Search PubMed⌕ Search

Biomedical subjects

G O Waring

Publications and source records attributed to G O Waring.

At least 127 records · Page 7Linked to original sources
PubMed1987

Complications of hydrogel intracorneal lenses in monkeys.

We performed 32 hydrogel keratophakia procedures in rhesus monkey corneas. Surgery was technically successful in 20 eyes. Toxic stromal keratitis occurred in five eyes because of impurities on the lenticules. Fibrosis appeared around the implant in five eyes. Two eyes showed aseptic necrosis of the inferior cornea with extrusion of the implant, attributed to exposure keratitis. Complications during surgery included faulty microkeratome incisions (three eyes) and epithelial implantation in the lamellar bed (one eye). Three lenticules decentered, one extruding through the wound, probably because the monkeys rubbed their eyes excessively. Nine of the 11 eyes with postoperative refraction data showed overcorrection or undercorrection of more than 1.00 diopter. Most of these complications could have been prevented by better technique, design, and manufacture of the lenticule or cooperation of the subjects.

Animals↗
PubMed1987

Refractive keratoplasty in monkeys using intracorneal lenses of various refractive indexes.

The refractive power of the cornea can be altered with an intracorneal lens when it is inserted within a freehand lamellar-pocket incision. The effectiveness of the implant in altering the refractive power of the cornea depends on the refractive index of the intracorneal lens, since little change in the anterior corneal curvature occurs. Thirteen nonhuman primate eyes received intracorneal lenses made of synthetic polymers with refractive indexes ranging from 1.3686 to 1.633. The lidofilcon-B hydrogel (refractive index, 1.3686) lenses created no significant alteration in the refractive power of the cornea. The polymethylmethacrylate (refractive index, 1.4900D) and polysulfone (refractive index, 1.633) lenses created a predictable and significant alteration of corneal power that increased with each implant with a successively higher refractive index. The polymethylmethacrylate lens created a refractive alteration that was approximately 31% of the lens power in air. The polysulfone lens created a corneal power alteration that was approximately 40% of the lens power in air.

Animals↗
PubMed1987

Management of pseudophakic corneal edema with reconstruction of the anterior ocular segment.

The following surgical techniques were used to treat pseudophakic corneal edema in 13 consecutive eyes: penetrating keratoplasty (13 eyes), mechanical anterior vitrectomy (ten eyes), removal of intraocular lens (13 eyes), gonioplasty with opening of peripheral anterior synechiae using a dental mirror (seven eyes), iridoplasty using a round needle (six eyes), and insertion of a replacement intraocular lens (12 eyes). The most common intraoperative complication was hemorrhage in the angle. Although the angle was open 360 degrees to the ciliary body in 12 of the 13 eyes at the end of surgery, a few peripheral anterior synechiae recurred in six eyes at six weeks. Short-term results suggest that this technique can restore the structure of the anterior ocular segment, decrease progressive peripheral anterior synechiae and glaucoma, and possibly decrease cystoid macular edema.

Cataract Extraction↗
PubMed1987

Penetrating keratoplasty for herpes simplex keratitis and keratoconus. Allograft rejection and survival.

To determine the relationship between corneal allograft rejection and failure, we studied patients who underwent penetrating keratoplasty for herpes simplex keratitis (n = 82) and keratoconus (n = 345), two frequent indications for keratoplasty in young patients, using survival analysis. For first grafts for herpes, the probability of survival was significantly less than it was for keratoconus (P less than 0.0001). For second grafts, this difference was less pronounced, and for three or more grafts, the difference in survival was not significant. The incidence of rejection episodes was similar in first grafts for herpes (16.6%) and keratoconus (18.5%) (P greater than 0.05). However, the incidence of rejection episodes in regrafts for herpes was significantly greater than in keratoconus (23.7 versus 17%, P less than 0.01). The incidence of failure after rejection episodes (first grafts and regrafts combined) was significantly greater in grafts for herpes (52.4 versus 16.2%, P less than 0.001). Because survival after multiple regrafts in both groups is poor, additional measures, such as tissue matching, may be necessary to improve the likelihood of success in these high-risk cases.

Adolescent↗
PubMed1987

Clinical results with a ceramic keratoprosthesis placed through the eyelid.

