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Biomedical subjects

A S Bruce

Publications and source records attributed to A S Bruce.

29 records · Page 2Linked to original sources
PubMed1989

Theoretical principles of optical pachometry.

Various configurations have been suggested for the optical measurement of corneal thickness by slit beam doubling, and corresponding ray traces have been provided to relate actual thickness to apparent thickness. In this report, a set of equations is provided which apply to the general situation in which neither the angle of illumination nor the angle of observation are aligned with or symmetrical about the normal to the cornea. An explicit solution to these equations giving true corneal thickness in terms of apparent thickness cannot be established, and an iterative procedure is used to develop a relationship for a number of different pachometer configurations. The near linearity of these relationships suggests the existence of a simple equation to relate these entities. By making appropriate assumptions, a linear approximation relating the inverse of the true thickness to the inverse of the apparent thickness is developed. An equation for determining the location of measurements of peripheral corneal thickness is also derived. The equations presented here may be generally applied to all optical pachometer configurations, can be used to estimate the relative contributions of various sources of error in pachometry and provide a basis for obtaining uniform absolute derivations of corneal thickness.

Cornea↗
PubMed1989

Hydration of hydrogel contact lenses during hydrogen peroxide disinfection.

Some hydrogel contact lenses are susceptible to changes in hydration when soaked in hydrogen peroxide solutions of acidic pH. This study uses a hand refractometer to assess the water content of four Hydrocurve Elite hydrogel contact lenses during prolonged hydrogen peroxide disinfection. A 3-week period of soaking in peroxide solution lead to a decrease in contact lens water content from 50% to approximately 30%. Full rehydration of the lenses occurred over a period of 2 days, using one rinse and two changes of the recommended sodium thiosulfate neutralizing solution.

Contact Lenses, Hydrophilic↗
PubMed1988

Dehydration of hydrogel lenses: environmental influences during normal wear.

To examine whether certain aspects of the environment can have a significant effect upon the steady-state water content of hydrogel contact lenses during normal wear, nine volunteers monitored ambient temperature, ambient humidity, and the water content of their contact lenses over a 5-day period of daily lens wear. Three subjects wore Hydron zero-6 lenses (38% nominal water content), three wore Hydrocurve II lenses (55%), and three wore Permalens contact lenses (71%). The results indicate that a knowledge of ambient temperature and humidity is of little value in predicting the water content of hydrogel lenses under normal wearing conditions, at least with respect to the range of environmental conditions encountered in the course of this experiment.

Contact Lenses, Hydrophilic↗
PubMed1986

Spectral transmittance of tinted hydrogel contact lenses.

The visible light and ultraviolet (UV) radiation transmission was measured for four different tints from two contact lens companies. It was found that luminous transmittance ranged from 60 to 82% and mean UV transmission from 15 to 74% for the lenses under investigation. Differences in luminous transmittance between the two lenses of each tint evaluated were generally within 1%, which was also the approximate accuracy of the technique.

Color↗
PubMed1977

An estimation of the fibre type compostion of eleven skeletal muscles from New Zealand White rabbits between weaning and early maturity.

Fibre types in 11 skeletal muscles from New Zealand White rabbits were differentiated on the basis of histochemical staining reactions for Ca2+-adenosine triphosphatase (Ca2+ATPase) at pH 9-4, cytochrome oxidase, succinate dehydrogenase and L-glycerol-3-phosphate:menadione oxidoreductase activities. Using these enzyme reactions it was convenient to divide muscle fibres into three main categories in 'white' muscles and two in 'red' muscles. Between weaning and early maturity most muscles showed little change in fibre type composition, particularly when Ca2+-ATPase activity was used as the criterion. Many muscles showed an uneven distribution of fibre types in transverse sections; this was particularly so in the cases of longissimus, semitendinosus, soleus and semimembranosus proprius. The methods successful in resolving fibre types in mature muscles were not so capable of resolving fibre types in neonatal muscles.

Adenosine Triphosphatases↗
PubMedDate not supplied

Corneal pathophysiology with contact lens wear.

Contact lens wear induces a wide spectrum of changes in the appearance and function of the cornea. The most salient effect of lens wear is the hypoxically induced reduction in the rate of metabolic activity of the corneal epithelium and its sequellae. Other important alterations to corneal health associated with contact lens wear may be caused by antigenic and toxic stimuli, mechanical forces, osmotic effects and carbon dioxide retention. Perhaps the most important task facing the contact lens clinician is to distinguish between an acceptable state of physiological modification and an anomalous or pathological state of hypofunction. In this article, we review the assortment of corneal changes primarily on the basis of the causative agents and time scale with reference to the physical and chemical processes leading to the observed signs or symptoms. This procedure allows a strong foundation for understanding the etiology and management principles for the variety of effects that contact lenses may have on the cornea.

Contact Lenses↗