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Biomedical subjects

A J Bron

Publications and source records attributed to A J Bron.

At least 55 records · Page 3Linked to original sources
PubMed1996

The ocular blood flow tonograph: a new instrument for the measurement of intraocular pressure in rabbits.

The Ocular Blood Flow Tonograph (OBFT) and Digilab Pneumatonograph (PTG) were calibrated for use on New Zealand White rabbits using a pressure manometer and performing tonometry at varying known pressures. The calibration experiments showed that a good correlation exists between OBFT measurements and manometric readings of IOP. Moreover, no difference between open and closed stopcock measurements were observed. Corrective equations for conversion of OBFT readings to mm Hg are documented. The OBFT was compared with the PTG and the results showed there was no significant difference between the IOP measured by either instrument in a group of rabbits displaying a range of different IOPs. Regression analysis of the data gave a slope of 0.88 and a correlation co-efficient of 0.78. The OBFT proved easier to use than the PTG under restricted lighting conditions. The OBFT was also used to measure the circadian variation in IOP and to measure the IOP after the topical application of prostaglandin E2 and various serotonergic agonists. The combined data demonstrated that the OBFT is an accurate and reliable tonometer for the measurement of IOP in rabbits.

Animals↗
PubMed1996

The penetration of topical cysteamine into the human eye.

The penetration of cysteamine into human aqueous was measured to assess its suitability as a topical agent for the prevention of radiation-induced cataract. Cysteamine drops (0.5% and 1.0%) were administered preoperatively to cataract patients every half hour, for two, four, six or eight hours. Aqueous humor was collected at the start of surgery and assayed for total free thiol. There was no significant difference in the aqueous thiol level of any of the treatment groups compared with the controls. No side effects were observed.

Administration, Topical↗
PubMed1996

Corneal dystrophies and keratoconus.

This year's reports have given us a better understanding of several dystrophies as well as improvements in diagnosis and treatment. Eight corneal dystrophies have now been mapped to specific chromosomes and of these lattice, granular, Avellino, and Reis Bückler's dystrophies map to the same region of chromosome 5q, raising the question whether they are the result of mutations in separate genes or of mutations within alleles of a single gene. Phototherapeutic keratoplasty appears to offer an advantage in the initial treatment of several dystrophies whose symptoms arise from superficial corneal change. Some success has been reported in reducing the degree of hyperopic shift that accompanies deeper ablations. Further support for the genetic basis of keratoconus comes from a study in monozygotic twins and from improvements in quantitative videokeratographic indices, which have also improved our ability to distinguish keratoconus from other topographic abnormalities of the cornea. A new hypothesis for the mechanism of keratoconus proposes that an increased expression of interleukin-1 receptors, acting through a paracrine pathway, may disturb keratocyte activity and turnover, leading to a loss of stromal mass.

Animals↗
PubMed1995

Absence of effect of simvastatin on the progression of lens opacities in a randomised placebo controlled study. Oxford Cholesterol Study Group.

AIMS: A detailed assessment of ophthalmic effects of an HMG CoA reductase inhibitor, simvastatin, was performed. METHODS: Six hundred and twenty one individuals considered to be at increased risk of coronary heart disease were randomised, following an 8 week placebo 'run in' period, to receive 40 mg daily simvastatin, 20 mg daily simvastatin, or matching placebo. Patients with a baseline corrected visual acuity better than 6/24 and without a history of cataract were eligible for detailed ophthalmic assessment at 6 months (539 patients assessed) and at 18 months (474 patients assessed). RESULTS: No significant differences between the treatment groups were detected at the 6 month or 18 month visit in the refractive condition of the eye or in the mean intraocular pressure. Nor were there clear differences in the Oxford grading system scores for various measures of the major types of cataract (cortical spokes, posterior subcapsular cataract, nuclear brunescence, white scatter) or for other morphological features visible within the lens (fibre folds or focal dots). Scheimpflug slit image photographs and retroillumination analysis of the percentage of cataract within a defined region of the lens were also performed at each visit, with no clear differences observed between the treatment groups. CONCLUSION: This single centre double blind study found no good evidence of any adverse effects of 18 months of simvastatin treatment on lens opacity formation, using a variety of validated techniques to assess cataract development. Routine clinic follow up of visual symptoms and admission to hospital for ophthalmic procedures over 5 years of treatment was also reassuring, with no excess adverse outcomes observed with simvastatin.

