The optics of comparative ophthalmoscopy

One factor peculiar to the practice of comparative ophthalmoscopy is the very large variation in ocular size of the animals examined, a factor which is ignored in current textbook treatments of the subject. We have computed values of lateral magnification, axial magnification, angular field of view and linear field of view for 19 species of terrestrial vertebrates. The dimensional value of a 1 diopter change in direct ophthalmoscopic focus was also determined. The anterior focal length of the eye in air and the vitreal refractive index were the intrinsic optical parameters of the animal's eye necessary for these calculations. Where these values were not available from the literature, the vitreal refractive index was assumed to be 1.336 and the anterior focal length was estimated as two-thirds of the axial length using a regression equation we derived from data in the literature. The angular field of view in ophthalmoscopy was shown to be invariant in the emmetropic eye and equal to the angular subtense of the ophthalmoscopic beam. The lateral field of view and retinal depth corresponding to a 1 diopter change in direct ophthalmoscopic focus varied directly with the anterior focal length of the eye. The remaining parameters of lateral and axial magnification varied inversely with the anterior focal length of the animal's eyes. These findings provide a basis for evaluating the relative size and significance of ophthalmoscopically viewed features in terrestrial vertebrate eyes.

Inconsistencies in the absorptive capacities of Schirmer tear test strips

The absorptive capacities of 4 commercially available tear test strips were determined and compared with 5-mm X 40-mm strips of #41 filter paper. Significant differences in the absorption of water over a given time interval were found in 3 of the groups tested. Major inconsistencies were found only within 1 lot of tear test strips from a single manufacturer. Tear test strips from this lot consisted of 2 distinct populations that were distinguishable by transillumination. Strips with widely spaced horizontal lines had the same absorptive capacity as the filter paper, whereas those with fine lines consistently absorbed less water. The clinical importance of this discrepancy was verified by comparing measurements of tear production in 6 normal dogs.

On the gekko pupil and Scheiner's disc

The four pinhole apertures of the constricted gekko pupil are an adaptation for decreasing the depth of field of the eye, while decreasing the total light flux to the retina. This may be useful for distance estimation at high light levels.

Enucleation in birds of prey

Enucleation in birds requires special consideration. Two case reports are presented as examples of 2 techniques for enucleation in raptors. The first technique utilizes a transaural approach and is suitable only in owls that have extensive external ear openings. The major advantage of this technique is that it allows complete histologic examination of the globe. The second technique is a globe-collapsing procedure that is suitable for any avian species. This technique precludes complete histologic examination.

Exploratory development and validation of a perceptual job burnout inventory: comparison of corporate sector and human services professionals

The present study investigated the efficacy of a scale designed to assess various aspects of burnout syndrome for use with corporate sector and human services professionals as prior research and scale development have focused solely on the latter. The scale was administered to two samples of professionals—one drawn from the corporate sector ( n = 150) and one drawn from a variety of human services organizations ( n = 237)—and the resulting data were submitted to factor analysis. A two-factor solution for perceived burnout emerged for the corporate sector employees while a five-factor solution emerged for the human services employees. The results are discussed in light of the applicability of the burnout scale for use in a wide variety of occupations.

Chemical modification of L-lactate 2-monooxygenase with fluorodinitrobenzene: evidence for two essential histidine residues

The modification of L-lactate 2-monooxygenase (lactate oxidase) with radioactively labeled fluorodinitrobenzene in 50 mM tris(hydroxymethyl)aminomethane (Tris)-acetate, pH 6.0, resulted in complete inactivation with the incorporation of 1 mol of dinitrophenyl per catalytic site. Analysis of acid hydrolysates using high-pressure liquid chromatography and an amino acid analyzer showed that Nim-(dinitrophenyl)histidine accounted for 95% of the incorporated label. Approximately 50% of the flavin in the modified enzyme was reduced by lactate, formed a sulfite complex, and underwent a photochemical reaction with oxalate. These results suggest that each active site in lactate oxidase contains two essential histidine residues that are modified in a mutually exclusive manner.

Visual accommodation in the flying fox (Pteropus giganteus)

The flying fox, Pteropus giganteus, possesses a papillated retina and was previously thought to lack a mechanism for active accommodation. An investigation of the anatomy and physiology of accommodation in this megachiropteran bat revealed that it has a well developed ciliary muscle and that it can actively accommodate through a range of at least 3.12 D. In addition, it was found that the origin of the retinoscopic reflex does not reside in the receptor layer of the retina, because the focus of the eye is invariant for small changes of angle of refraction.

Ocular lesions in free-living raptors

In a retrospective study, records of 931 raptors admitted to the Avian Clinic at the New York State College of Veterinary Medicine and to the Owl Rehabilitation Research Foundation were evaluated to determine the prevalence, cause, and distribution of ocular lesions. Some form of ocular lesion was identified in 135 (14.5%) birds. Of these, 90% were the result of physical injury. Collisions accounted for 33% of ocular lesions; gunshot wounds accounted for 11%. Unilateral lesions were more common than bilateral lesions, with the anterior segment being most frequently involved. Hyphema was the most common clinical finding. In a prospective study involving raptors admitted to the Avian Clinic from 1980-1982, it was found that 17 of 61 birds (28%) had some form of ocular lesion. The higher prevalence in this study was attributed to a lower proportion of juvenile cases and to increased detection of subtle lesions, especially those involving the posterior segment.