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Biomedical subjects

T A Meredith

Publications and source records attributed to T A Meredith.

At least 19 recordsLinked to original sources
PubMed1995

Vitreous cavity penetration of ceftazidime after intravenous administration.

PURPOSE: Penetration of ceftazidime, a third generation cephalosporin, into the vitreous cavity after intravenous administration was investigated. METHODS: Because antimicrobial penetration varies with surgical status of the eye and with inflammation, studies were conducted in phakic, aphakic, and aphakic, vitrectomized eyes in both normal and inflamed conditions. Ceftazidime 50 mg/kg was administered every 8 hours and vitreous cavity concentrations were tested at intervals from 2 to 72 hours after the initial dose. RESULTS: No penetration was found into control phakic and aphakic eyes, but drug concentrations were detected in inflamed eyes at 24 hours. Vitreous concentrations of ceftazidime in aphakic, vitrectomized eyes reached levels well above the minimal inhibitory concentration (MIC) for Pseudomonas organisms within 2 hours of intravenous administration in control eyes (8.5 micrograms/ml) and inflamed eyes (35.4 micrograms/ml). Inflammation and removal of the lens and vitreous significantly enhanced ceftazidime penetration at all time periods tested. CONCLUSION: Ceftazidime penetrates into the vitreous cavity of inflamed eyes after intravenous administration and achieves concentrations above the MIC for Pseudomonas organisms. Penetration is greatest in aphakic, vitrectomized eyes.

Animals↗
PubMed1995

Vitrectomy for vitreomacular traction syndrome with macular detachment.

PURPOSE: To describe the clinical characteristics of the vitreomacular traction syndrome with macular detachment and to report our surgical experience with this condition. METHODS: A retrospective chart and photographic review was performed on nine patients (nine eyes) who had a symptomatic decrease in visual acuity from a macular traction retinal detachment caused by vitreomacular traction syndrome. Vitrectomy was performed in each eye to reattach the retina. RESULTS: Intraoperative observation confirmed partial posterior vitreous separation with adherence of the posterior hyaloid to the detached retina and separation of the posterior hyaloid from the attached retina. After surgery the macula was reattached in seven eyes (78%). Visual acuity was improved in four eyes, stable in four eyes, and worse in one eye. CONCLUSION: Macular detachment may occur secondary to vitreomacular traction syndrome. Although the retina may be reattached surgically in these cases, visual improvement may be limited by chronic detachment, premacular fibrosis, cystoid macular edema, or macular schisis.

Aged↗
PubMed1994

Symptomatic choroidal neovascularization in blacks.

OBJECTIVE: To acquire descriptive clinical information regarding choroidal neovascularization (CNV) in black Americans. DESIGN: Retrospective review of 1308 fluorescein angiograms obtained during a 4-year interval. Color photographs and clinical records of all black patients with angiographically apparent CNV were subsequently reviewed. SETTING: Retina service of an inner-city county hospital in Atlanta, Ga, serving a predominantly black population. RESULTS: Thirty blacks with CNV (36 of 59 eyes) were identified, 26 (87%) of whom were female. Active, exudative neovascularization was present in at least one eye of 21 patients (70%). Patients were assigned to one of four diagnostic groups for analysis. Group 1 was made up of 13 patients (43%) with age-related macular degeneration with CNV. Women outnumbered men 5.5:1. Choroidal neovascularization was peripapillary in seven (54%) of these 13 patients. Group 2 was made up of six patients (20%) with idiopathic CNV, which was peripapillary in all eyes. Group 3 consisted of three women (10%) with idiopathic polypoidal choroidal vasculopathy. Group 4 was composed of eight patients (27%) with secondary CNV. The CNV was peripapillary in three (33%) of nine eyes, and women outnumbered men 7:1. CONCLUSIONS: The spectrum of neovascular maculopathy in blacks in the current study differed from that typically seen in whites, both clinically and demographically. Clinically, CNV was most commonly juxtapapillary (13 [68%] of 19 patients) and unilateral (12 [92%] of 13 patients) among the age-related macular degeneration and idiopathic groups, while six (20%) of 30 patients (all older than 50 years) had CNV in the absence of drusen or other known predisposing conditions. Disciform-stage CNV in both groups was associated with a greater degree of pigment proliferation than that typically noted in whites. Demographically, female predominance (87% overall) was dramatic compared with prior studies.

