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PubMed1989

The interactions between chromatic aberration, defocus and stimulus chromaticity: implications for visual physiology and colorimetry.

It has long been recognised that chromatic aberration can introduce luminance artifacts into nominally isoluminant colour stimuli. In this study the effects of chromatic aberration (along with those of defocus and stimulus spatial frequency) on the chromaticity of the retinal image are considered. Such optical effects have important methodological and functional implications for visual physiology. The "Silent Substitution" principle is a fundamental feature of modern colorimetry, being employed in both psychophysical and electrophysiological approaches to the visual system. The theoretical colour spaces introduced by MacLeod and Boynton (1979) and Derrington et al. (1984) are also ultimately based on this principle. All such applications of the silent substitution principle are sensitive to the optical effects of chromatic aberration, defocus, spatial frequency and stimulus chromaticity. The spatial acuity of the mechanisms of colour vision are appreciably lower than those of the luminance system (Mullen, 1985). In addition chromatic aberration has been shown to be a cue to ocular accommodation (Fincham, 1951). The analysis presented in this study suggests a possible explanation for these findings in terms of the ecological and computational constraints placed on the visual system by chromatic aberration.

Color Perception↗
PubMed1992

Refractive state, corneal curvature, accommodative range and ocular anatomy of the Asian elephant (Elephas maximus).

The resting refractive state of six mature, female, Asian elephants (Elephas maximus) was determined using streak retinoscopy and neutralizing video retinoscopy. The amplitude of accommodation was also measured by neutralizing video retinoscopy of two animals and the corneal curvatures of three animals was measured by photokeratoscopy. The net spherical refraction was found to be +0.23 D. No difference was observed between cyclopleged and non-cyclopleged eyes (data from three animals), nor was there any difference between right and left eyes. Nine of the twelve eyes refracted had > or = 0.5 D astigmatism. The mean corneal power, as measured by photokeratometry was 21.3 D (SD = 1.8 D). There was a tendency towards with-the-rule corneal astigmatism in our sample (mean value: 1.2 D), though it did not reach statistical significance (P = 0.06). Two elephants were examined using neutralizing video photoretinoscopy. They were able to accommodate through 3 D. Three fixed eyes from three different elephants were obtained for gross and microscopic examination. The mean axial length of the eye was 38.75 mm and the lens had an axial diameter of approx. 10 mm. The posterior sclera was thick (8.0-8.5 mm). Histologically, the cornea was comprised of five distinct layers. A thin, meridionally oriented smooth ciliary muscle was identified. Individual muscle fibers were also observed associated with the posterior trabeculae of the uveal meshwork.

Accommodation, Ocular↗
PubMed2003

Evaluation of the measurement of refractive error by the PowerRefractor: a remote, continuous and binocular measurement system of oculomotor function.

BACKGROUND/AIM: The technique of photoretinoscopy is unique in being able to measure the dynamics of the oculomotor system (ocular accommodation, vergence, and pupil size) remotely (working distance typically 1 metre) and objectively in both eyes simultaneously. The aim of this study was to evaluate clinically the measurement of refractive error by a recent commercial photoretinoscopic device, the PowerRefractor (PlusOptiX, Germany). METHOD: The validity and repeatability of the PowerRefractor was compared to: subjective (non-cycloplegic) refraction on 100 adult subjects (mean age 23.8 (SD 5.7) years) and objective autorefraction (Shin-Nippon SRW-5000, Japan) on 150 subjects (20.1 (4.2) years). Repeatability was assessed by examining the differences between autorefractor readings taken from each eye and by re-measuring the objective prescription of 100 eyes at a subsequent session. RESULTS: On average the PowerRefractor prescription was not significantly different from the subjective refraction, although quite variable (difference +0.05 (0.63) D, p=0.41) and more negative than the SRW-5000 prescription (by -0.20 (0.72) D, p<0.001). There was no significant bias in the accuracy of the instrument with regard to the type or magnitude of refractive error. The PowerRefractor was found to be repeatable over the prescription range of -8.75D to +4.00D (mean spherical equivalent) examined. CONCLUSION: The PowerRefractor is a useful objective screening instrument and because of its remote and rapid measurement of both eyes simultaneously is able to assess the oculomotor response in a variety of unrestricted viewing conditions and patient types.

Adolescent↗
PubMed1988

Identification of the teleost Edinger-Westphal nucleus by retrograde horseradish peroxidase labeling and by electrophysiological criteria.

