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Biomedical subjects

G O Waring

Publications and source records attributed to G O Waring.

At least 109 records · Page 6Linked to original sources
PubMed1988

Configuration of corneal trephine opening using five different trephines in human donor eyes.

In this laboratory study, we used five different corneal trephines on 60 fresh human donor eyes with controlled intraocular pressure to study the variation in the size and shape of the trephine openings. With all trephines, the average diameter of the button was larger than the diameter of the trephine at the epithelial side (mean difference, 0.21 mm; range, 0.06 to 0.35 mm) and the endothelial side (mean difference, 0.42 mm; range, 0.13 to 0.79 mm), presumably because the corneal tissue protruded into the trephine during cutting. The trephines that produced the most uniform opening were a nondisposable suction trephine and a freestanding disposable blade, but they caused some undercutting.

Aphakia↗
PubMed1988

Histopathology of traumatic corneal rupture after radial keratotomy.

Two patients (three eyes) had previously undergone technically successful radial keratotomy procedures and subsequently sustained blunt injury to the eyes in motor vehicle accidents one and two years after surgery, respectively, with rupture of the cornea along the keratotomy scars. One case subsequently required penetrating keratoplasty to recover 20/50 visual acuity. The second patient died, but had he survived, the extensive ocular injuries would have required significant surgical and medical care to restore vision. Histologic and ultrastructural studies demonstrated incomplete wound healing in the three corneas. Individuals who have had radial keratotomy, like those who have had penetrating keratoplasty, are at increased risk of corneal rupture after direct ocular trauma.

Accidents, Traffic↗
PubMed1988

Morning-to-evening change in refraction, corneal curvature, and visual acuity 2 to 4 years after radial keratotomy in the PERK Study.

The authors previously reported morning-to-evening changes in ophthalmic measurements at 3 months and at 1-year after radial keratotomy in a self-selected group of patients in the Prospective Evaluation of Radial Keratotomy (PERK) study. Fifty-two patients included in the earlier study were examined again between 2 1/2 and 4 years after surgery before 10:00 AM and after 5:30 PM on the same day to determine if the changes persisted beyond 1 year after surgery. Between the morning and evening examinations, 31% of the eyes had an increase in minus spherical equivalent power of the manifest refraction of 0.50 to 1.50 diopters; 12% had a change in cylinder power of 0.50 to 1.00 D; 19% had a decrease in uncorrected visual acuity of two to five Snellen lines; and 29% showed central corneal steepening by 0.50 to 1.00 D. Thus, in some patients, morning-to-evening fluctuation persisted until 2 1/2 to 4 years after radial keratotomy.

Circadian Rhythm↗
PubMed1988

Late bacterial and fungal keratitis after corneal transplantation. Spectrum of pathogens, graft survival, and visual prognosis.

The authors reviewed 108 bacterial and fungal corneal ulcers that developed 1 to 72 months after penetrating keratoplasty in 79 eyes of 78 patients. Graft hypesthesia, topical corticosteroid and antibiotic treatment, exposed sutures, epithelial defects, and poor visual acuity commonly predated infectious keratitis. There were 69 bacterial, 34 fungal, and 5 combined infections. Candida albicans and Staphylococcus epidermidis were the most common pathogens. Follow-up after infection averaged 23 months (range, 1-80 months). Despite hospitalization and fortified topical antibiotic treatment, complications such as wound dehiscence and corneal perforation necessitated emergency regraft in 38 (35%) cases. Of 73 previously clear grafts, only 29 (40%) retained clarity. Median visual acuity, 20/200 before infection, fell to counting fingers at last follow-up; 12 eyes lost light perception.

Adolescent↗
PubMed1988

Results of anterior segment reconstruction for aphakic and pseudophakic corneal edema.

The authors studied prospectively 59 eyes with corneal edema after cataract surgery that required reconstructive surgery; penetrating keratoplasty in 59 (100%), anterior vitrectomy in 42 (71%), intraocular lens removal or exchange in 33 (56%), gonioplasty in 32 (54%), and iridoplasty in 30 (51%). With an average follow-up of 9.9 months, the corneal transplant was clear in 56 eyes (95%). The corrected visual acuity was improved in 49 eyes (83%) and was the same in seven eyes (12%). Intraocular pressure was less than or equal to 21 mmHg in 47 eyes (80%) and 22 to 29 mmHg in nine eyes (15%). The peripheral anterior synechiae score was the same or improved in 56 eyes (95%). Cystoid macular edema was absent to mild in 52 eyes (88%). Anterior segment reconstruction improved both anatomic integrity and visual acuity of most eyes without increasing complications.

Aged↗
PubMed1988

Effect of donor epithelium on corneal transplant survival.

Two hundred thirty-two penetrating keratoplasties in 228 eyes were performed with or without the removal of donor corneal epithelium in a prospective, randomized clinical trial to determine the effect of epithelial removal on graft survival. The removal of epithelium did not reduce the likelihood of graft failure, irreversible allograft reaction, or reversible allograft reaction.

