of diffractive effects suggests that contrast changes in the intermediate spatial frequency components (approximately 5 c/deg) of the retinal image may play a dominant role in guiding the response.

Accommodation, Ocular↗
PubMed1985

Growth of the visual system in the African cichlid fish, Haplochromis burtoni. Accommodation.

We have both measured directly and computed the amplitude of accommodation as a function of fish size to discover how the accommodative process changes during growth in the African cichlid fish, Haplochromis burtoni. We found that accommodation is achieved by lens movement in the pupillary plane along the naso-temporal axis. Accommodative lens movement is thereby directed toward a region of retinal specialization characterized by higher density of all cell types (except rods) in H. burtoni. When relaxed, the temporal retina is focused for near vision and active accommodation through lens movement adjusts the focus in the temporal retina for far vision. As the animal grows, the near and far focus points change appropriately for the fish size.

Accommodation, Ocular↗
PubMed1985

On Pulfrich-illusion eye movements and accommodation vergence during visual pursuit.

When the Pulfrich illusion is perceived with stationary fixation, and visual pursuit of the pendulum is then initiated, rapid vergence changes occur which correspond to the illusory elliptical path. During steady-state visual tracking of the illusion, however, the eyes move along a planar path without systematic changes in vergence. These latter pursuit movements with monocular filter involve large fixation disparities relative to unobstructed vision (0.5 degree to 1 degree divergence); hence, it is proposed that the planar tracking path probably results from strong dominance of the oculomotor system by stimuli from the unobstructed eye. During visual tracking with monocular filter and a target moving along a nonillusory elliptical path in depth, appropriate changes in vergence occur, but comparable vergence changes also arise when the target is fully hidden from one eye. This response apparently represents a superposition of accommodation vergence upon smooth pursuit movements; similar responses also occur during monocular tracking of a target moving around a circular path in depth.

Accommodation, Ocular↗
PubMed1985

Viewing distance and the sustained detection of high spatial frequency gratings.

Although conventional visual acuity tests measure the ability to resolve fine detail, many visual tasks demand prolonged detection. By evaluating the ability to maintain visual resolution, we observed that detection of stimuli subtending a small but constant visual angle depends on viewing distance and is probably determined by accommodative control. Detection was longest when viewing distance corresponded to the individual observer's accommodative resting, or tonus, position and fell off markedly for further distances. Since most visual assessment procedures involve a momentary detection criterion, they will not predict the ability to sustain accommodation and may thus overestimate visual resolution for prolonged viewing tasks.

Accommodation, Ocular↗
PubMed1985

Magnitude and rate of accommodation in diving and nondiving birds.

Accommodation was measured in a variety of waterfowl by projecting parallel low power helium-neon laser beams through the pupils of excised eyes placed in saline. The posterior globe was removed, allowing the beams, refracted only by the lens, to focus well behind the eye. Electrical stimulation of the ciliary muscle results in accommodative movement of the focal point toward the eye. Study of video recordings show that diving ducks (Mergus cucullatus and Bucephala clangala) can accommodate the 70-80 D needed to focus light on the retina when the eye is in water. Diving and nondiving species are compared in amount and rate of accommodation.

Accommodation, Ocular↗
PubMed1985

Contrast and accommodation in amblyopia.

Steady-state accommodation as a function of sinusoidal and square-wave grating contrast was measured in amblyopes. The amblyopic eyes exhibited reduced average response levels and required greater contrast to sustain accommodation than the fellow dominant eye or the eyes of visually-normal control subjects. Following therapy, accommodation in the amblyopic eye markedly improved. These results suggest: reduced accommodative controller gain, reduced stimulus effectiveness of target contrast, and considerable residual visual system plasticity with respect to the neurological control pathways of accommodation, in the amblyopic eye.

Accommodation, Ocular↗
PubMed1986

Modulation dependence of the accommodation response to sinusoidal gratings.

The steady-state, monocular, accommodation response to sinusoidal grating targets (spatial frequencies 0.67, 2.0, 6.0 and 18 c/deg) at effective distances between 0.2 and 1.0 m was measured with a laser optometer, as a function of the grating modulation. In general, only a rather weak dependence of the response on modulation was observed. The results are discussed in terms of the theoretical modulation of the retinal image as a function of defocus. It is argued that the accommodative system usually works to produce a contrast in the grating image which is well above the detection threshold. Considerable inter-subject differences in response were observed, suggesting that a variety of strategies may be employed by different subjects when engaged upon the same voluntary accommodation task.

Accommodation, Ocular↗
PubMed1986

Natural accommodation in the growing chicken.

A new technique, Infrared Photoretinoscopy, has been employed for recording natural accommodation in the chicken. The illumination of the pupil by the fundus reflection of infrared light provided by high output light emitting diodes (I.R. LED's) was monitored on a video screen. The defocus of the eye could be calculated by evaluating the fraction of the pupil which was illuminated. It was found that: in the chick the full range of accommodation (about 17D) is present in the first day after hatching, accommodation acts completely independently in both eyes, the "near pupillary response" is weaker in younger chicks, the pupil constriction in response to light starts at higher luminance in the younger chicks the developmental decrease of the f/number is not sufficient to explain the change of the pupil reaction to light. Problems resulting from the use of drugs in order to measure the refractive state using normal retinoscopy are discussed.

Accommodation, Ocular↗
PubMed1986

Dynamic interactions between accommodation and convergence are velocity sensitive.

Aftereffects of accommodation and vergence occur following approximately 1 min of adaptation to lenses and prisms respectively. This observation can be interpreted to mean that accommodation and vergence responses have phasic and tonic components. We have examined the role that these proposed subcomponents play in mutual interactions between accommodation and vergence. Both accommodative vergence (AV) and vergence accommodation (VA) were unresponsive to low temporal frequency variations (less than 0.1 Hz) in defocus and disparity respectively. However, both AV and VA were responsive to higher temporal frequency stimuli (up to 0.5 Hz). When negative feedback to the stimulated system was cancelled electronically, both AV and VA become responsive to low temporal frequency stimuli. The ratio or gain of accommodative vergence/accommodation (AC/A) and vergence accommodation/vergence (CA/C) increased nonlinearly with stimulus amplitude. Vergence aftereffects resulted from stimulation of AV and accommodative aftereffects resulted from stimulation of VA. These results are interpreted to mean there could be a complementary relationship between the amplitude of the AC/A ratio and proposed tonic adaptation of accommodation, and between the amplitude of the CA/C ratio and proposed tonic adaptation of vergence. A low saturation limit or stimulus window for tonic adaptation may account for the amplitude dependent nonlinearities of the AC/A and CA/C ratios.

Accommodation, Ocular↗
PubMed1986

Stimuli for accommodation: blur, chromatic aberration and size.

We investigated the frequency response of the accommodative system (0.05-1 Hz) using three stimuli: defocus blur, the effects of the chromatic aberration of the eye, and changing target size. A high-speed infrared optometer monitored accommodation while the subject viewed a target in a Badal optometer. Blur was provided by moving the target sinusoidally towards and away from the subject (1-3 D) and the size of the target was varied at the same frequency. Chromatic aberration was controlled by using either monochromatic (590 nm) or white light (3300 K). Gain and phase plots changed systematically as we varied the number of stimuli presented together. This suggests that besides defocus blur both chromatic aberration and changing size are involved in accommodative control.

Accommodation, Ocular↗