A homolog of the Edinger-Westphal nucleus of other vertebrates is described in two species of serranid basses of the genus Paralabrax, a group possessing a wide range of ocular accommodation but lacking a pupillary reflex to light. The nucleus was found by retrograde labeling from the ciliary ganglion and lies dorsolateral to the ipsilateral oculomotor nucleus. The nucleus consists of 60 to 100 neurons with an average soma diameter of about 20 microns in animals weighing 70 to 150 g. Electrophysiological experiments support the identification. Microstimulation of the nucleus evokes contraction of the ipsilateral lens retractor muscle and slight constriction of the caudal ipsilateral iris. Multi- and single-unit recordings in the nucleus reveal spontaneous firing (about 30 spikes/s in single units), the rate of which decreases during visually-evoked lens retractor relaxations (accommodation to near stimuli). Recordings of muscle fiber activity in the lens retractor show essentially the same behavior, which suggests that the ciliary ganglion and neuromuscular junctions simply relay impulses with little if any synaptic integration. The existence of a discrete Edinger-Westphal nucleus devoted largely to accommodation makes Paralabrax a good model system for the further tracing of central accommodation control pathways.

Animals↗
PubMed2006

Citation patterns in the optometric and ophthalmologic clinical binocular vision literature.

PURPOSE: The purpose of this study is to compare citation patterns in the clinical binocular vision literature of optometry and ophthalmology. METHODS: The author conducted citation analysis of two current clinical binocular vision textbooks from optometry and two from ophthalmology and of articles published in the years 2000 to 2004 in optometry and ophthalmology journals. Topical parameters for inclusion of sources were diagnosis and management of nonstrabismic binocular vision disorders, diagnosis and management of nonpresbyopic ocular accommodation disorders, and procedures for examining such conditions. These topical parameters were chosen because they are areas in which the diagnostic procedures and treatment options available to members of the two professions are not delineated by their respective scopes of practice. RESULTS: The most frequently cited journals in the optometric publications were optometry journals (63% of citations in the optometry textbooks and 58% in the optometry journal articles). The most frequently cited journals in the ophthalmology publications were ophthalmology journals (79% of citations in the ophthalmology textbooks and 49% in the ophthalmology journal articles). Each discipline also cited a greater variety of journals from within its own field than was cited by the other discipline. The journal with the highest total number of citations was Optometry and Vision Science (280) followed by Ophthalmic and Physiological Optics (73), American Journal of Ophthalmology (68), Investigative Ophthalmology and Visual Science (62), and Optometry (61). CONCLUSIONS: Optometry and ophthalmology sources show more citations to materials from their own discipline than from their fellow discipline in the area of nonstrabismic binocular vision disorders and nonpresbyopic accommodative disorders. Reasons may include lack of awareness of the literature of the other discipline, bias toward the literature of one's own discipline, or bias against the literature of another discipline. It is also likely that the diagnostic and management strategies of the two professions are significantly different, although scope of practice would not constrain the range of strategies for the conditions chosen as the topical matter for consideration in this study. The journals found to be most frequently cited in this study should help to identify the core journals in this area of clinical binocular vision.

Adolescent↗
PubMed2006

Transdermal scopolamine for prevention of motion sickness : clinical pharmacokinetics and therapeutic applications.