The authors placed a ceramic keratoprosthesis through the eyelids of 11 consecutive patients: six with alkali injury, four with cicatricial pemphigoid, and one with Stevens-Johnson syndrome. The surgery was technically successful in ten patients. One patient experienced an intraoperative, expulsive choroidal hemorrhage, and the keratoprosthesis was not implanted. Six patients were followed for 21 to 56 months; three, who had no postoperative potential for visual improvement were followed for 2 to 6 months; and one patient died 14 months after surgery. Six patients achieved 20/20 to 20/100 corrected visual acuity at some point after surgery. At last examination, only three eyes (27%) saw 20/200 or better. Complications included eyelid cellulitis, extrusions, aqueous leaks, retroprosthetic membranes, endophthalmitis, and progressive glaucoma. The authors think mechanical torque by movement of eyelid and globe destabilizes the keratoprosthesis, producing many of the complications.

Adult↗
PubMed1987

Survival of corneal grafts from donors supported by mechanical ventilation.

Eighty-five patients undergoing penetrating keratoplasty with tissue from donors supported by mechanical ventilation (Ventilator group) were compared to a surgeon- and diagnosis-matched group (Control group). Age at surgery, duration of follow-up, and sex of recipient patients were similar in the two groups. The mean donor age in the Ventilator group (26.4 years) was significantly less than in the Control group (45.8 years, P less than 0.0001). Mean time on the ventilator was 99.4 hours (range, 4 hours to 21 days). Overall graft survival rates in the Ventilator and Control groups were similar (P greater than or equal to 0.72). Time on the ventilator did not affect graft survival. Cultures of corneoscleral donor rims were positive more often in the Ventilator group than in Controls (39.7 versus 23.1%), but the difference was not significant (P = 0.09). Prolonged ventilator time was not associated with a higher rate of positive corneoscleral rim cultures, nor did positive cultures affect graft survival. The most common cause of graft failure in both groups was allograft rejection. In no case could postoperative bacterial infection be attributed to contamination of the donor material. One case of primary donor failure occurred in the Ventilator group, but the incidence (1.2%) is similar to that of previously reported studies. The data indicate that corneal tissue from ventilator-supported donors should be considered for use in penetrating keratoplasty.

Adolescent↗
PubMed1987

Three-year results of the Prospective Evaluation of Radial Keratotomy (PERK) Study.

The Prospective Evaluation of Radial Keratotomy (PERK) study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refractive error between -2.00 and -8.00 diopters (D). The authors report results for one eye of each patient. The surgical technique consisted of eight incisions using a diamond micrometer knife with the blade length determined by intraoperative ultrasonic pachymetry and the diameter of the central clear zone determined by the preoperative refractive error. At 3 years after surgery, 58% of eyes had refractive error within 1.00 D of emmetropia; 26% were undercorrected and 16% were overcorrected by more than 1.00 D. Uncorrected visual acuity was 20/40 or better in 76% of eyes. The operation was more effective in eyes with a preoperative refractive error between -2.00 and -4.37 D. Between 1 and 3 years after surgery, the refractive error changed by 1.00 D or more in 12% of eyes, indicating a lack of stability in some eyes. In the 435 eyes, there was a small number of complications including six eyes that lost two or three lines of best-corrected acuity, 16 that experienced vascularization of the incisions, 2 that had delayed bacterial keratitis, and 4 that had recurrent epithelial erosions.

Follow-Up Studies↗
PubMed1986

Fly larva adherent to corneal endothelium.

Anterior ophthalmomyiasis is a rare condition in which a fly larva invades the globe, causing iridocyclitis and sometimes subluxation of the lens. Humans are accidental hosts in whom such larvae, after entering the eye, undergo little development. We report a case in which the first larval stage of a rodent or rabbit botfly, Cuterebra sp., invaded the anterior chamber, produced a transient iridocyclitis, and adhered to the posterior cornea where it remained as a dead, slightly atrophic body. Identification of the organism was made by slit-lamp and specular photomicrographs. Tapering doses of topical corticosteroids controlled the inflammation. During 27 months of observation the larva changed only slightly in appearance, the surrounding corneal endothelium remained normal, the cornea remained clear, and the visual acuity remained 20/20.

Adult↗
PubMed1986

Clinical, electron microscopic, and immunohistochemical study of the corneal endothelium and Descemet's membrane in the iridocorneal endothelial syndrome.

