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Results for “ACCOMMODATION (OCULAR)”

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PubMed1979

Estimates of genetic correlations among clinical measures of the eye.

In a quantitative genetic investigation of seven clinical tests, five pairs were significantly correlated: (1) cover test measures and corneal power, (2) corneal power and divergence recovery points, (3) convergence and divergence recovery points, (4) divergence break and recovery points, and (5) convergence break and recovery points. Common genes may account entirely for the gene influence on cover test measure; thus, parents who are above the population mean for corneal power will have offspring with a tendency toward an exodeviation (phoria). The two convergence amplitudes may depend on the same gene differences, whereas the two divergence amplitudes only partly reflect a common function, suggesting that they may be indexing somewhat different underlying physiologic mechanisms.

Accommodation, Ocular↗
PubMed1984

Transient myopia and accommodative paresis following retinal cryotherapy and panretinal photocoagulation.

Loss of accommodation, transient myopia, or both, were complications following retinal cryotherapy in two eyes and after panretinal photocoagulation in six eyes (seven patients). A 17-year-old young man had these refractive difficulties one week after cryotherapy for retinal holes. His accommodative amplitude measured 1.0 D in the treated eye and 8.0 D in the untreated eye. One week later he received cryotherapy to the previously untreated eye, reducing that accommodative amplitude to 2.5 D. Accommodative paresis and transient myopia resolved without treatment within five weeks. Six other patients (six eyes, seven episodes) with an average age of 33 years demonstrated accommodative loss (40% to 92% decrease, average decrease 64%), transient myopia, or both, after panretinal photocoagulation for proliferative diabetic retinopathy. All patients recovered without treatment within six weeks (average, 22 days). All young patients should be made aware of this transient, but troublesome complication before treatment.

Accommodation, Ocular↗
PubMed1985

Visual function and academic performance.

Evaluation of 1,910 first-, second-, and third-grade students indicated that visual function and academic performance as measured by reading were not positively related. Visual function tests included visual acuity, muscle balance, preferred eye and hand, color vision, refraction, sensory and motor function, and a writing and drawing task. Academic tests included the Metropolitan Readiness Test, the Cognitive Abilities Test, the Iowa Test of Basic Skills, and the teacher's assessment of reading level. A simple test which can be completed during the office visit and interpreted by the ophthalmologist in the office included drawing, copying, and writing. A segment of this test, the "draw a bicycle test," can be used by an ophthalmologist to demonstrate the difference between vision and performance when examining a child up to third-grade level who is referred because of school failure.

Accommodation, Ocular↗
PubMed1986

Nonaccommodative convergence excess.

Nonaccommodative convergence excess is a condition in which a patient has orthotropia or a small-angle esophoria or esotropia at distance and a large-angle esotropia at near, not significantly reduced by the addition of spherical plus lenses. The AC/A ratio, determined with the gradient method, is normal or subnormal. Tonic convergence is suspected of causing the convergence excess in these patients. Nonaccommodative convergence excess must be distinguished from esotropia with a high AC/A ratio and from hypoaccommodative esotropia. In 24 patients treated with recession of both medial recti muscles with and without posterior fixation or by posterior fixation alone, the mean correction of esotropia was 7.4 prism diopters at distance and 17 prism diopters at near.

Accommodation, Ocular↗
PubMed1984

Episodic unilateral mydriasis and migraine.

Seven patients (all female, ranging in age from 5 to 53 years) had typical migraine and episodic unilateral mydriasis. These mydriatic episodes, usually occurring during the headache, lasted from 15 minutes to 24 hours and had occurred for three months to 35 years. Three patients had suffered from car sickness as children and there was a family history of migraine in six. Normal accommodation in five patients, normal responses to pilocarpine in two patients, and a return to normal or near-normal pupillary reaction in five patients with the cessation of headache made pharmacologic blockade unlikely. Although there are several possible neurogenic mechanisms, a parasympatholytic origin appears to be the most likely explanation for the mydriasis. Such episodes are generally benign.