Adult↗
PubMed1994

Heterogeneity in ultrastructure and elemental composition of perinuclear lens retrodots.

PURPOSE: To unravel the cataractogenic process(es) leading to the birefringent lenticular bodies known as perinuclear retrodots. METHODS: Ten human lenses containing biomicroscopically verified perinuclear retrodots were systematically screened and analyzed using scanning electron microscopy and energy dispersive x-ray microanalysis to verify their ultrastructure and elemental composition. RESULTS: Three types of retrodots were distinguished, different in size, ultrastructure, and origin. Two of them contained calcium phosphate, the third probably contained calcium oxalate. All three types were separated from surrounding normal fibers and the crystalline inclusions were sequestered within membrane-lined bodies. CONCLUSIONS: Because of these observations and data found in the literature it is postulated that elevated free calcium is the initiating factor in the formation of retrodots, trapped by either oxalate or phosphate and sequestered in the retrodots. It is suggested that the oxalate is derived from ascorbate because of impaired protection against oxidative stress in the older lens. Phosphoric acid is believed to be released by calcium-induced hydrolysis of membrane phospholipids.

Calcium Oxalate↗
PubMed1993

Is cortical spoke cataract due to lens fibre breaks? The relationship between fibre folds, fibre breaks, waterclefts and spoke cataract.

Fibre folds, previously called lamellar separation of the lens, have been found by electron microscopy to be associated with fibre breaks, which are seen in vivo as the circular shades of Obazawa. This led to the present study to determine the relationship between fibre folds, fibre breaks, waterclefts and spoke cataract. All lenses with fibre folds were found to have circular shades. A few instances of circular shades without fibre folds were found, suggesting that the fibre break may be the primary pathology. It was found that circular shades occurred in association with spoke cataract only when fibre folds were also present. Thus there is no essential causal relationship between fibre breaks and spoke cataract. The occurrence of waterclefts was unrelated to the presence of the other features. The lower nasal quadrant of the lens was the most common site for the four features. The depth of spoke cataracts was found to be unrelated to the age of the patient, which makes it unlikely that accommodational stress at the time of onset of presbyopia is causative.

Age of Onset↗
PubMed1993

The lens in diabetes.

This paper reviews the changes which occur in the human lens in diabetes. They include refractive changes and cataract and age-related increases in thickness, curvatures, light scattering, autofluorescence and yellowing. The incidence of cataract is greatly increased over the age of 50 years, slightly more so in women, compared with non-diabetics. Experimental models of sugar cataract provide some evidence for the mechanism of the uncommon, but morphologically distinct, juvenile form of human diabetic cataract, where an osmotic mechanism due to sugar alcohol accumulation has been thoroughly studied in diabetic or galactose-fed rats. The discrepancy between the ready accumulation of sugar alcohol in the lens in model systems and the very slow kinetics of aldose reductase (AR) has not been satisfactorily explained and suggests that the mechanism of polyol formation is not yet fully understood in mammalian systems. The activity of AR in the human lens lies mainly in the epithelium and there appears to be a marginal expectation that sufficient sorbitol accumulates in cortical lens fibres to explain the lens swelling and cataract on an osmotic basis. This is even more so in the cataracts of adult diabetics, which resemble those of age-related non-diabetic cataracts in appearance. The very low levels of sorbitol in adult diabetic lenses make an osmotic mechanism for the increased risk of cataract even less likely. Other mechanisms, including glycation and oxidative stress, are discussed. The occurrence of cataract is a predictor for increased mortality in the diabetic.

Adolescent↗
PubMed1993

Estimation of the thickness of the crystalline lens from on-axis and off-axis Scheimpflug photographs.

Measurement of human lens biometry directly from Scheimpflug images of the anterior ocular segment may be impossible when pupil size precludes an adequate Scheimpflug view of the posterior lens surface. The authors describe a simple and accurate geometric method of overcoming this problem by estimating the true lens thickness from pairs of on-axis and off-axis Scheimpflug images. The method is validated and the variability of the estimate is quantified. This new method has utility in the study of lens biometry in subjects with large lenses whose pupils cannot be adequately dilated.