Adult↗
PubMed1992

Antitumour synergism between non-toxic dietary combinations of isotretinoin and glucarate.

Dietary calcium glucarate (CGT) increased the activity of non-toxic levels of dietary isotretinoin against pre-established tumors in the chemically-induced rat mammary tumour model. In the range of 1.0-1.5 mmol/kg diet, isotretinoin enhanced tumour growth by 20% over a 4 week course of treatment. Tumour growth inhibition not exceeding 15% was observed only at dosages as high as 2.0 mmol/kg, i.e. in the cumulative toxicity range. Growth inhibition by 64 mmol/kg diet of CGT alone was marginal, varying from zero to 8%. In contrast, the combination of 1.0 mmol/kg of isotretinoin and 64 mmol/kg of CGT caused a reversible inhibition of tumour growth, culminating in a net decrease in tumour volume of 20%. This study documents the marginal enhancement of tumour growth by high sub-optimal concentrations of isotretinoin alone, and describes conditions for inhibition of tumour growth by sub-optimal concentrations of the natural retinoid. Related in vitro studies on retinoid sensitive and insensitive cell lines suggest that the anticancer activity of the combination is dependent on sensitivity of the cells to retinoids.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

Perforating (through-and-through) injuries of the globe. Surgical results with vitrectomy.

Fifty-one eyes of 48 patients with perforating (through-and-through) injuries of the globe were treated with vitrectomy during a 12-year period. Functional success was obtained in 32 eyes (63%), anatomic success was obtained in nine eyes (17%), and treatment failed in 10 eyes (20%). In 16 eyes (32%), 20/20 to 20/100 visual acuity was obtained; in 17 eyes (33%), 20/200 to 5/200 visual acuity was obtained; and in 18 eyes (35%), less than 5/200 visual acuity was obtained. The mechanism of injury was an important prognostic indicator of final visual outcome. Eight (62%) of 13 eyes that sustained knife or nail injuries achieved a final visual acuity of 20/50 or better, while only six (16%) of 38 eyes [corrected] with missile injuries achieved a similar level of acuity. Final visual outcome correlated well with the state of the macula and was not predicted by preoperative visual acuity. Despite improvement in surgical techniques and instrumentation, no trend toward improved visual outcomes was identified during the 12-year period.

Adolescent↗
PubMed1990

Complications of tissue plasminogen activator therapy after vitrectomy for diabetes.

Human recombinant tissue plasminogen activator (25 micrograms) was injected into seven eyes of six patients who had developed massive fibrin deposition after vitrectomy surgery for diabetes. Six eyes had developed pupillary membranes and recurrence of tractional retinal detachment from fibrin membranes, and one eye had developed only a pupillary membrane. All pupillary membranes resolved within one hour of administration of tissue plasminogen activator, and five tractional retinal detachments resolved within 24 hours. All eyes developed evidence of intraocular bleeding after tissue plasminogen activator injection. Subsequently, six of seven eyes developed recurrence of fibrin accumulation and tractional retinal detachment.

Adult↗
PubMed1990

Cefazolin levels after intravitreal injection. Effects of inflammation and surgery.

