A pilot study of in vivo venous pressures in the pig retinal circulation.

Retinal venous pressure was examined in six pigs using a balanced servo-nulling micropuncture technique. The mean transmural venous pressure was 0.95 mmHg (SD 1.50 mmHg). The transmural venous pressure was lower at the optic disc than away from the disc (0.32 +/- 1.46 mmHg vs 1.69 +/- 1.19 mmHg, P < 0.01). At the disc a transmural pressure of zero or less (0 to -0.5 mmHg) was demonstrated in 10/21 (48%) of the disc readings. Over an intraocular pressure range of 15-26 mmHg there was a strong correlation between intraocular pressure and retinal venous pressure (Pearson coefficient r = 0.92). The results are compatible with the Starling resistor theory of venous outflow from the eye.

Dacryocystorhinostomy in south west England.

PURPOSE: To assess the pre-operative management, surgical technique employed, success rate and patient satisfaction following surgery in patients undergoing dacryocystorhinostomy (DCR) in South West England. METHOD: Two hundred and forty-two patients who underwent DCR were retrospectively studied. A telephone questionnaire was used to assess patient satisfaction in 100 patients. RESULTS: One hundred and thirteen (46%) patients had nasolacrimal duct obstruction, half of whom had a history of dacryocystitis, 70 (29%) had canalicular obstruction and 8 (3%) had mixed blockage. The site of blockage was not known or recorded in 51 patients (22%). Seventy-five (31%) patients underwent DCR, 151 (62%) DCR with insertion of silicon tubes, 9 (4%) DCR and Lester Jones tube, and 7 (3%) canaliculodacryocystorhinostomy (CDCR). Overall an 83.5% success rate was reported by the surgeons. The success rate for patients with a history of dacryocystitis was 98%, for nasolacrimal duct obstruction 96% and for canalicular obstruction 82%. When the site of blockage was not known or recorded the success rate was 60%. Where the name of the surgeon was not recorded there was a 15% successful outcome. Eighty per cent of patients reported some improvement in their symptoms following surgery. CONCLUSIONS: DCR is an effective surgical procedure with a high rate of patient satisfaction. Pre-operative identification of the site of the blockage is likely to improve surgical outcome.

The effect of intracameral, per-operative antibiotics on microbial contamination of anterior chamber aspirates during phacoemulsification.

PURPOSE: To assess the effect of per-operative antibiotics on contamination of anterior chamber (AC) aspirates during phacoemulsification. METHODS: Two hundred and twenty patients undergoing phacoemulsification of cataract were randomly allocated to receive an irrigation infusion fluid containing either balanced salt solution (BSS) alone or BSS with vancomycin (20 mg/l) and gentamicin (8 mg/l) during surgery. Conjunctival swabs were obtained from all patients immediately before pre-operative preparation. At the end of surgery 20 ml of the AC aspirate was sent for direct and enrichment cultures. Qualitative and quantitative microbiological studies were undertaken. The chi-squared test was used to compare differences between the two groups. RESULTS: There was no significant difference between the positive culture rates of the conjunctival swabs (28 vs 27; p > 0.8). In the group that received BSS alone there were 22 (20%) positive AC aspirate cultures, 18 of which were from enrichment cultures. There were 3 positive (2.7%) cultures from the group that received antibiotics added to the BSS (p < 0.0001). CONCLUSION: The addition of gentamicin and vancomycin to the irrigation fluid during phacoemulsification results in a highly significant reduction in the microbial contamination of AC aspirates.

Peroperative microbial contamination of anterior chamber aspirates during extracapsular cataract extraction and phacoemulsification.

BACKGROUND: The normal conjunctival flora is one of the main sources of intraocular contamination during cataract surgery. The theory that the positive anterior chamber (AC) pressure during phacoemulsification (phaco), and the smaller wound utilised, might reduce the rate of contamination was studied. METHODS: The peroperative AC aspirates of 210 consecutive patients undergoing cataract surgery were assessed. In group 1, 100 patients underwent a standard extracapsular cataract extraction (ECCE). In group 2, 110 patients underwent phacoemulsification of the crystal-line lens through a scleral tunnel. AC aspirates from the Simcoe irrigation/aspiration cannula (group 1) and phaco probe (group 2) were collected and microbiological studies performed after direct and enrichment cultures. RESULTS: There were 29 (29%) positives in the ECCE group compared with 22 (20%) positive cultures from AC aspirates in the phaco group. Coagulase negative staphylococcus (CNS) was the commonest contaminant in both groups. CONCLUSION: Although there was a higher rate of AC contamination during ECCE, the difference was not statistically significant (p > 0.10, chi 2 = 2.31).

