Biomedical subjects
Publications and source records attributed to R A Alexander.
The levator palpebrae superioris muscles from 12 cases of Marcus Gunn phenomenon were examined histologically by means of histochemistry and morphometry. The appearances were of a neurogenic atrophy with pathological changes occurring in both the affected side and the clinically normal side, suggesting that the causative lesion was located in the central nervous system.
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The presence, nature, and composition of a layer of transparent mucinous material overlying the posterior epithelium (called here, 'the viscous layer of the posterior epithelium') was investigated in material from domestic cats. A number of different techniques were used. (a) A variety of different fixatives and histochemical stains was used to preserve and visualise the layer of examination by light microscopy. Frozen sections of fresh material were also examined after on-slide fixation. The preservation and appearance of the viscous layer was critically dependent on the type of fixative used and on minimal agitation during tissue processing. It appeared to contain sulphated acid GAGs, the staining of which was histochemically masked around pH 2.5. The use of frozen sections produced the most reliable preservation of the layer. (b) Ruthenium red or cetylpyridinium chloride was used to preserve the viscous layer for examination by transmission electron microscopy. It appeared in a dispersed form after stabilisation by ruthenium red and in a condensed form after stabilisation by cetylpyridinium chloride. (c) Freeze-dried tissue was examined by scanning electron microscopy. The viscous layer usually appeared as a band of coral- or moss-like material which was often many times the thickness of the posterior epithelium. Usually, the areas of the layer adjoining the posterior epithelium and the anterior chamber appeared more condensed when compared to the material between these two regions. The physiological significance of the viscous layer is discussed.
Although the presence of mature elastic fibres in the sclera, trabecular meshwork and Bruch's membrane of the human eye has been recognized for many years, it is only latterly that the existence of the elastic-related fibres oxytalan and elaunin has been appreciated. The microfibrillar component of elastic, oxytalan, which is present in several ocular structures in infancy, can either mature to fully-developed elastic tissue or, as in the cornea, disappear in subsequent years. Deposition of elastic fibres, particularly the incomplete forms, can occur in the post-developmental period in a variety of disease states but the stimulus and functional significance in most situations is obscure. The evidence suggests, however, that the capacity to form elastic-related tissue is not confined to any one cell type.
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Unusual giant nodules on the posterior surface of Descemet's membrane were observed in two out of over 400 corneae examined during routine histopathological reporting. Both of the patients, a 60-year-old man and a 26-year-old woman, had histories of corneal trauma. Neither was associated with chronic keratitis or corneal dystrophy. Light microscopy showed these nodules to be composed of material resembling Descemet's membrane. Histochemical and electron microscopical preparations identified oxytalan fibres within the outer layers of the nodules. These fibres are not a feature of the normal adult Descemet's membrane. The findings are discussed and compared with other nodular lesions of Descemet's membrane.
A new technique for optimizing split-half reliability estimates yielded substantial and comparable increases in indexes of internal reliability for some major Rorschach variables across two diverse samples. Practical suggestions for applying this method to other projective tests were advanced. The inadvisability of computing odd-even reliability coefficients without regard to split-half distributional anomalies is addressed.
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Hand Test data from comparable sets of clinical samples were analyzed for reliability using the usual odd-even split and then also calculating all possible (126) split-half combinations. Maximum stable reliabilities were obtained which were substantially superior to the odd-even method. It was concluded that projective tests are probably more internally reliable than has heretofore been reported.
Sporadic cases of corneal opacity occurred in an SPF rabbit colony fed on a diet containing 10% white fish-meal. Routine histological monitoring also revealed atheromatous lesions involving the intima of the aorta, coronary arteries and the arteries of other organs in 29 rabbits examined. Serum cholesterol levels above 10 mmol/l were found in 7 rabbits, including 4 affected with corneal lesions, which proved to be lipid keratopathy on histochemical and electron microscopical examination. The serum cholesterol level was found to be within normal range (below 2.27 mmol/l) in 10 rabbits reared entirely on a modified version of the diet, where the 10% fish-meal content was replaced with 10% grass-meal. No more ocular or atheromatous lesions have been found since the adoption of the new diet for the colony.
The presence of shared implicit theories of performance is used in explaining the failure of behavioral anchors to improve performance ratings. It is proposed that efforts to improve rating accuracy also will be hampered by a preoccupation with observation. Instead, attention needs to be focused on the inferential accuracy of the rater and the cognitive processes and implicit theories upon which raters rely.
The histochemical staining properties of the abnormal material deposited in the anterior segment of the eye in the pseudoexfoliation syndrome and the zonular ligaments of the lens are essentially the same. Both present the staining characteristics of oxytalan, the microfibrillar component of elastic tissue. Reasons are advanced for regarding the pseudoexfoliative material as a product of the ciliary and lenticular epithelium.
A straightforward method for dealing with the effect of response productivity when comparing individual scoring categories between groups was presented along with an example. It was contended that percentage comparisons based on group data can circumvent the reliability problems associated with percentage scores derived from single protocols. Other problems connected with ratio and percentage scores were discussed.
In clinical research, test data are often encountered where groups differ in terms of total number of responses. When this occurs, conversion of component scores into percentages of R for each individual is recommended before multivariate clustering techniques are applied. An illustration of increased prediction resulting from percentage conversions is presented and other advantages of this approach are discussed.
The presence of elastic and related fibres in the corneal and limbal tissue of the domestic cat is described. Various ages of animal from birth to maturity were studied by light and electron microscopy. Oxytalan fibres were present throughout the new-born kitten cornea. They were seen in greatest concentration both at the junction of the posterior limiting lamina with the inner substantia propria and beneath the peripheral anterior epithelium. With increasing maturity, oxytalan fibres disappeared from all but the most peripheral parts of the cornea where some of the, by now, thicker oxytalan fibres had matured into elaunin. All ages of animals studied showed an abrupt increase in fibre thickness and numbers at the corneal limbus. Oxytalan fibres predominated in the newborn kitten limbus but material from adult animals showed an increased proportion of elaunin fibres. Occasional elastic fibres were also seen in the more superficial region of the adult limbus. An overall decrease in elastic fibre types with increasing maturity was most obvious in the middle limbal layers.
Completely formed elastic fibres consist of a core of amorphous elastin within a mantle of microfibrils. The fibrillar component may occur as isolated bundles (oxytalan) or may be randomly intermingled with variable amounts of elastin (elaunin). The distribution of both mature elastic and incomplete oxytalan and elaunin fibres in the different parts of 53 human eyes from foetal life to old age is described, as evaluated by light microscopy of histochemical preparations. In general elastic tissue was most evident in the collagenous structures save the adult cornea in which incomplete elastic fibres occur rarely and then late in life. Precursor forms predominate in early childhood and show a limited and slow capacity for maturation. The suspensory zonular fibres of the lens appear to be composed largely of oxytalan throughout life. There is also evidence that corneal epithelium and endothelium, irideal smooth muscle and, less certainly, retinal pigment epithelium can synthesise the fibrillar component, although not elastin, of elastic tissue.
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