Two women with the iridocorneal endothelial syndrome had unilateral corneal edema, iris stromal atrophy, and glaucoma. Each underwent penetrating keratoplasty. Transmission electron microscopy of the corneal buttons disclosed a thin, normally structured Descemet's membrane bounded posteriorly by a posterior collagenous layer that contained banded and fibrillar tissue, indicating that the disorder was acquired after childhood. Scanning electron microscopy showed some degenerated corneal endothelial cells with filopodial cytoplasmic projections, suggesting endothelial migration. Transmission electron microscopy of the endothelium showed no signs of epithelial-like alteration, such as stratification, desmosomal junctions, or increased cytoplasmic fibrils. Immunohistochemical staining of fresh-frozen sections with monoclonal antibodies to keratin showed normal staining of the epithelium and no staining of the endothelium. Occasional lymphocytes were seen within the endothelium in one case but were also observed in one case of an inherited corneal disease, posterior polymorphous dystrophy, suggesting that they might be normal "passenger" cells migrating in the endothelial monolayer.

Adult↗
PubMed1986

Reported satisfaction, fluctuation of vision, and glare among patients one year after surgery in the Prospective Evaluation of Radial Keratotomy (PERK) Study.

We studied satisfaction with the results of radial keratotomy one year after surgery on one eye as reported by 354 patients in the Prospective Evaluation of Radial Keratotomy (PERK) Study. We measured satisfaction using an index based on ten questions that were part of a longer psychometric questionnaire. Patients were generally satisfied with the results of radial keratotomy-48% were very satisfied, 42% were moderately satisfied, and 10% were dissatisfied. A lot of trouble with fluctuating vision was reported by 12% of patients before surgery and by 34% one year after surgery; 17% reported a lot of trouble with glare both before surgery and one year after surgery. The three major factors that influenced satisfaction were uncorrected visual acuity, residual refractive error, and subjective daily fluctuation in vision. A multiple regression equation that incorporated these three variables, glare, and patient sex was able to predict only 46% of the variance in patient satisfaction.

Adult↗
PubMed1986

Late development of ulcerative keratitis in radial keratotomy scars.

We describe three patients in whom ulcerative keratitis developed seven months to 2 1/2 years after uncomplicated radial keratotomy. All ulcers occurred along keratotomy scars within the interpalpebral fissure or inferiorly. At least one case developed spontaneously; another patient may have sustained an unrecognized corneal injury. The third patient was using an extended-wear soft contact lens for correction of residual myopia. Bacteria were isolated from two of the ulcers. With therapy, all ulcers healed without reducing visual acuity. We hypothesize that the altered structure of the slowly healing keratotomy incisions coupled with redistribution of the tear film due to changes in corneal topography may result in intermittent epithelial irregularities. Alone or in conjunction with any form of mechanical or hypoxic corneal injury, these changes along keratotomy incisions may predispose to corneal infection.

Adult↗
PubMed1986

The triple procedure. Analysis of outcome, refraction, and intraocular lens power calculation.

Presented are the results of 66 consecutive, elective, combined procedures of penetrating keratoplasty, extracapsular cataract extraction, and intraocular lens insertion (triple procedure) performed by three surgeons between January 1981 and January 1984. After a mean postoperative followup of 15.8 months, over 90% of the eyes had clear grafts, and of the 56 eyes with good preoperative visual potential, 77% achieved a best corrected visual acuity of 20/40 or better. The postoperative mean refractive deviation from emmetropia was 2.17 diopters, with a range of +6.62 D to -5.50 D, 62% falling between -2.00 and +2.00 diopters. Using multiple regression analysis of preoperative and postoperative variables, an attempt was made to derive a predictive formula for the power of the intraocular lens to be implanted during the triple procedure. In contrast to cataract surgery, where axial length and corneal power remain fairly constant preoperatively and postoperatively, penetrating keratoplasty produces marked changes in corneal curvature and power. Therefore, a single formula could not be derived to predict accurately the intraocular lens power for the patients. However, using the results for an individual surgeon, a formula was derived that could improve the predictability of intraocular lens power.

Aged↗
PubMed1986

Comparison of ultrasonic corneal thickness measurements before and during surgery in the prospective evaluation of Radial Keratotomy (PERK) Study.

