Teach your technicians to share (their expertise).
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Biomedical Engineering↗
Biomedical subjects
L L Hyde
Publications and source records attributed to L L Hyde.
Daily melatonin infusions entrain the locomotor activity of pinealectomized lizards.
Previously, it was shown that the locomotor activity rhythms of pineal-intact lizards (Sceloporus occidentalis) could be entrained to a periodicity of 24 h by 10-micrograms melatonin injections administered every other day at the same time. The present study examined the response of the circadian activity rhythm of pinealectomized S. occidentalis to daily 12-h infusions of smaller quantities of melatonin (0.1 or 5 micrograms melatonin/day). The results show that entrainment is achieved by infusion of 0.1 microgram of melatonin/day in pinealectomized lizards, as well as by 5 micrograms of melatonin/day in pinealectomized and pineal-intact lizards. Serum melatonin levels in pinealectomized lizards receiving 0.1 microgram melatonin/day (measured in the middle of the infusion period) were comparable to mid-dark levels in intact lizards. These results provide further support for the hypothesis that the pineal, via its daily rhythm of melatonin secretion, plays an important role in the circadian organization of lizards.
Animals↗
Corneal endothelial status 12 to 55 months after excimer laser photorefractive keratectomy.
PURPOSE: To investigate the long-term effect (range, 12-55 months) of photorefractive keratectomy (PRK) on the human corneal endothelium. METHODS: Specular microscopy of the central corneal endothelium was performed on 106 patients who underwent PRK to correct myopia. The duration of follow-up varied from 12 to 55 months (mean, 33 months; median, 37 months). Patients were divided in two groups: group 1 included 32 patients (35 treated eyes) with preoperative and postoperative central endothelial images; group 2 included 26 patients from group 1 and 74 additional patients with postoperative central endothelial images of the treated and untreated fellow eyes. RESULTS: In group 1, preoperative and postoperative values were as follows: mean cell density (+/- standard deviation), 2950 +/- 329 cells/mm2 and 2907 +/- 337 cells/mm2, respectively (P = 0.43); polymegathism index, 0.29 +/- 0.06 and 0.28 +/- 0.05, respectively (P = 0.38); pleomorphism index, 65.8% +/- 5.6% and 64.2% +/- 5.6%, respectively (P = 0.22); figure coefficient index, 0.86 +/- 0.05 and 0.87 +/- 0.02, respectively (P = 0.20). In group 2, postoperative values of the treated and untreated eyes were as follows: mean cell density, 2912 +/- 363 cells/mm2 and 2922 +/- 434 cells/mm2, respectively (P = 0.86); polymegathism index, 0.28 +/- 0.05 and 0.30 +/- 0.08, respectively (P = 0.04); pleomorphism index, 64.93% +/- 7.49% and 64.07% +/- 8.31%, respectively (P = 0.45); figure coefficient index, 0.88 +/- 0.03 and 0.88 +/- 0.03, respectively (P = 0.79). CONCLUSIONS: Photorefractive keratectomy caused no damage to the central corneal endothelium. Polymegathism differences in treated and untreated eyes could be attributed to modifications in corneal metabolism or to a yet unknown mechanism.
Adult↗
Effects of nightbreak, T-cycle, and resonance lighting schedules on the pineal melatonin rhythm of the lizard Anolis carolinensis: correlations with the reproductive response.
Experiments were conducted to determine if a correlation exists between any aspect of the pineal melatonin rhythm (such as its duration or phase) in the lizard Anolis carolinensis and the reproductive response to photoperiod. The rhythm of pineal melatonin content was determined in anoles exposed to nightbreak lighting protocols (10L:5D:1L:8D, 10L:10D:1L:3D), resonance lighting cycles (LD 11:13, LD 11:25), and T-cycle lighting protocols (LD 11:7, LD 11:9, LD 11:13, LD 11:15, LD 11:19) and compared with the testicular response to these lighting protocols as determined previously [Underwood and Hyde, (1990) J. Comp. Physiol. (A) 167:231-243]. Different T-cycles and nightbreak cycles elicited changes in both the duration of the melatonin peak and the phase of the melatonin peak relative to these light cycles. The response to the resonance cycle (LD 11:25) was complex, probably due to the overlapping patterns of two groups whose pineal melatonin rhythms were entrained approximately 12 hr out of phase with each other. No correlation was observed between the duration, or the amplitude, of the nocturnal melatonin peaks seen on the various light cycles and the reproductive response to these cycles. A correlation was observed between the phase of the pineal melatonin rhythm and the reproductive response. Light cycles were inductive (stimulated testicular growth) when the entrained melatonin rhythm peaked near the light-to-dark or the dark-to-light transition, but they were not inductive when the melatonin rhythm peaked during the middle third of the night. These results suggest that if melatonin is involved in the transduction of photoperiodic information in Anolis, neither the duration nor amplitude of the nocturnal melatonin pulse is involved in the measurement of day length. Instead, the phase-relationship of the melatonin rhythm to the rest of the circadian system may determine photoperiodic responsiveness.