Anthropometry↗
PubMed1993

An instrument for quantifying meibomian lipid on the lid margin: the Meibometer.

An instrument, the Meibometer, is described for estimating the casual level of meibomian lipid on the human eyelid margins, adapted from a commercially-available instrument used for measurement of skin surface lipid. A loop of plastic tape is pressed onto the everted lower lid margin to lift off a blot of lipid. The resultant change in light transmission of the tape is read by a photometer. Readings are not affected by side (R or L), time of day or lid surface temperature. After cleaning lipid from the lid margins with hexane, the rate of recovery per 10 blinks, as a percentage of the pre-cleaned level, was measured as 33.7 +/- 5.8 (mean +/- SE). This rate of delivery appears to provide enough lipid for complete resurfacing of the preocular tear film with every blink. Over short periods no detectable lipid was delivered in the absence of blinking.

Adult↗
PubMed1993

The casual level of meibomian lipids in humans.

Using a modified skin surface lipid measuring instrument, the Meibometer, the amounts of meibomian lipid on the lid margins (the casual levels) of 421 subjects aged 1 to 94 years were measured. The lowest levels were found in children younger than 14 years (means +/- S.E.: males = 1.48 +/- 0.17, females = 1.53 +/- 0.17 micrograms lipid/mm2 lid margin surface) and rose with age, the highest levels being found in males aged 60-69 years (mean +/- S.E. = 3.26 +/- 0.18 micrograms lipid/mm2 lid margin surface). Male levels were higher than females in the 20-29 years age group but male and female levels became indistinguishable above the age of 50. These age- and sex-related changes differed markedly from those seen in skin surface lipid levels. The age-related changes in the casual levels of lid lipids remain unexplained although an endocrinological mechanism modified by morphological factors is considered.

Adolescent↗
PubMed1993

Morphologic characteristics and chemical composition of Christmas tree cataract.

PURPOSE: Christmas tree cataract consists of highly refractile multicolored "needles" crisscrossing the lens fibers of the deep cortex. The fact that the colors vary according to the angle of the incident light, and that in retroillumination only a dim outline of the cataract is seen, would suggest that Christmas tree cataract is a diffractive phenomenon. This study was performed to unravel the ultrastructure and chemical composition of the Christmas tree needles. METHODS: Eight lenses from donor eyes and four extracapsularly extracted lenses with Christmas tree cataract were investigated by scanning and transmission electron microscopy. The chemical composition was studied with energy-dispersive x-ray microanalysis and Raman microspectroscopy. RESULTS: Scanning electron microscope examination showed that the needles are smooth, rectangular, plate-like elements bordered by membranes and amorphous material and running crisscross through the lens. In the specimens for transmission electron microscopic examination, the needles proved to be largely dissolved, but the remains showed regular spacings of approximately 5 nm. Material identical in spacing and electron density was found in neighboring cells bound to a reticular membranous network originating from the fiber-limiting membranes. Energy-dispersive x-ray and Raman microanalysis showed that the needles have a high sulfur content and pronounced S-S, CS-SC, and C-S vibrations. The cytoplasm adjacent to the needles and reticular meshwork had an elevated Ca++ content. CONCLUSIONS: It is concluded that cystine is the most likely candidate for the Christmas tree needles and that the needles probably are formed as the result of an age-related aberrant breakdown of crystallins induced by elevated Ca++ levels.

Aged↗
PubMed1993

Topical application of serotonin or the 5-HT1-agonist 5-CT intraocular pressure in rabbits.

