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Biomedical subjects

L C Moorhead

Publications and source records attributed to L C Moorhead.

14 recordsLinked to original sources
PubMed1992

Hydrodynamic analysis of intraocular pressure changes during anterior chamber procedures.

Variations in intraocular pressure (IOP), observed by us and other authors in closed-system anterior chamber procedures, are explained using a simple hydrodynamic analysis based on the Bernoulli equation. Calculations show that the sudden increases in IOP (pressure spikes) measured during anterior segment surgery are due primarily to the small size of the infusion cannulas and are exacerbated by high infusion rates. Accurate measurement of these IOP variations requires placement of the pressure sensors in situ and is not possible by remote pressure sensing at the infusion line or the console. This work indicates that closed-system procedures could benefit from accurate monitoring of intraoperative IOP and could use these measurements for automatic IOP control during surgery.

Animals↗
PubMed1991

Evaluation of drug treatments for proliferative vitreoretinopathy using vitreous microtensiometry.

The effectiveness of antimetabolic and anticollagen agents against proliferative vitreoretinopathy (PVR) was assessed by vitreous microtensiometry, a new technique that measures in situ the tensile strength of vitreous membranes. Two PVR models were produced in rabbits by intravitreal injection of bovine retinal pigment epithelial (RPE) or fibroblast cells, and the animals subsequently were treated with 5-fluorouracil (5-FU) and beta-aminopropionitrile (BAPN), administered alone or in combination. The fibroblast PVR model produced high-strength membranes that did not respond significantly to these therapies. The RPE model gave lower-strength membranes that showed marginally significant decreases in strength with intravitreal 5-FU and systemic BAPN treatments. However, combination therapy showed a highly significant decrease in membrane strength and a clinically encouraging reduction in retinal detachment.

Aminopropionitrile↗
PubMed1987

The use of thiphenamil hydrochloride (Trocinate) to control wound contraction after radial keratotomy.

We studied the efficacy of a topical smooth muscle antagonist, thiphenamil hydrochloride (Trocinate), in inhibiting wound contraction in ocular tissue. Fifteen New Zealand white rabbits underwent standard eight-incision radial keratotomy (RK), and eyes were randomly assigned to treatment or control groups. As demonstrated by slit lamp corneal photographs and by ocular histology, transient inhibition of wound contraction lasted approximately one week in all treatment eyes. We conclude that thiphenamil has a temporary, but specific, effect in controlling wound contraction after ocular surgery. Smooth muscle antagonists may be useful for managing cicatricial conditions of the eye.

Animals↗
PubMed1987

Effects of beta-aminopropionitrile after glaucoma filtration surgery: pilot human trial.

Beta-aminopropionitrile fumarate, an inhibitor of collagen cross-linking, was used topically in patients after filtration surgery for difficult cases of glaucoma (aphakic, repeat surgery, neovascular). Twenty-three patients received the drug for a total treatment period of three months following surgery. The mean preoperative intraocular pressure was 40.0 +/- 14.1 mm Hg (mean +/- standard deviation). The mean postoperative pressure was 19.0 +/- 8.9 mm Hg, with the mean follow-up at 26.4 +/- 11 weeks. The overall success rate was 74%, with success being defined as an intraocular pressure of 22 mm Hg or less at the last visit. Side effects consisted primarily of stinging immediately after the medication was applied. Inhibition of collagen cross-linking may represent an alternative method to the use of injectable 5-fluorouracil to maintain patency of filtration blebs.

Administration, Topical↗
PubMed1986

Variations in intraocular pressure during closed-system surgical procedures.

True intraocular pressure (IOP) during closed-chamber anterior segment surgery and vitrectomy was measured in rabbits by inserting a miniature pressure sensor directly into the anterior chamber or into the vitreous. Infusion fluid pressure was also measured simultaneously with a sensor in the infusion line. Significant and rapid changes in IOP up to 110 mm Hg were observed during routine anterior segment and vitreous procedures. None of these IOP changes affected infusion line pressure, which was governed solely by the infusion bottle height. Furthermore, raising the infusion bottle produced minimal IOP elevation whenever fluid was flowing into and out of the eye via a surgical instrument or a wound. These results show the limitations of monitoring of infusion line pressure as a means for assessing IOP and stress the need for IOP control during surgery.

Animals↗
PubMed1984

Effects of topical treatment with beta-aminopropionitrile after radial keratotomy in the rabbit.

