DNA Damage Levels Determine Cyclobutyl Pyrimidine Dimer Repair Mechanisms in Alfalfa Seedlings.

Ultraviolet radiation in sunlight damages DNA in plants, but little is understood about the types, lesion capacity, and coordination of repair pathways. We challenged intact alfalfa seedlings with UV doses that induced different initial levels of cyclobutyl pyrimidine dimers and measured repair by excision and photoreactivation. By using alkaline gel electrophoresis of nonradioactive DNAs treated with a cyclobutyl pyrimidine dimer-specific UV endonuclease, we quantitated ethidium-stained DNA by electronic imaging and calculated lesion frequencies from the number average molecular lengths. At low initial dimer frequencies (less than ~30 dimers per million bases), the seedlings used only photoreactivation to repair dimers; excision repair was not significant. At higher damage levels, both excision and photorepair contributed significantly. This strategy would allow plants with low damage levels to use error-free repair requiring only an external light energy source, whereas seedlings subjected to higher damage frequencies could call on additional repair processes requiring cellular energy. Characterization of repair in plants thus requires an investigation of a range of conditions, including the level of initial damage.

Soluble collagen disks for the treatment of dry eye syndrome.

We evaluated the efficacy of soluble ocular inserts made from porcine scleral collagen for the treatment of dry eye syndrome. The 22 patients enrolled in this pilot study were asked to grade their pretreatment symptoms and to document the frequency of artificial tear administration. Schirmer tests, fluorescein and rose bengal staining, and impression cytology of the conjunctival epithelium were also performed at the initial evaluation. Patients were evaluated in this fashion at 3-4, 6-8, and 18-20 weeks after initiation of treatment. We observed statistically significant improvement in symptomatology and reduced necessity for artificial tear administration. There was no significant change in rose bengal staining or impression cytology results. (The absence of objective findings suggests the possibility of a placebo effect.) These findings indicate that soluble collagen inserts may be useful in treating dry eye syndrome.

The Castroviejo square graft: a retrospective study.

We examined 19 eyes of 12 patients who had undergone penetrating keratoplasty utilizing the Castroviejo square graft technique. The visual acuities at the time of examination for inclusion in the study ranged from 20/30 to counting fingers. Of the 19 original square grafts, eight were judged clear centrally with varying degrees of peripheral stromal haze, and one was hazy. The remaining eight failed with varying degrees of irreversible corneal edema. The eight corneas obtained following repeat penetrating keratoplasty were studied with light and electron microscopy. The donor/recipient corneal stromal lamellae were continuous at the graft-host junction, particularly in the mid-stromal area. Disruptions in Descemet's membrane were present at the wound; transmission electron microscopy revealed differences in the composition of Descemet's membrane between the graft and the host. Two additional square grafts had failed, and the patients were awaiting keratoplasty. Nine of the 19 grafts were judged functionally clear, with six of the nine requiring contact lens correction.

Effect of collagen shields on corneal epithelialization following penetrating keratoplasty.

To evaluate the effects of collagen shields on corneal epithelial healing following keratoplasty, we conducted a prospective study of 89 consecutive penetrating keratoplasty patients over a 9-month period, applying collagen shields in alternate cases. Eyes were evaluated on the first and on the eighth postoperative day. The appearance of the epithelium was graded on a scale from 0 to 4. Independent variables, such as donor age, patient age, patient and donor sex, death to preservation time, and donor time in K-Sol media prior to surgery, were also evaluated. Donor corneas treated with collagen demonstrated less epithelial staining and smaller epithelial defects on the first day following surgery. The results were evaluated with a Student's t test and were found to be significant (P less than 0.001). We conclude that the application of porcine collagen shields following keratoplasty is an effective means of encouraging reepithelialization of the graft.

Use of collagen shields as a surgical adjunct.

We used porcine collagen shields combined with tobramycin, gentamicin, pilocarpine, dexamethasone, and flurbiprofen sodium in 67 cases of penetrating keratoplasty and 55 cases of cataract extraction. No adverse effects were noted from the combined use of the shields with the drug. The devices proved beneficial for protection, lubrication, enhancement of epithelialization, and drug delivery.

Monitoring heparin anticoagulation and its neutralization.

Heparin anticoagulation and its neutralization were monitored by three different techniques: a manual protamine titration, an automated activated coagulation time, and an automated protamine titration. All three techniques provided satisfactory information. The decision of which to use must be based on other considerations such as available manpower and cost of equipment. The effect of using the automated protamine titration test on heparin and protamine requirements, and on blood loss measured intraoperatively after bypass and in overnight chest bottle drainage in two groups of comparable patients undergoing coronary artery bypass operation was studied. The heparin requirements were similar (24,420 +/- 584 units, control group; 23,550 +/- 849 units, treatment group), but the protamine requirements were markedly different (429 +/- 14.7 mg, control; 258 +/- 10.4 mg, treatment; p < 0.05). There was no statistical difference in intraoperative blood loss or overnight chest bottle drainage.