PURPOSE: The effect of serotonin (5-hydroxytryptamine: 5-HT) and other agonists on rabbit intraocular pressure (IOP), pupil size, and the breakdown of blood-aqueous barrier were evaluated. METHODS: Serotonin and various other agonists were applied topically to the rabbit eye, and intraocular pressure was followed over the next 3 hours using a Digilab 30D pneumatometer. RESULTS: It was demonstrated immunohistochemically that topical 5-HT reached the anterior chamber within 1 hour. Serotonin raised the IOP in a dose-dependent manner over a period of up to 4 hours, with a maximum reached between 30 minutes and 1 hour. A similar effect was observed with the 5-HT1-agonist 5-carboxamidotryptamine (5-CT). Neither tryptamine, 5-hydroxytryptophan, melatonin, gepirone, nor 5,6/5,7-dihydroxytryptamine caused any changes in IOP. Serotonin did not cause a change in pupil size or a breakdown of the blood-aqueous barrier, nor did the aqueous cAMP change significantly after topical 5-HT administration. CONCLUSIONS: The data presented suggest a role for 5-HT in the control of IOP. Previously demonstrated receptors on the iris-ciliary body and the effect of the 5-HT1-agonist 5-CT suggest that the rise in IOP may be caused partly or entirely by an increase in aqueous secretion mediated by 5-HT1-like receptors. Whether or not 5-HT has a role in altering aqueous outflow resistance remains to be seen. An effect of serotonin on other aspects of aqueous dynamics or on the extraocular muscles to cause a change in IOP cannot be excluded.

Administration, Topical↗
PubMed1992

Changes in light scatter and width measurements from the human lens cortex with age.

Light scatter and width measurements of the anterior cortical layers of the human lens were made in 50 eyes of 50 subjects using computerised linear scanning densitometry of Scheimpflug images. It was demonstrated that the amount of light scatter increased with age in all of the three major zones and that zone C3 showed the most marked increase. Most lens growth occurs in zone C2 with C3 showing little increase in width once it has become established. Zone C1 showed a tendency to decrease in width with age. In addition it was shown that the C3 zone, which is not present at birth and during early childhood, appears as a distinct layer during the second decade of life. Its scattering properties continue to increase throughout life, exceeding all other zones after approximately 30 years of age, in the absence of cataract. Possible explanations for the lens zone pattern are discussed.

Adolescent↗
PubMed1992

Plasminogen activator in human tears.

Measurements were made of the nature and levels of plasminogen activator in human tears using, as a model of inflammation, patients undergoing cataract surgery. Tissue plasminogen activator (t-PA) but not urokinase plasminogen activator (u-PA) was found in tears. A wide variation in the range of t-PA in pre-operative tears was found. In those patients not receiving per-operative subconjunctival betamethasone a significant rise in t-PA was found in tears on the first post-operative day over pre-operative levels. A significant fall was noted in those receiving per-operative subconjunctival betamethasone.

Betamethasone↗
PubMed1992

The relationship between central nuclear scatter and perinuclear retrodots in the human crystalline lens.

Retrodots are common perinuclear features of age-related cataract. Clinical observation suggested that retrodots were associated with increased nuclear scatter. To test this hypothesis, retrospective data were analysed from 78 non-diabetic subjects (118 eyes), of at least 50 years of age, who had neither subscapsular nor axial spoke opacities. Retrodots were graded using the Oxford Clinical Cataract Classification and Grading system and central nuclear scatter was assessed by image analysis of Scheimpflug photographic negatives. Regression analysis in groups was performed according to the "intra-class correlation model" either considering retrodots as a graded feature (grades 0-5) or as a dichotomous variable (present or absent). After adjusting for age (treated as a co-variate), a highly significant association (P < 10(-6) was found between retrodots and increased nuclear scatter in each analysis. It is suggested that the co-existence of these two cataract types may reflect a common cataractogenic mechanism, possibly oxidative stress.

Aged↗
PubMed1992

Biometry and auto-fluorescence of the anterior ocular segment in diabetics with and without autonomic neuropathy: a case control study.

The biometry and auto-fluorescence of the anterior ocular segment were examined in a case control study of two populations of diabetics. Cases, with diabetic autonomic neuropathy, and controls without neuropathy (forty in each group) were selected from a community based diabetic population and matched individually for age, sex, and type of diabetes. Scheimpflug and auto-fluorescence anterior segment photography were performed and analysed by digital image analysis in a masked fashion. There were differences between the groups in axial lens thickness, front radius of curvature of the lens, anterior chamber depth and lenticular auto-fluorescence. These findings are discussed in the context of the known association between autonomic neuropathy and narrow angle glaucoma, and possible common mechanisms of tissue damage in diabetes.

Aged↗