This study assessed the effect of beta-aminopropionitrile treatment on the long-term curvature and compliance of corneal tissue subjected to radial keratotomy (RK). beta-Aminopropionitrile is known to inhibit cross-linking of collagen and is expected to enhance the flexibility of scar tissue, thereby reducing wound contracture and regression after RK. Seventeen adult New Zealand rabbits, weighing about 4.5 kg each, underwent RK in both eyes (eight incisions, 90% deep, 3-mm pupillary zone). Their mean preoperative corneal curvature was 44.25 diopters (+/- 0.32D at 95% confidence level). Nine of the rabbits were treated topically with beta-aminopropionitrile ointment (33 weight % in petroleum three times daily), while the control group received the petrolatum base only. The remainder of the animals received bland petrolatum gel as a control. The animals were given periodic keratometric examinations and were killed after six to eight weeks. At that time, the beta-aminopropionitrile group showed a mean reduction of 1.85 +/- 0.13 D in corneal curvature, compared with 1.18 +/- 0.08 D in the control group. The compliance and strength of the corneas were measured in vitro immediately after death. In the pressure range from 10 to 40 mm Hg, the beta-aminopropionitrile-treated corneas changed in curvature by an average of 1.4 D as compared with 0.5-D flattening for the controls. These results indicate the effectiveness of beta-aminopropionitrile treatment in enhancing longterm compliance and reducing refractive regression after RK.

Administration, Topical↗
PubMed1983

Enzyme-assisted vitrectomy with bacterial collagenase. Time course and toxicity studies.

Electron microscopic analysis of intravitreal strands produced by the injection of autogenous fibroblasts showed thin, immature collagen after two weeks and the mature banded variety after four weeks. With the use of this intravitreal strand model, it was found that highly purified bacterial collagenase caused extensive digestion of scar tissue after incubation periods of 10, 15, and 30 minutes. There was no morphologic damage to cicatricial cellular elements or to the inner limiting membrane of the retina. A 45-minute exposure of retinas previously injured by photocoagulation to collagenase also did not result in morphologic evidence of damage. The use of collagenase as an adjunct to vitrectomy in cases of extreme vitreal scarring or retinal traction may decrease the complication rate of a procedure that is still extremely hazardous.

Animals↗
PubMed1983

Effects of beta-aminopropionitrile after posterior penetrating injury in the rabbit.

Beta-aminopropionitrile, an inhibitor of collagen cross-linking, effectively limited the degree of posttraumatic vitreous proliferation in rabbits three weeks after double perforating injury. Light microscopic examination of the sites of perforating injury after five weeks showed minimal intravitreal fibrous proliferation in treated animals. Electron micrographs of the cicatricial vitreous collagen showed fragmentation of collagen into smaller fibrils and disintegration into amorphous areas. Inhibition of collagen cross-linking may undermine the strength of the vitreous scaffold by making vitreous and cicatricial collagen more sensitive to tissue collagenases produced during inflammation. The failure of fibrovascular membranes to grow into the vitreous may be a secondary effect of weakened vitreous support.

Aminopropionitrile↗
PubMed1980

Bacterial collagenase. Proposed adjunct to vitrectomy with membranectomy.

Clostridiopeptidase A digested preretinal cicatricial tissue without causing morphological alteration of normal retina during a 30-minute incubation in the rabbit. Light and transmission electron microscopy were used to determine effects on the inner limiting membrane and retinal ganglion and Müller's cells and to evaluate enzyme digestion of preretinal scarring. Removal of the injected collangenase by vitrectomy resulted in normal electroretinograms and retinal morphology 48 hours postoperatively. If the enzyme was left in the eye for 24 hours, lens opacities, partial erosion of the inner limiting membrane, and extensive hemorrhage resulted. The specificity of action of the collagenase is due to the high degree of purity of the enzyme used and a substantial biochemical difference between scar collagen and basement membrane collagen. The injection of purified collagenase capable of digesting vitreal scar tissue while leaving the retina undamaged could represent a new approach to vitrectomy, specifically to facilitate certain cases of membranectomy.

Animals↗
PubMed1979

The effects of intravitreal irrigation during vitrectomy on the electroretinogram.

Intravitreal irrigation with Balanced Salt Solution Plus (BSS Plus) produced less decrease in b-wave amplitude than either normal saline solution or Balanced Salt Solution. BSS Plus was more suitable for intravitreal irrigation because it contained the appropriate bicarbonate, pH, and ionic composition necessary for maintenance of normal retinal electrical activity, and it contained glutathione, which is necessary for maintenance of endothelial cell adenosine triphosphatase and for protection against free radical damage and oxidative stress.

Animals↗
PubMedDate not supplied

Enzyme-assisted vitrectomy with bacterial collagenase. Pilot human studies.

Clostridiopeptidase A, a bacterial collagenase, was used to assist vitrectomy with membrane stripping in six patients with dense intravitreal fibroproliferative tissue associated with retinopathy of prematurity, diabetic retinopathy, or proliferative vitreoretinopathy. When it was injected intra-operatively, allowed to incubate for 15 minutes, and then removed by irrigation/aspiration, no side effects of lens opacity, lens dislocation, or retinal hemorrhage were observed. Use of this enzyme may facilitate removal of fibroproliferative tissue in certain difficult vitrectomy cases.

Adolescent↗