Accommodation, Ocular↗
PubMed1975

Spectral analysis of the EEG recorded during stimulation of the human fovea.

Computer spectral analysis was performed on the EEGs of 6 subjects recorded during monocular foveal stimulation. Stimulus wavelength and subjective brightness were varied independently to determine their importance to changes in the ongoing EEG. The contribution of oculomotor control to these effects and the retinal area of their origin were also investigated. The major results were as follows. (1) Stimulation of the fovea reduced the amplitude of the EEG and the coherence between hemispheres at all frequencies, but most dramatically in the alpha band. (2) It increased the variance of EEG amplitudes and widths of spectral peaks in the alpha band and shifted these peaks to lower frequencies. (3) Auto-spectral intensities in the alpha band were enhanced slightly at brightness levels near photopic threshold, but were unaffected by changes in stimulus wavelength. (4) The fovea appeared to be the most effective retinal area in which irradiation attenuated ongoing alpha activity.

Accommodation, Ocular↗
PubMed1978

The cerebellar control of accommodation of the eye in the cat.

The effect of cerebellar stimulation on the accommodation of the lens was examined in anesthetized cats. An infrared optometer was used to measure the refractive power of the lens during stimulation of the cerebellum. The area giving responses within latencies shorter than 160 msec and amplitudes larger than 0.15 diopters is localized in the contralateral interpositus and fastigial nuclei and the ipsilateral interpositus nucleus. No responses could be evoked by stimulating the bilateral lateral nuclei. Accommodation responses were also evoked by cerebellar cortex stimulation. Accommodation responses evoked by stimulating the cerebellar nuclei were inhibited by preceding cerebellar cortical stimulation.

Accommodation, Ocular↗
PubMed1980

Efferent discharge patterns in the ciliary nerve of rabbits and the pupillary light reflex.

Unitary discharges in the efferent ciliary nerves were studied in cervical sympathectomized rabbits. In all, 279 units were recorded and categorized, except 7 units, into the following 3 types from their responses to photic and other stimuli, i.e. type A (170 units), type B (42 units) and type C (60 units). Type A units were characterized by exhibiting excitatory response to ipsilateral eye illumination and the response was closely related to the luminance level. The type A was further classified into AI (excitation), AII (no change) and AIII (inhibition) on the basis of the response to contralateral illumination. It was inferred that the type A was functionally related to active pupilloconstriction. Type B units were characterized by showing an exclusively inhibitory response to ipsilateral and/or contralateral illumination and the inhibition was luminance-dependent. It was therefore assumed that the type B was concerned with active pupillodilation. Type C units were not responsive to light stimulus, though the type C displayed characteristic reflex response to mechanical or thermal stimulus within the receptive field. The reflexive response, however, was not mediated via the oculomotor nerve. In order to confirm the results of the unit analysis, pupillary light reflex was examined. In particular, the consensual reflex varied depending upon individual rabbits. Namely, one became miotic, another mydriatic and a third remained uninfluenced, which corresponded well with the response pattern of the light-sensitive units.

Accommodation, Ocular↗
PubMed1981

Cortical neurons in and around the Clare-Bishop area related with lens accommodation in the cat.

Single-unit discharges in the cat Clare-Bishop area were correlated with spontaneous accommodation responses. No appreciable change was found in accommodation responses evoked by stimulating the Clare-Bishop area, when cerebellar outflow was blocked reversibly by cooling the superior cerebellar peduncle. It is suggested, therefore, that the Clare-Bishop area plays an important role in the lens accommodation system through a pathway independent from that of the cerebellum.

Accommodation, Ocular↗
PubMed1975

Integral control in accommodation.

Models of the accommodation system available inthe literature may be classified as proportional controller, optimal bang-bang controller and pure integral controller types. Each of these models explains only some aspects of the experimental behavior of the system and conflicts with other experimental observations. Based on two different experiments in which the built-in phyiological feedback loop has been opened, a leaky-integrator element is proposed for the accommodation controller. This element appears to resolve the conflict between the proportional and integral controller models and also explains the experimental observations better than any of the existing models.

Accommodation, Ocular↗