Estimates Of Acuity Research Articles

Visual acuity and discrimination learning in the dolphin (Lagenorhynchus obliquidens)

This experiment investigated the underwater visual acuity of one adult female Pacific white-sided dolphin (Lagenorhynchus obliquidens) by assessing its ability to discriminate between stimuli comprising one and two vertical lines presented simultaneously in a two-choice discrimination learning apparatus. The experiment was performed in two phases: an initial training phase in which a basic two-line vs. one-line discrimination was established, and a testing phase which utilized this discrimination learning in determination of visual acuity. Visual discrimination learning throughout the training phase, was unexpectedly slow and apparently highly problem-specific, despite the use of a sequence of problems designed to facilitate initial learning. During the testing phase of the study, eight two-line vs. one-line test problems, differing only in two-line gap widths were presented in a random sequence 100 times each during 10 daily sessions, at a minimal viewing distance of 45 cm. A standard psychophysical difference threshold criterion was applied to the performance data, yielding an estimate of underwater visual acuity of approximately 6′ of arc, a value roughly comparable to that for the cat in air. The results of the study are interpreted as suggesting that dolphin vision is probably sufficiently well-developed for it to be a behaviorally significant modality, but that vision may well play only a relatively minor or specialised role in the guidance of normal underwater behavior.

Glaucoma in benin-city, Nigeria

To determine the contribution of glaucoma to ocular morbidity and the different types of glaucoma seen. Medical records of all new patients attending the consultant outpatient clinics of the University of Benin Teaching Hospital, Benin city, Nigeria, over a 2-year period were reviewed. Those with a diagnosis of glaucoma were analysed. Of 1,698 new patients, 147 (8.7%) had glaucoma diagnosed. One hundred and thirteen patients (76.9%) had primary open angle glaucoma, 4 patients (2.7%) had primary angle closure glaucoma, one patient (0.7%) had congenital glaucoma, 5 patients (3.4%) had juvenile glaucoma and 24 patients (16.3%) had secondary glaucoma. Among the patients with primary open-angle glaucoma, 19 patients (16.8%) and 47 patients (41.6%) were blind using visual acuity estimation and visual field criteria respectively. Glaucoma remains a common cause of ocular morbidity worldwide as in our centre. Primary open-angle glaucoma is the most common type while primary angle-closure glaucoma remains relatively rare. Key words: glaucoma, morbidity, types, Benin City.

CRITIQUE ON THE CONCEPT OF AUDIOMETER ZERO.

Introduction IN 1963 THE International Organization for Standardization (ISO) recommended a new set of zero reference levels for pure-tone audiometers. The concern and confusion which resulted has prompted a review of concept of audiometer zero. This discussion will not be concerned with validity of ISO values. Instead, it will present reasons for a basic physical reference zero rather than one based on statistical studies of audiometric data. This type of problem is seen to be fundamental to expression of other clinical laboratory measurements, as well as hearing threshold levels. After studying many of surveys on which ISO physiologic standard is based and some that were not included, we agree that ISO values are probably best available estimate of the hearing acuity of selected young individuals, tested by appropriate methods under perfect audiometric conditions. The questions we would raise are: Is such a standard