Cefazolin (2.25 mg) was injected into the vitreous cavity of phakic, aphakic, and aphakic/vitrectomized rabbits; inflamed eyes were compared to controls. Vitreous levels of cefazolin were determined at selected times from 2 to 48 hr, and the half-life was calculated. The effect of inflammation was to increase the half-life or to reduce the rate of elimination of cefazolin from the vitreous cavity. The drug was cleared substantially faster from aphakic/vitrectomized eyes than from phakic or aphakic eyes. Vitreous levels of cefazolin were above the MIC for most common gram-positive organisms causing endophthalmitis in all study groups at 24 hr, but in only the phakic inflamed eyes and in the aphakic eyes with intact vitreous at 48 hr.

Animals↗
PubMed1990

Retinal detachment in penetrating keratoplasty patients.

We reviewed the records of 23 patients who had retinal detachment after penetrating keratoplasty. Seventeen retinas (74%) were reattached successfully. Of the six failures, four patients had hemorrhagic choroidal detachment at the time of keratoplasty. When these complex retinal detachments are subtracted, 17 of 19 patients (89%) had successful retinal reattachments. Of the 17 successes, only seven patients had visual acuity of 20/200 or better. Retinal detachments after penetrating keratoplasty can be repaired with a high rate of success, but visual results remain disappointing.

Cataract Extraction↗
PubMed1990

Vitreous cefazolin levels after intravenous injection. Effects of inflammation, repeated antibiotic doses, and surgery.

We devised a standardized rabbit model of intraocular inflammation using heat-killed Staphylococcus epidermidis as the inducing organism. We applied this model to study the effects of (1) inflammation, (2) repeated antibiotic doses, and (3) surgical status of the eye on cefazolin levels in the vitreous cavity after intravenous administration. Intravenous cefazolin sodium, 50 mg/kg, was administered every 8 hours for 48 hours. Eyes were harvested for assay of vitreous cavity antibiotic levels at various intervals from 1 to 49 hours. Drug levels were compared in inflamed and noninflamed eyes under both phakic and aphakic/vitrectomized conditions. At 1 hour, levels in phakic specimens were 3.0 mg/L in inflamed eyes vs undetectable in noninflamed eyes (P less than .01), but progressively increased to 10.6 mg/L at 49 hours (P less than .02) in inflamed eyes only. Levels in aphakic/vitrectomized eyes at 1 hour were 6.7 mg/L in inflamed eyes vs 4.2 mg/L in noninflamed eyes (P less than .1), but progressively increased to 24.9 mg/L at 49 hours (P less than .001) in inflamed eyes only. Levels at 49 hours in inflamed phakic and inflamed aphakic/vitrectomized eyes were well above the minimum inhibitory concentrations for organisms termed sensitive to cefazolin. We would conclude, therefore, that repeated doses of intravenous cefazolin may play an important adjunctive role in the treatment of endophthalmitis.

Analysis of Variance↗
PubMed1990

Comparative treatment of experimental Staphylococcus epidermidis endophthalmitis.

We created experimental Staphylococcus epidermidis endophthalmitis of moderate severity in the aphakic rabbit eye by injecting 100,000 organisms of a standardized laboratory strain (ATCC 155) into the mid-vitreous cavity. This model of endophthalmitis self-sterilizes in about 4 days, but inflammatory signs continue to increase 5 to 7 days after the initial bacterial inoculum. Control eyes were compared with eyes treated with five different strategies 24 hours after bacterial inoculation: intravitreal cefazolin sodium, intravitreal cefazolin plus intramuscular corticosteroid, vitrectomy plus intravitreal antibiotics, vitrectomy plus intravitreal antibiotics and intramuscular corticosteroids, and vitrectomy plus intravitreal antibiotics and corticosteroids. Quantitative grading of inflammation and media clarity were compared at the end of weeks 1, 2, and 3 after treatment. At week 1, eyes treated with vitrectomy had significantly lower inflammatory scores; those treated with corticosteroids had significantly lower scores than those without. The two effects were independent. The best results were observed with treatment consisting of vitrectomy, intraocular antibiotics, and corticosteroids. This strategy also produced significantly more eyes with clear media at the end of week 3 than treatment with intravitreal antibiotics alone.

