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Biomedical subjects

J T Ernest

Publications and source records attributed to J T Ernest.

At least 19 recordsLinked to original sources
PubMed1995

Retinal tissue oxygen tension in normoxic cats under enflurane anesthesia.

PURPOSE: General anesthesia reduces systemic blood pressure and, thus, ocular perfusion pressure (at constant intraocular pressure). Whether this reduction in ocular perfusion pressure produces retinal hypoxia is unknown. To answer this question, the authors measured inner retinal oxygen tension in cats under general enflurane anesthesia at three clinically relevant levels of anesthesia under normoxic conditions. METHODS: Polarographic oxygen microelectrodes were used to measure inner retinal oxygen tension in cats under enflurane anesthesia at 21% inspired oxygen tension. Measurements were made in the preretinal vitreous body within 100 to 200 microns of the internal limiting membrane of the retina. Three levels of enflurane anesthesia were used: 1.2%, 2.4%, and 3.6%, corresponding to 0.5, 1.0, and 1.5 minimal alveolar concentration. Intraocular pressure of the cats was maintained at a constant normal level throughout the experiments. RESULTS: Under normoxic conditions, inner retinal oxygen tension remained unchanged or increased slightly as ocular perfusion pressure decreased with deeper levels of enflurane anesthesia. CONCLUSION: Commonly used surgical levels of enflurane general anesthesia do not cause hypoxia of the inner retina in cats breathing 21% inspired oxygen. This may be the result of preservation of retinal vascular autoregulation under enflurane anesthesia, retinal vasodilatation secondary to a direct smooth muscle relaxing effect of enflurane, or decreased retinal oxygen use under enflurane anesthesia.

Anesthesia, Inhalation↗
PubMed1992

Corticosteroid treatment for inflammatory bowel disease in pediatric patients increases intraocular pressure.

Intraocular pressure (IOP) was measured in 54 pediatric patients (aged 7-21 years) with inflammatory bowel disease (IBD) who were treated with oral prednisone for 1-104 months. The difference in mean IOP between the treated patients (mean +/- SD, 15.62 +/- 4.11 mm Hg) and 55 age-matched controls (13.83 +/- 2.42 mm Hg) was statistically significant (P = 0.007). The IBD patients were classified as group I, IOP less than or equal to 19 mm Hg in both eyes, and group II, IOP greater than or equal to 20 mm Hg in either eye. Twelve of the 54 patients (22.2%) and none of the controls had IOP greater than or equal to 20 mm Hg (P less than 0.001). Seventeen of the 54 patients (31.5%) were characterized as "steroid responders" (IOP of greater than or equal to 20 mm Hg, change in IOP of greater than or equal to 6 mm Hg between visits, or difference in IOP of greater than or equal to 6 mm Hg between the two eyes). When the dose of prednisone was reduced to 0-10 mg/day 30 days or more before measurement, 9 steroid responders showed a decrease in IOP to within 2 SD of the mean control IOP; 7 of the 9 showed a decrease in IOP of greater than or equal to 6 mm Hg. These observations indicate that while prednisone is a causative factor in increasing the IOP, susceptibility to average doses of prednisone is highly variable, and patients need to be monitored on an individual basis. Because IBD is a chronic disorder that requires prolonged corticosteroid treatment, these children are at risk of developing steroid-induced glaucoma. Careful ophthalmologic monitoring of pediatric IBD patients, as well as of other pediatric patients who receive corticosteroid therapy, is recommended.

Adolescent↗
PubMed1992

Ocular toxicity of prednisone in pediatric patients with inflammatory bowel disease.

We performed ocular examinations on 58 corticosteroid-treated pediatric patients with inflammatory bowel disease (IBD) and on 58 age-matched controls. Posterior subcapsular cataracts (PSC) were detected in 12 of the 58 treated patients (20.7%) and in none of the controls. The difference in mean intraocular pressure (IOP) between the treated patients (15.89 +/- 4.11 mm Hg) and control subjects (13.63 +/- 2.35 mm Hg) was significant statistically (P < 0.001). Twenty-one patients (36.2%) were characterized as "IOP responders" (IOP > or = 20 mm Hg, change in IOP > or = 6 mm Hg between visits, or a difference in IOP > or = 6 mm Hg between the two eyes). Formation of PSC was not correlated significantly (P > 0.05) with the total dose of prednisone, duration of treatment, average daily dose, or number of days on high doses (> or = 25 mg). Raised IOP was correlated (P = 0.005) only with average daily dose (12.4 +/- 10.9 mg/day; range, 0-47 mg/day) 30 days before examination. When the dose of corticosteroid was reduced to < 10 mg/day, 2 patients manifested regression of PSC, and 12 IOP responders showed a decrease in IOP to within 2 SD of the mean control IOP. Only 3 of the 58 treated patients (5.2%) manifested both PSC and raised IOP. A significant inverse correlation (P = 0.02) was established between IOP at first examination and formation of PSC. We propose that the mechanisms for steroid-induced lens opacities and raised IOP do not share the same genetic basis. Because 52% of these children developed either PSC or raised IOP with prednisone therapy, we advocate careful ophthalmologic monitoring of pediatric patients receiving corticosteroids for IBD or any other condition.

Adolescent↗
PubMed1991

A direct correlation of the resolution of pseudophakic cystoid macular edema with acetazolamide therapy.

We report the case of a patient with pseudophakic cystoid macular edema whose visual acuity improved promptly with oral administration of 500 mg of acetazolamide extended-release capsules BID for two weeks. However, vision worsened again within two weeks of discontinuation of the treatment. On resumption of acetazolamide therapy for three weeks, and its slow withdrawal during the following three weeks, the macular edema eventually resolved, and vision returned to normal. Our observation provides a direct correlation of the resolution of pseudophakic cystoid macular edema with acetazolamide therapy and shows the importance of tapering the doses of this regimen.