Corneal Transplantation↗
PubMed1988

Prospective evaluation of radial keratotomy. Photokeratoscope corneal topography.

Preoperative and postoperative corneascope photographs of 368 myopic patients undergoing radial keratotomy in the Prospective Evaluation of Radial Keratotomy (PERK) study were optically scanned and digitized. A high-resolution scanning system was developed in order to quantify the preoperative and postoperative corneal shape accurately. Careful analysis of the 72 data points in the nine representative rings demonstrated that corneal topography is best represented by radius of curvature from the center to the periphery. The normal myopic cornea flattens approximately +0.28 mm from the center to the periphery, demonstrating the cornea's aspheric nature. More highly myopic patients in the PERK population (-4.50 to -8.00 diopters [D]) demonstrated corneas that are 0.08 to 0.10 mm steeper than the less myopic population (-2.00 to -3.12 D). Optical zone, patient age, and gender are all correlated to changes in corneal topography after radial keratotomy. In more myopic populations, men have corneas which are flatter than those of women by 0.09 to 0.11 mm in all rings represented on corneoscopy. Highly myopic males also experience more corneal flattening after 3.0-mm optical zone radial keratotomy. Regardless of the optical zone used in radial keratotomy, the resulting corneal topography flattens in all rings. However, the ratio of millimeters of radius of curvature change to diopters of correction is consistent for each ring. The dioptric change observed after radial keratotomy corresponds closely with the millimeters of flattening at the respective rings being examined. The central rings flatten 0.166-mm radius of curvature per diopter of refractive alteration obtained. The largest degree of corneal flattening occurs centrally, 0.72 mm, in the more highly myopic patients who underwent 3-mm optical zone radial keratotomy. The use of smaller optical zones in radial keratotomy produces larger changes in the radius of curvature and, consequently, in the amount of refraction than when larger optical zones are used. When compared with younger patients, older patients with 3.0, 3.5, and 4.0 optical zone radial keratotomies experience more central and peripheral corneal flattening. This study of the corneal topography of the myopic population demonstrates that the refractive change resulting from radial keratotomy is related to alterations in corneal topography. The use of similar modifications of the corneal surface may be effective for newer refractive surgical procedures.

Adult↗
PubMed1988

The effect of selective suture removal on astigmatism following penetrating keratoplasty.

We retrospectively evaluated selective removal of interrupted nylon sutures to reduce astigmatism following penetrating keratoplasty in 68 eyes with eight or 12 interrupted sutures and one running suture. Following removal of one to four interrupted sutures at one visit (N = 234 visits), corneal astigmatism had changed 2 to 3 diopters (range 0 to 12 D) by the next visit. The astigmatism decreased greater than or equal to 1 D in 54%, changed 0 to .87 D in 28%, and increased greater than or equal to 1 D in 18%. When a total of five or six sutures were removed during the 5 months following surgery, less than 3 D of residual astigmatism was present in 50 eyes (74%). The axis of astigmatism changed less than or equal to 40 degrees in 74% (n = 65). In a second group of 20 eyes with double running sutures, removal of the 10-0 running suture in all 20 eyes produced an average change of 1.8 D (range = 0 to 3.75 D), with an equal number of increases and decreases. Vector analysis showed the total induced change in astigmatism was approximately twice the absolute keratometric change.

Astigmatism↗
PubMed1988

Relationship of glare to uncorrected visual acuity and cycloplegic refraction 1 year after radial keratotomy in the prospective evaluation of radial keratotomy (PERK) study.

This study examines the relationship of subjective glare to refraction and visual acuity, respectively, 1 year after surgery in 435 patients who underwent radial keratotomy for nearsightedness in the Prospective Evaluation of Radial Keratotomy (PERK) study. Patients were asked if they experienced glare in bright light. Of the 425 responding, 200 patients responded "no" and 225 patients responded "yes." We found no statistically significant difference in the mean value of the cycloplegic refraction 1 year after surgery in these two patient groups. (Mean cycloplegic refraction: no = -.48, yes = -.52, p = .73). We also found no difference between these groups with respect to the percent of patients with uncorrected visual acuity of 20/40 or better 1 year after surgery (no = 79%, yes = 76%, p = .46).

Clinical Trials as Topic↗
PubMed1988

Ultrastructural analyses of enzyme-treated microfibrils in rabbit corneal stroma.