Adrenal Cortex Hormones↗
PubMed1990

Profound central visual loss and ocular neovascularization in idiopathic recurrent branch retinal arterial occlusion.

The authors report a 65-year-old healthy, white man who experienced a dramatic loss of central vision. Iris neovascularization, rubeotic glaucoma, disc neovascularization and subhyaloid hemorrhage developed after multiple, recurrent, idiopathic branch retinal arterial occlusions. Vitreous and perivascular inflammation were prominent associated clinical features. Systemic steroids were useful in suppressing intraocular and perivascular inflammation, yet neither steroid nor anticoagulant therapy effectively prevented recurrent occlusive episodes. Retinal neovascularization and rubeotic glaucoma were successfully managed with scatter panretinal photocoagulation. Episodic intraocular inflammation and ocular neovascularization have been noted in one-third of patients sustaining recurrent idiopathic branch retinal arterial occlusions.

Aged↗
PubMed1990

Antibacterial effects of previously infected or inflamed vitreous.

The authors investigated the ability of vitreous harvested from eyes previously infected with Staphylococcus epidermidis or inflamed with heat-killed cells of the same organism to support subsequent in vitro bacterial growth. Growth of S. epidermidis and S. aureus was not supported by previously inflamed or previously infected vitreous, but Pseudomonas aerugnosa grew in all samples. These findings suggest induction of an antistaphylococcal substance by infection or inflammation of rabbit vitreous by S. epidermidis.

Animals↗
PubMed1990

Spontaneous sterilization in experimental Staphylococcus epidermidis endophthalmitis.

We created a standardized model of endophthalmitis in the aphakic rabbit eye using a laboratory strain of Staphylococcus epidermidis of known characteristics (ATCC 155). Eyes were injected with the following number of organisms: 170, 3760, 8750, 170,000 and 460,000. Serial quantitative cultures, clinical grading of infection and histopathologic studies were performed on days 1, 2, 3, 7 and 14. Bacteria appeared to multiply rapidly during the first 24 hr with peak recovery at 8 to 24 hr. Fewer bacteria were cultured on the third day after injection, and positive cultures were rare after the third day. Inflammatory scores were initially higher with each increased number of injected bacteria and tended to increase for the first 3 to 5 days.

Animals↗
PubMed1989

Vitrectomy when asteroid hyalosis prevents laser photocoagulation.

Asteroid hyalosis is a relatively common disorder of the vitreous that rarely causes visual impairment. However, funduscopic examination and laser photocoagulation can be difficult because of reflections off the asteroid bodies. Although vitrectomy is rarely indicated for impaired visual acuity, we report three cases in which pars plana vitrectomy was necessary to permit required retinal laser photocoagulation. In two patients with proliferative diabetic retinopathy and a third patient with subretinal neovascularization marked asteroid hyalosis precluded photocoagulation by standard techniques.

Aged↗
PubMed1988

Suppression of experimental tractional retinal detachment by low-dose radiation therapy.

We used a standardized model of traction retinal detachment (TRD) created by cellular membranes in the rabbit to test the effects of low-dose radiation therapy in suppressing TRD. The vitreous and lens were removed from pigmented rabbits, and homologous conjunctival fibroblasts were grown in cell culture. After resolution of postoperative inflammation, 50,000 fibroblasts in 0.1 mL of culture fluid were injected into the vitreous cavity. Ten eyes were maintained as controls. Nineteen eyes received 6 Gy (600 rad) of x-ray irradiation one to three hours after cellular injection. Eyes were monitored weekly for three weeks with indirect ophthalmoscopy. Seven (70%) of ten control eyes developed TRD at one week; no additional TRDs were noted at weeks 2 and 3. Significantly smaller numbers of irradiated eyes developed TRD: at week 1, two (11%) of 19; at week 2, five (28%) of 18; and at week 3, five (29%) of 17.

Animals↗