A transdermal therapeutic system for scopolamine (TTS-S) was developed to counter the adverse effects and short duration of action that has restricted the usefulness of scopolamine when administered orally or parenterally. The plaster contains a reservoir of 1.5 mg of scopolamine programmed to deliver 0.5 mg over a 3-day period. A priming dose (140 microg) is incorporated into the adhesive layer to saturate certain binding sites within the skin and to accelerate the achievement of steady-state blood levels. The remainder is released at a constant rate of approximately 5 microg/hour. The protective plasma concentration of scopolamine is estimated to be 50 pg/mL. TTS-S attains that concentration after 6 hours; a steady state of about 100 pg/mL is achieved 8-12 hours after application. Yet 20-30% of subjects failed to attain the estimated protective concentration, and plasma concentrations measured in subjects who failed to respond to TTS-S were lower than in responders. These findings may explain some of the treatment failures. Overall, the product appears to be the approximate functional equivalent of a 72-hour slow intravenous infusion. A combination of transdermal and oral scopolamine (0.3 or 0.6 mg) was effective and well tolerated in producing desired plasma concentrations 1-hour post-treatment. TTS-S has proved to be significantly superior to placebo in reducing the incidence and severity of motion sickness by 60-80%. It was more effective than oral meclizine or cinnarizine, similar to oral scopolamine 0.6 mg or promethazine plus ephedrine, and the same as or superior to dimenhydrinate. The addition of ephedrine or the use of two patches did not improve its efficacy, but rather increased the rate of adverse effects. TTS-S was most effective against motion sickness 8-12 hours after application. Despite previous evidence to the contrary, a recent bioavailability study demonstrated similar intraindividual absorption and sustained clinical efficacy with long-term use of the drug. The adverse effects produced by TTS-S, although less frequent, are qualitatively typical of those reported for the oral and parenteral formulations of this agent. Dry mouth occurs in about 50-60% of subjects, drowsiness in up to 20%, and allergic contact dermatitis in 10%. Transient impairment of ocular accommodation has also been observed, in some cases possibly the result of finger-to-eye contamination. Low-dose pyridostigmine was found effective in preventing cycloplegia but not mydriasis. Adverse CNS effects, including toxic psychosis (mainly in elderly and paediatric patients), have been reported only occasionally, as have difficulty in urinating, headache, rashes and erythema. Adverse effects were not correlated with plasma scopolamine concentrations. TTS-S produced only about half the incidence of drowsiness caused by oral dimenhydrinate or cinnarizine, and a level of adverse effects similar to that found with oral meclizine. Performance is not affected by short-term use. Prolonged or repeated application may cause some impairment of memory storage for new information. However, sea studies revealed significantly less reports of a decrement in performance or drowsiness due to prevention of sea sickness. The recommended dosage is a single TTS-S patch applied to the postauricular area at least 6-8 hours before the anti-motion sickness effect is required. For faster protection, the patch may be applied 1 hour before the journey in combination with oral scopolamine (0.3 or 0.6 mg). After 72 hours, the patch should be removed and a new one applied behind the opposite ear. Its place in therapy is mainly on long journeys (6-12 hours or longer), to avoid repeated oral doses, or when oral therapy is ineffective or intolerable.

Administration, Cutaneous↗
PubMed1983

Convergence spasm--treatment by amytal interview. A case report.

Convergence spasm is manifest by intermittent occurrence of ocular convergence, accommodative spasm, and miosis. It is usually due to hysteria but can have an organic basis. Treatment has included various ophthalmologic interventions. An amytal interview was used successfully to establish a nonorganic basis for the gaze palsy and, more importantly, concomitant narcosuggestion proved to be effective treatment.

Accommodation, Ocular↗
PubMed1995

The effects of Qi-Qong ocular exercise on accommodation.

Visual-training methods in management of myopia are suggested as possibly leading to normal vision or an improvement in the refractive state. The purpose of this work was to investigate the hypothesis that a Qi-Qong ocular exercise improves visual function by training the accommodation bias. Variations of pupil size, accommodative amplitude, latency and speed of accommodative response and accommodative adaptation were evaluated objectively. The accommodative state was monitored with an objective infrared refractometer (Nidek AA-2000). Subjects were divided into two groups: experimental (n = 9), and control (n = 8). Subjects of the experimental group undertook the Qi-Qong ocular exercise for at least three years, and were able to perform the exercise smoothly and gently. Subjects of the control group had no knowledge of the Qi-Qong ocular exercise, but were given the same testing procedures as the experimental group. Results showed that Qi-Qong ocular exercise can improve the accommodative amplitude and accelerate the accommodative response slightly, but there was no effect on the latency of accommodative response. Furthermore, the level of accommodative adaptation was elevated, and the pupil became slight miotic. Therefore, the mechanism of visual improvement may undergo a great accommodative adaptation and produce a pinhole effect by miosis of the pupil. Methods of visual training can produce a false image of visual improvement from an enhanced parasympathetic response to a task, but this effect may be a factor that induces progression of myopia.

Accommodation, Ocular↗
PubMed1990

Accommodative esotropia after ocular and head injury.

Five children lost their ability for motor fusion after traumatic injury to either the eye or head. All patients had the onset of accommodative esotropia within two months of the traumatic episode. The ocular alignment of each child was controlled by the use of spectacles that corrected the accommodative requirements. These patients are unique because they did not show any evidence of accommodative esotropia before their injuries. One child developed accommodative esotropia with a high ratio of accommodative convergence to accommodation. The use of bifocal spectacles controlled the deviation for this child.

Accommodation, Ocular↗