Animals↗
Refractive complications of cataract surgery after radial keratotomy.
Four patients underwent cataract extraction with posterior chamber lens implantation several years after radial keratotomy. All four patients experienced an initial hyperopic shift caused by an early postoperative corneal flattening of greater than or equal to 1 diopter. This flattening partially regressed, leaving the patients with a mean of 0.42 diopter of persistent corneal flattening. We found the Binkhorst and the Holladay intraocular lens calculation formulas to be more accurate than the SRK II for these patients. Corneal curvature measured with the keratometer was less accurate for intraocular lens calculations than was a value derived by subtracting the refractive change induced by the radial keratotomy from the patients' keratometric measurements obtained before radial keratotomy.
Cataract Extraction↗
The surgical astigmatic ruler.
A simple device for evaluating the corneal astigmatism present at the conclusion of ocular surgery is described. Directing the coaxial light from the operating microscope through the ruler's round aperture will create an elliptical reflex from the cornea that indicates the presence of astigmatism. Successive apertures in the ruler present known elliptical light reflexes to the cornea, and the surgeon can select the aperture that converts the corneal reflex to a circular appearance. The dioptric marking of the aperture indicates the approximate value of the astigmatism on the cornea.
Astigmatism↗
The triple procedure: combined penetrating keratoplasty, extracapsular cataract extraction and lens implantation. An expanded experience.
The results of 177 triple procedures are presented from a continuous series of 197 cases recorded from 1973 to 1982. Eighty-nine percent achieved a visual acuity of 20/40 or better within a minimum followup period of six months. The complication rate was low, and usually managed medically. Subsequent major surgical procedures were required in only twelve (7%) of these cases (eight repeat keratoplasty, two retina repair, one resuture of graft incision, and one peripheral iridectomy). Subsequent minor surgical procedures were for discission of the posterior lens capsule in 50% of the medallion-style lens cases, and in 7% of the posterior chamber lens cases.
Adult↗
The triple procedure; combined penetrating keratoplasty, cataract extraction and lens implantation.
Results of combined keratoplasty, extracapsular cataract extraction and lens implantation (triple procedure) are reported for 67 eyes having at least 12 months follow-up. The average age of the patients was 73; the majority were female with a pre-op diagnosis of Fuchs's dystrophy. Post-op visual acuities were 20/40 or better in 72% of the eyes. No implants were removed and only one eye required regrafting. The discission rate was 32%; discissions were usually performed a year post-op. We feel the favorable results are due to uniform use of microsurgical extracapsular catarat extraction at the time of surgery with good capsular fixation of the lens implant.
Aged↗
Panel discussion: ophthalmological problems confronting pilots.
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Aerospace Medicine↗
Effects of melatonin administration on the circadian activity rhythm of the lizard Anolis carolinensis.
The green anole, Anolis carolinensis, is the most thoroughly studied North American lizard species, yet little is known about the circadian system of this species. Studies in several lizard species, including Anolis, support the hypothesis that the pineal organ is the site of a major circadian pacemaker that controls the phasing and frequency of circadian clocks located elsewhere. We examined the effects of exogenous administration of the pineal hormone, melatonin, to determine if the pineal secretion of melatonin could be the mechanism whereby the pineal communicates with the rest of the circadian system in Anolis. Continuous melatonin administration via subcutaneous silastic implants to pineal-intact anoles exposed to light-dark (LD) cycles 6:18 and LD 6:20 and to pinealectomized anoles entrained to LD 6:18 completely suppressed activity that preceded lights-on suggesting a direct inhibitory (masking) effect on activity. Continuous exogenous administration of lower dosages of melatonin to anoles expressing their endogenous circadian activity rhythm (free-running) in dim continuous light caused either arrhythmicity, a shortening of the free-running period, bouts of arrhythmicity and rhythmicity, or a suppression of activity. It was concluded that melatonin can affect both the expression of the activity rhythm as well as the circadian oscillator driving the activity rhythm. The results support the hypothesis that the circadian pacemaker in the pineal organ controls other (subordinate) circadian clocks via the rhythmic synthesis and secretion of melatonin.
Animals↗