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Results for “ACCOMMODATION (OCULAR)”

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At least 1,045 records · Page 58Linked to original sources
PubMed1989

Functional morphology of accommodation in the raccoon.

The raccoon (Procyon lotor) is a small carnivore which eats in the upright position, using hand- and finger-like front paws and digits to wash, hold and examine its food at close range. These anatomic and behavioral characteristics prompted structural and functional studies of the accommodative capability of this species. By light and electron microscopy, we observed a prominent ciliary smooth muscle and zonular apparatus. When stimulated by carbachol or pilocarpine, the muscle and zonular apparatus exhibited a shift from longitudinal to reticular or circular orientation of some ciliary muscle bundles, anterior movement of the muscle as a whole, and more oblique crossing of the zonular fiber bundles in the zonular plexus. Maximum carbachol-induced accommodative amplitude measured by coincidence refractometry ranged from 3 to 19 diopters in these 1 to 9 yr old animals, with no definite age-accommodation relationship. A-scan ultrasonographic biometry showed that during accommodation the lens thickened very little, if at all, but moved anteriorly, while the apparent cornea to retina distance increased slightly. The raccoon thus exhibits the greatest accommodative capability of any non-primate terrestrial mammal so far studied.

Accommodation, Ocular↗
PubMed1990

Dissociation between the effect of aceclidine on outflow facility and accommodation.

The dose/effect relationships for intracameral doses of aceclidine HCl and pilocarpine HCl on total facility of outflow and accommodative amplitude were compared in the cynomolgus monkey eye in vivo. The largest dose of aceclidine tested (20 micrograms), resulted in an average increase of 270% in outflow facility, whereas accommodation was limited to an average of 5 diopters. In contrast, 20 micrograms of intracameral pilocarpine (which is submaximal in increasing facility) resulted in an average of 19 diopters of accommodation. These results provide further evidence for a dissociation between the accommodative and outflow facility functions of the ciliary muscle.

Accommodation, Ocular↗
PubMed1990

Histochemical differences within the ciliary muscle and its function in accommodation.

During accommodation, the ciliary muscle is known to move forward-inward. This movement depends on the stiffness of the ciliary muscle connections with the scleral spur. These connections are mediated by the tips of the meridional muscle. If the tips are weakened by pharmacological or surgical means, accommodation suffers. For normal accommodation, it is therefore necessary that the tips stiffen before the contraction of the main part of the muscle. We have therefore looked at the primate eye for enzymatic and ultrastructural differences between the tips and the bulk of the muscle viz, the reticular and circular portion. Myosin ATPase was stained after either alkaline or acid preincubation. Lactate dehydrogenase (LDH), succinic dehydrogenase (SDH), NADH-tetrazoliumreductase (TR) and lipids were stained using conventional methods. The results of the enzyme staining were a modest difference between the meridional tips and the bulk. The tips stained stronger for ATPase following both preincubation methods, and for LDH, whereas the bulk cells stained stronger for SDH, NADH-TR and lipids. The tips contained fewer mitochondria and more myofibrils. In all these respects, the tips of the meridional muscle resemble the fast fibers of striated muscle.

Accommodation, Ocular↗
PubMed1986

Dynamics of accommodation: measurements for clinical application.

Accommodation dynamics have not been used in clinical diagnosis as have eye movement and pupillary dynamics; the difficulty of clinical observation is matched by limitations in measurement methods. An instrument suitable for clinical use is described that allows measurement of step response latencies and especially time constants. With computer analysis, phase plane trajectories, and noise spectra can be quickly obtained also. The utility of these dynamical parameters for clinical diagnosis is illustrated by a study of changes of time constants with age in prepresbyopia.

Accommodation, Ocular↗
PubMed1995

Seronegative myasthenia gravis associated with atonic urinary bladder and accommodative insufficiency.

We report a 20-year-old female with generalized myasthenia gravis (MG) who developed atonic urinary bladder and accommodative insufficiency. Although her sera did not contain antibodies to either nicotinic acetylcholine receptor (AChR) or voltage-gated calcium channels, a positive intravenous edrophonium test and a waning phenomenon on electromyographic studies indicated a diagnosis of seronegative MG. Myasthenic symptoms as well as urinary incontinence and impaired near vision disappeared with slight sequelae after corticosteroid therapy and total removal of the hyperplastic thymus. These symptoms recurred during a tapering course of corticosteroids, and improved again with an increased dose. Therefore, in this patient, the neuromuscular transmission of muscarinic type of AChR in the smooth muscles was also affected. This patient provides insight into the mechanisms by which some smooth muscles are involved in MG.

Accommodation, Ocular↗