Iris metastasis: an unusual cause of anterior uveitis.

We report a case of anterior uveitis due to iris metastasis in a patient with known carcinomatosis.

Steady-state lithium blood level fluctuations in man following administration of a lithium carbonate conventional and controlled-release dosage form.

A controlled-release lithium carbonate tablet was compared to an immediate release lithium carbonate capsule in normal volunteers. These crossover studies at steady state showed that the tablet produced a smoother serum curve than the capsule with no loss of total bioavailability. Quantitatively, the capsule produced about 1.4 times more fluctuation in serum lithium values than the tablet.

Statistical aspects of comparative bioavailability trials.

The role of comparative bioavailability trials in testing for the bioequivalence of different formulations of a drug is discussed and the statistical aspects of the design and analysis of such trials are reviewed. It is suggested that the design of such trials presents no special problem but that the customary method of analysis, which tests the null hypothesis of no difference between the formulations, is irrelevant to the central purpose of such trials, which is to determine whether the formulations have essentially equivalent therapeutic effects. It is proposed that only those characteristics of the data that possess a meaningful relation to the therapeutic use of the drug should be analysed and also that estimation procedures rather than hypothesis testing techniques should be employed. Several aspects of the statistics of bioavailability trials which require further investigation are listed.

Effect of sunlight on bacterial survival in transparent air samplers.

Two types of commercially available microbiological air samplers (model STA-203, New Brunswick Scientific and All-Glass Impingers, Millipore) were used outdoors at an activated sludge treatment plant. The recovery of viable particles with both instruments was increased three- to eight-fold by shielding the trapping medium from the sun during the sampling process.

Bioavailability of cimetidine in man.

The bioavailability of parenteral cimetidine was tested in 12 volunteers in a balanced three-way crossover study. Blood levels and urinary excretion were compared after intramuscular and intravenous injection and oral administration of 300 mg of cinetidine. The results indicated that the intramuscular and intravenous routes are virtually interchangeable for parenteral cimetidine, and that the oral liquid, although exhibiting a reduced area under the blood level curve as compared with the parenteral doses, nevertheless demonstrated equivalence with respect to the time the blood level remained above 0.5 microgram per ml. The 300-mg cimetidine tablet formulation was found in another group of 12 volunteers to be bioequivalent to a 300-mg dose of oral liquid.

Symmetrical confidence intervals for bioequivalence trials.

The conventional method of setting confidence intervals for the difference of the means of two normal populations gives an interval which is not, in general, symmetrical about zero. A modification of the conventional method which leads to symmetry about zero is discussed and is recommended as particularly appropriate for use in bioequivalence trials. This modification has the effect of decreasing the "effective" length of the confidence interval, on which the decision concerning bioequivalence is based, while increasing the confidence coefficient.

Early intrauterine development: II. The rate of growth in Black and Central American populations between 10 and 20 weeks' gestation.

The application of the growth-rate standards, extablished for Caucasian embryos and fetuses in a previous report, to Black and Central American racial groups has been investigated. Comparison between menstrual age and crown-to-rump length indicated differences in the 10 to 15 weeks' gestation range. However, growth rates for the same groups were practically identical between the 15th and 20th weeks of pregnancy. This finding suggests that the actual rate of growth is closely similar in the respective ethnic groups and that apparent discrepancies reflect erroneous, or purposefully false, menstrual histories rather than dissimilar growth patterns. Largely identical rates of development were suggested by the crown-rump length to foot length to body weight interrelations among the various racial groups. A moderate, but rather predictable, deviation from the earlier established standards was noted in the crown-rump length versus foot length ratios of Black American fetuses, providing the only exception to what appears to be a practically identical rate of growth for the investigated ethnic groups in the first half of gestation. The evaluation of the results was extended to involve the effect of educational and social factors on currently available data of embryonic and fetal growth. It is suggested that heretofore unconsidered factors may affect the validity of widely quoted standards of intrauterine growth.