Search PubMed⌕ Search

Biomedical subjects

I J Constable

Publications and source records attributed to I J Constable.

202 records · Page 12Linked to original sources
PubMedDate not supplied

The effects of induced acute hyperglycemia in the cat on the retinal capillary blood flow.

PURPOSE: To study the effect of acute hyperglycemia on the erythrocyte flow in specific retinal capillary paths. METHODS: A technique for fluorescent labeling of a known fraction of the erythrocyte moiety of systemic blood was combined with fluorescence viewing of the retinal capillary network in live cats. This technique was developed to enable visualization of the erythrocyte flow in the retinal capillary network and used to acquire video recording of the retinal capillary erythrocyte flow in normal feline eyes. The pattern of capillary erythrocyte flow under normal blood glucose levels and normal systemic blood pressure served as baseline. Acute hyperglycemia was induced by intravenous injection of glucose while monitoring the systemic blood pressure. Two subsets of functional capillary pathways previously defined as S (simple) and C (complex) were identified in the recorded data. The relationship between erythrocyte flux in random selections of these two pathways and the level of hyperglycemia and systemic blood pressure was determined. RESULTS: Induction of acute hyperglycemia led to acute elevation of the systemic blood pressure that returned to baseline levels within few minutes, while blood glucose remained high. The capillary erythrocyte flux in S paths was significantly higher than in C paths at all values of systemic blood pressure. The capillary erythrocyte flux in the S paths was directly proportional to the systemic blood pressure whereas the flux in C paths was minimally affected by acute hyperglycemia for the systemic blood pressure range between 110 and 160 mm Hg. CONCLUSIONS: The erythrocyte flux in S paths is affected by the changes of the systemic blood pressure and these paths act as 'shunt vessels' when acute elevation of the systemic blood pressure occurs. C paths maintain stable perfusion under changing conditions, most probably in an effort to minimally alter the basic metabolic needs of the retinal tissue. Hyperglycemia per se was not responsible for changes of the cell flux in these capillary paths.

Acute Disease↗
PubMedDate not supplied

Preliminary evaluation of a hydrogel core-and-skirt keratoprosthesis in the rabbit cornea.

BACKGROUND: We developed a core-and-skirt keratoprosthesis, with both components made from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels. The identical chemical nature of both spongy skirt and transparent core assures a permanent union between them. We have previously shown that PHEMA sponges, within a certain range of pore size, can support cellular invasion and neovascularization when implanted into the rabbit cornea. The present study is the first to evaluate the behavior of the whole prosthesis after implantation into the rabbit cornea. METHODS: Hydrogel keratoprostheses were inserted intrastromally into the corneas of seven rabbits and histologically examined by light microscopy in five eyes enucleated at 8, 12, and 14 weeks. RESULTS: None of the implants extruded over this period. Both clinical and histopathologic examination showed that the keratoprostheses were well tolerated by the host tissue. The porous skirt was fully integrated into the stroma by fibrovascular invasion, and no capsule formed around the implants. Stromal melting anterior to the implant occurred in two cases, but this did not affect the fixation of the keratoprostheses. CONCLUSIONS: This study indicates that our keratoprosthesis can prevent extrusion in the short term when inserted into an intrastromal pocket of the rabbit eye.

Animals↗
PubMedDate not supplied

Bovine corneal stroma ablation rate with 193-nm excimer laser radiation: quantitative measurement.

Excimer lasers operating at 193 nm may become important surgical instruments in ophthalmology because of their ability to ablate tissue with excellent precision and minimal damage to adjacent tissue. However, the precision is limited by the accuracy of the measurement of the amount of tissue ablated per pulse at the fluence used. A measurement of the ablation rate of bovine corneal stroma over the range of fluences most likely to be useful for corneal surgery (50-400 mJ/cm2) is presented. The technique used produced reproducible results, the data from 47 animal eyes being averaged to further increase the precision. For this range of fluences, these results show a more precise measurement than previously published tissue ablation rate data. These results should be useful in accurately predicting the result of corneal surgery using the excimer laser if species differences are not major.

Animals↗