Central corneal thickness, determined by an ultrasonic pachymeter, was studied in one eye each of 395 patients enrolled in the Prospective Evaluation of Radial Keratotomy (PERK) Study, to determine the changes in central corneal thickness between preoperative and intraoperative measurements. There was no statistical difference between the preoperative and the intraoperative measurement. However, 9.4% of the corneas were 0.03 to 0.08 mm thinner intraoperatively and 3.3% were 0.03 to 0.06 mm thicker intraoperatively, indicating that clinically meaningful changes in corneal thickness occurred between the preoperative and intraoperative measurements in some eyes. We conclude that the most reliable way to use ultrasonic pachymetry readings to set the length of the knife blade for radial keratotomy surgery is to measure the corneal thickness intraoperatively.

Cornea↗
PubMed1986

Diurnal change in refraction, corneal curvature, visual acuity, and intraocular pressure after radial keratotomy in the PERK Study.

Selected patients who complained of fluctuating visual acuity in the Prospective Evaluation of Radial Keratotomy (PERK) Study were examined before 8:00 a.m. and after 7:00 p.m. on the same day to determine diurnal change in uncorrected visual acuity, best corrected visual acuity, manifest refractive error, average central keratometric power, and intraocular pressure. Sixty-three operated eyes were examined at three months, while 46 operated and 40 unoperated contralateral eyes were examined at one year after radial keratotomy. One year after surgery, 42% of the operated eyes had an increase in minus power of the manifest refraction of 0.50 to 1.25 diopters, 26% of the eyes changed their uncorrected visual acuity by 2 to 4 Snellen lines, and 35% of the operated eyes showed central steepening of the cornea by 0.50 to 1.25 diopters. These changes in the operated eyes at one year were similar to the changes at three months. Minimal diurnal changes occurred in the unoperated eyes at one year. Only 11% of the unoperated eyes changed their manifest refraction by 0.50 to 1.00 diopters, none changed their uncorrected visual acuity by 2 to 4 Snellen lines, and only one of the unoperated eyes changed its central keratometric power by 0.50 diopters. This study documents that many patients who experience diurnal fluctuation of vision have steepening of the cornea and an increase in the minus power of their refraction during the day.

Biomechanical Phenomena↗
PubMed1986

Polysulfone corneal lenses.

Polysulfone is a thermoplastic compound first synthesized in 1965. A unique characteristic of polysulfone is its high refractive index (1.633), which allows very thin optical lenses to be manufactured. Over the last five years, D. Peter Choyce has surgically implanted over 40 polysulfone lenses into eyes of his patients. Analysis of his data indicates that polysulfone intraocular lenses are capable of correcting large refractive errors. Based on his work, a multicenter study was undertaken to evaluate the safety and efficacy of polysulfone as an intracorneal lens material in laboratory models. Four monkeys, eight baboons, and 24 cats were used as laboratory models; 5.0-mm to 6.0-mm diameter hyperopic (+28.5 diopter) and myopic (-17.0 and -25.5 diopter) lenses were surgically implanted within the corneal stroma in one eye of each of the laboratory models while a sham lamellar dissection was performed in the other eye. One hundred percent (4/4) of monkey eyes, 12.5% (1/8) of baboon eyes, and 70.0% (18/24) of cat eyes maintained clear media by ophthalmoscopic examination at follow-ups ranging from three to six months. Complications included both visually and nonvisually significant interface opacities, lens extrusion, anterior corneal necrosis, refractile particles, and epithelial thinning.

Animals↗
PubMed1986

Hydrogel keratophakia: a freehand pocket dissection in the monkey model.

High water content hydrogels can be made with water and solute permeabilities comparable to those of the corneal stroma, thus making them feasible as intrastromal implants for refractive keratoplasty. The materials have been shown to be compatible with the cornea tissue, but for a lenticule of hydrogel to be effective in a refractive keratoplasty procedure it must alter the anterior curvature of the cornea. In this investigation hydrogel lenticules were implanted by a free-hand pocket dissection in eight Macaca mulatta (rhesus) and two Macaca nemestrina (pigtail) primate eyes. The results of pre- and postoperative keratometry and subjective retinoscopy as well as biomicroscopy were recorded. The alteration in refractive power was calculated in relation to the hydrogel lenticule parameters such as base curve, refractive index, etc. The corneal refractive change had a yield of +3 +/- 27% (+/- SD). The central keratometric change had a yield of +6 +/- 16%. The hydrogel plus power lenticule implanted in a free-hand intrastromal pocket created no significant steepening of the anterior cornea surface and therefore little change in refraction.

Animals↗