Microfibrils have been identified within and between corneal collagen lamellae in a number of vertebrate species in a variety of developmental and pathological conditions, but they are relatively rare in normal adult animals. The present study was undertaken to analyze corneal microfibrils in adult rabbits using enzymatic digestion techniques. Transmission electron microscopy (TEM) showed clusters of 10-15 nm microfibrils arranged in quasi-parallel bundles within or between orthogonally arranged stromal collagen lamellae. When corneas were fixed with tannic acid/glutaraldehyde, the entire stroma showed increased electron density and microfibrillar bundles were heterogeneously stained. Peripheral fibrils were more electron-dense than those located more centrally. Following sequential detergent solubilization of unfixed corneas, all cellular elements were removed and collagen lamellae were distorted. Microfibrillar bundles remained intact, however, and resembled untreated controls. Subsequent treatment with pepsin, trypsin or elastase resulted in swollen corneal tissues in which collagen lamellae were no longer distinguishable but individual collagen fibrils maintained their morphological integrity. In these tissues microfibrillar bundles were rarely identifiable and were reduced to randomly oriented fragments or clusters of filamentous material. Testicular hyaluronidase or chondroitinase ABC did not affect the fibrils. These data indicate that rabbit corneal microfibrils are proteinaceous and that the tannic acid-staining component of the bundles is not glycosaminoglycan. The fibrils are indistinguishable from those identified as oxytalan in cornea and other ocular tissues. Moreover, their sensitivity to elastase and preferential staining with tannic acid/glutaraldehyde strongly suggest they may be related to the elastic system of fibrils.

Animals↗
PubMed1987

Repeated radial keratotomy in the prospective evaluation of radial keratotomy study.

In the Prospective Evaluation of Radial Keratotomy study, 59 patients received a repeated radial keratotomy in which the eight additional incisions were centered between the eight initial incisions. Other aspects of the surgical technique remained the same. The average length of follow-up after the reoperation was 26 months, and ranged from 11 to 42 months. After the reoperation, 45 patients (77%) had a decrease in myopia of 0.50 diopters or more, 12 patients (20%) changed by less than 0.50 diopters, and two patients (3%) had an increase in myopia. Thirty patients (51%) remained undercorrected by more than 1.00 diopter, 27 patients (46%) were between +0.12 and -1.00 diopter, and two patients (3%) were overcorrected by more than 1.00 diopter. There was no relationship between the change in refractive error after the reoperation and any patient characteristics or surgical factors. After the reoperation, the uncorrected visual acuity increased by two to nine Snellen lines for 45 patients (76%), changed one line or less for 13 patients (22%), and decreased three lines for one patient (2%).

Evaluation Studies as Topic↗
PubMed1987

Factors affecting outcome and predictability of radial keratotomy in the PERK Study.

The Prospective Evaluation of Radial Keratotomy (PERK) study used a standardized surgical technique that included a central clear zone with a diameter of 4.0, 3.5, or 3.0 mm. Multiple regression analysis of the outcome in one eye from each of 411 patients disclosed that the diameter of the central clear zone, patient age, and depth of the incision scar were the major factors affecting the change in refraction one year after surgery. Preoperative factors examined that did not have a significant influence on the outcome were sex, average central keratometric power, corneal thickness, corneal diameter, intraocular pressure, and ocular rigidity. The predictability of radial keratotomy, ie, the precision with which the outcome can be estimated, was measured by the 90% confidence interval for the change in refraction based on the regression equation. The width of this interval within each clear zone group was as follows: 4.0 mm, 2.49 diopters; 3.5 mm, 3.38 D; 3.0 mm, 4.12 D. For all 411 eyes, the 90% confidence interval was approximately 3.50 D wide. Thus, the surgeon could be 90% certain that an individual patient's refraction would be within 1.75 D of the predicted value one year after surgery.

Age Factors↗
PubMed1987

Penetrating keratoplasty for pseudophakic corneal edema with exchange of intraocular lenses.

We studied one eye in each of 25 consecutive patients with pseudophakic corneal edema. Each patient underwent a penetrating keratoplasty with exchange of intraocular lenses and was followed up for 12 to 38 months (mean, 18.7 months). The corneal graft remained clear in 22 (88%) eyes, but only eight eyes (32%) had acuity of 20/40 or better; nine eyes (36%) manifested cystoid macular edema, and six eyes (24%) had degenerative maculopathy. Elevated intraocular pressure was present in 12 eyes after surgery, with three eyes manifesting visual field loss; in all eyes the condition was controlled medically. Peripheral anterior synechiae appeared postoperatively in two eyes. We now treat severe cases of pseudophakic corneal edema with a penetrating keratoplasty, meticulous anterior vitrectomy, gonioplasty, iridoplasty, and exchange of intraocular lenses, employing a flexible-loop anterior chamber lens or a posterior chamber lens sutured to the iris.

Adult↗
PubMed1987

Relationship between refractive error and visual acuity in the Prospective Evaluation of Radial Keratotomy (PERK) Study.

As part of the Prospective Evaluation of Radial Keratotomy (PERK) study, we examined the relationship between post-operative refractive error and visual acuity without correction. We included 394 eyes (one eye per patient) with refractive errors ranging from -3.00 to +3.00 diopters one year after radial keratotomy. Within each 1-D range of the spherical equivalent of the refractive error, the visual acuity spanned five to ten Snellen lines. For visual acuities of 20/16 to 20/50, the refractive error spanned 3 to 5 D. Additionally, operated eyes had a better average uncorrected visual acuity than unoperated eyes with a similar refractive error. Within the narrow range of refraction between -2.00 and -2.50 D, the mean uncorrected visual acuity was 20/125 for 56 unoperated eyes and 20/63 for 29 operated eyes, a difference of three Snellen lines.

Adult↗