Acetazolamide↗
PubMed1988

Tissue oxygen uptake from the atmosphere by a new, noninvasive polarographic technique with application to corneal metabolism.

A standard Clark electrode has been modified to continuously monitor the PO2 in a thin, disk shaped reservoir membrane mounted on the electrode membrane surface. In vitro tests were conducted to determine the proportionality constant between the rate of change of reservoir PO2 and the flux of O2 out of the reservoir. The device was then used to determine the corneal O2 uptake on proptosed eyes of previously sacrificed rabbits. Our average measured uptake at 20 degrees C, 1.7 microliter/cm2.hr, agrees with the value 2.3 microliters/cm2.hr calculated from a diffusion analysis of the cornea utilizing literature values of the parameters at 37 degrees C for the three component layers of the cornea when they are adjusted for temperature to 20 degrees C.

Animals↗
PubMed1987

Effect of peripheral cryocoagulation on ocular blood flow.

Using the labeled microsphere impaction technique, we studied the effect of peripheral panretinal transscleral cryocoagulation in pigmented rabbits. One eye of each animal received peripheral cryocoagulation, and the fellow eye of the same animal was used as the control. Thirty-two animals received 40 exposures of peripheral cryocoagulation; twenty-six rabbits received 20 exposures. After 40 exposures of cryocoagulation, choroidal-retinal blood flow was significantly decreased when measured at one to two hours, 24 hours, and two weeks; normal flow recovered by four weeks. After 20 exposures of cryocoagulation, there was a significant reduction in choroidal-retinal blood flow at the earliest measurement time (one to two hours) only. The iris-ciliary body blood flow also was substantially decreased only at the earliest measurement time (one to two hours) and only after 40 exposures.

Animals↗
PubMed1986

Vitreous glucose in bacterial and sterile endophthalmitis.

Bacterial or sterile endophthalmitis was induced in rabbits. The vitreous glucose levels were then assayed. Severe intraocular inflammation, whether bacterial or sterile, resulted in marked lowering of vitreous glucose as compared to control levels. Moderate or mild inflammation failed to reduce the vitreous glucose. These data suggest that determination of vitreous glucose is not of value in the differentiation of bacterial from sterile endophthalmitis.

Animals↗
PubMed1985

Two-stage argon laser trabeculoplasty in open-angle glaucoma.

Forty-five adults with primary open-angle glaucoma received argon laser trabeculoplasty in two stages (180 degrees in each session) separated by one month. The indication for argon laser trabeculoplasty in each case was uncontrolled glaucoma consisting of progressive optic disk cupping and visual field loss despite maximally tolerable medication. A P value of .01 by Student's two-tailed paired t-test was used for statistical significance in the analysis of the intraocular pressure data. In most cases, the greatest reduction in intraocular pressure followed stage 1. Some patients received no additional benefit from stage 2; in other cases, the second stage was not only beneficial but provided most of the reduction in pressure. The pretreatment intraocular pressure level influenced the response to laser therapy. Patients with the highest pretreatment intraocular pressures received the most benefit. Both stages were complicated by a transient postoperative increase of 5 mm Hg or more in 12 patients (approximately 19%).

Adult↗
PubMed1985

Modelling whole blood oxygen equilibrium: comparison of nine different models fitted to normal human data.

The ability of nine different models, prominent in the literature, to meaningfully characterize the oxygen-hemoglobin equilibrium curve (OHEC) of normal individuals was examined. Previously reported data (N = 33), obtained using the DCA-1 (Radiometer, Copenhagen), and new data (N = 8), obtained using the Hemox-Analyzer (TCS, Southampton, PA), from blood samples of normal, non-smoking volunteers were used and these devices were found to give statistically similar results. The OHECs were digitized and fitted to the models using least-squares techniques developed in this laboratory. The "goodness-of-fit" was determined by the root-mean-squared (RMS) error, the number of parameters, and the parameter redundancy, i.e., correlation between the parameters. The best RMS error did not necessarily indicate the best model. Most literature models consist of ratios of similar-order polynomials. These showed considerable parameter redundancy which made the curve fitting difficult. The best fits gave RMS errors as low as 0.2% saturation. The Hill model gave a good characterization over the saturation range 20%-98% with RMS errors of about 0.6% saturation. On the other hand, good characterizations over the entire range were given by several other models. The relative advantages and disadvantages of each model have been compared as well as the difficulties in fitting several of the models. No single model is best under all circumstances. The best model depends upon the particular circumstances for which it is to be utilized.

Hemoglobins↗
PubMed1985

Hyaluronate increases intraocular pressure when used in cataract extraction.

A prospective randomised study of 26 eyes (24 patients) following uncomplicated intracapsular cataract surgery was carried out with three groups in which different agents were used to re-form the anterior chamber: air, seven eyes; sodium hyaluronate, seven eyes; and a combination of hyaluronate plus systemic acetazolamide, 12 eyes. The intraocular pressure (IOP) was measured by Goldmann applanation tonometry 16 hours before surgery and every eight hours after surgery for 72 hours. The IOP doubled in the two hyaluronate-treated groups for the first day following cataract surgery. By contrast, the IOP in the group receiving air initially decreased slightly. Throughout the study the effect of using acetazolamide was never statistically significant. After the first day and a half the differences in IOP among the three treatment groups disappeared, and the pressures returned to their preoperative values.

Acetazolamide↗