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Biomedical subjects

G O Waring

Publications and source records attributed to G O Waring.

At least 55 records · Page 3Linked to original sources
PubMed1994

Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery.

OBJECTIVE: To determine the long-term effects and stability of refraction following a standardized technique of radial keratotomy for myopia in the nine-center Prospective Evaluation of Radial Keratotomy (PERK) Study 10 years after surgery. METHODS: Radial keratotomy using eight centripetal incisions was performed to reduce myopia of -2.00 to -8.75 diopters in 1982 and 1983. A mean of 10 years later, patients underwent a standardized ophthalmic examination similar to previous study examinations. RESULTS: Of 427 patients (793 eyes that underwent radial keratotomy), 374 patients (88%) (693 eyes) returned for the 10-year examination. Of 675 eyes with refractive data, 38% had a refractive error within 0.50 D and 60% within 1.00 D. For 310 first-operated eyes, the mean refractive error was -0.36 D at 6 months and changed in a hyperopic direction to + 0.51 D at 10 years. The average rate of change was +0.21 D/y between 6 months and 2 years and +0.06 D/y between 2 and 10 years. Between 6 months and 10 years, the refractive error of 43% of eyes changed in the hyperopic direction by 1.00 D or more. The hyperopic shift was statistically associated with the diameter of the clear zone. Uncorrected visual acuity was 20/20 or better in 53% of 681 eyes and 20/40 or better in 85%. Loss of spectacle-corrected visual acuity of 2 lines or more on a Snellen chart occurred in 3% of all 793 eyes that underwent surgery. Among 310 patients with bilateral radial keratotomy, 70% reported not wearing spectacles or contact lenses for distance vision at 10 years. CONCLUSION: The PERK technique of radial keratotomy eliminated distance optical correction in 70% of patients, with a reasonable level of safety. A shift of the refractive error in the hyperopic direction continued during the entire 10 years after surgery.

Adult↗
PubMed1994

Penetrating keratoplasty with anterior or posterior chamber intraocular lens implantation.

OBJECTIVE: To compare the outcome of anterior chamber (AC) intraocular lens (IOL) implantation with the outcome of posterior chamber (PC) IOL implantation at the time of penetrating keratoplasty in the absence of capsular support. DESIGN: Retrospective study of 122 eyes that underwent secondary IOL implantation without capsular support at the time of penetrating keratoplasty. Ninety eyes received an AC IOL and 32 received a PC IOL sutured to the iris or the ciliary sulcus. RESULTS: Survival analysis showed the probability of a clear graft to be 86% for eyes with an AC IOL and 90% for eyes with a PC IOL at 1 year. Intraocular pressure rose by 5 mm Hg or more in 30% of eyes with AC IOLs and 5% of eyes with PC IOLs. Visual acuity was better than 20/200 in 48% of eyes with AC IOLs and 68% of eyes with PC IOLs. CONCLUSION: This study demonstrated a trend for a better outcome with PC IOLs than AC IOLs for secondary implantation at time of penetrating keratoplasty in the absence of capsular support.

Adult↗
PubMed1994

Spectacle and contact lens wearing six years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study.

BACKGROUND: Patients in the Prospective Evaluation of Radial Keratotomy (PERK) Study stated that a major reason for obtaining radial keratotomy was to see without dependence on corrective lenses. The authors examined lens-wearing patterns 6 years after surgery. METHODS: Of the 435 patients in the PERK Study, the authors analyzed the responses of 328 (75.4%) who elected to have surgery on both eyes, who completed a questionnaire at 6 years, and for whom visual acuity and cycloplegic refraction were available. RESULTS: Sixty-four percent (106/167) of patients younger than 40 years of age and 38% (64/161) of patients older than 40 years of age wore no lenses for distance or near vision. The proportion of time lenses were worn increased with age for those who wore them for close work only (from 18% younger than 40 years of age to 25% older than 40 years of age) and decreased with age for those who wore them for distance only (from 41% to 27%). The authors examined the visual acuity and refractive error criteria for patients to be free of distance lenses. Of the 359 patients who saw 20/20 or better uncorrected in one or both eyes, 77% (n = 198) wore no distance correction, whereas of the 53 patients who saw 20/25 to 20/40 in both eyes or their best eye, only 34% (n = 18) wore no distance correction. Of the 72 patients with a residual refractive error of +/- 0.50 diopters (D) in both eyes, 85% (n = 61) wore no distance correction, whereas of the 87 patients with +/- 1.00 D in both eyes, only 39% (n = 34) wore no distance correction. Of the 328 patients, 60% (n = 197) were highly satisfied with the results of surgery, and satisfaction was primarily predicted by having a visual acuity 20/20 or better in at least one eye and not wearing spectacles for distance vision. Before surgery, 57% of patients reported worrying about their eyesight and 47% reported restrictions in activities because of their eyes; these rates dropped to 31% and 9%, respectively, at 6 years. Of the 328 patients, 74% (n = 243) said their preoperative goals were completely met and 94% (n = 308) said they would have radial keratotomy again. CONCLUSION: The use of 20/40 uncorrected visual acuity and a residual refractive error of +/- 1.00 D were insensitive criteria for evaluating distance spectacle independence. The ability to function without lenses increased substantially only when patients had an uncorrected visual acuity of 20/20 or better in at least one eye, and a refractive error within +/- 0.50 D.

Adult↗
PubMed1994

Corneal opacities in spondyloepiphyseal dysplasia tarda.

Spondyloepiphyseal dysplasia tarda is an inherited skeletal dysplasia involving the spine and epiphyses of long bones with onset in childhood, giving rise to disproportionate short stature and degenerative spine and hip disease. Associated ocular disease is not commonly recognized. We report a patient with spondyloepiphyseal dysplasia tarda and a unique pattern of corneal opacities. Bilateral, irregularly shaped, nodular, deeply posterior opacities confined to the peripheral cornea were noted in this patient. A central stromal granularity was also seen. Minimal visual loss was associated with these findings. An X-linked inheritance pattern is presumed but could not be confirmed.

Aged↗
PubMed1993

Bacterial and fungal endophthalmitis after penetrating keratoplasty.

We analyzed 1,010 consecutive penetrating keratoplasties to determine the incidence of postoperative endophthalmitis, the frequency of positive donor rim cultures, and whether a correlation between these two factors exists. There were three cases of bacterial endophthalmitis, all caused by streptococci, and one case of Candida albicans endophthalmitis. In all cases except one case of streptococcal endophthalmitis, the same organism was cultured from the donor rim. We cultured 138 organisms from 128 of 932 donor rims (14%). A remarkable percentage of gram-positive organisms were resistant to gentamicin, the only antibiotic contained in corneal storage media. On the basis of our data and previously published data, we believe that donor material is frequently the source of microorganisms in endophthalmitis after penetrating keratoplasty.

Adult↗
PubMed1993

Comparison of laser phacovaporization using the Er-YAG and the Er-YSGG laser.

OBJECTIVE: To study the interaction of the erbium (Er)-YAG (2.94 microns) and the Er-YSGG (2.79 microns) lasers with the human crystalline lens tissue. METHODS: Fresh human crystalline lens sections were used to measure the photovaporization threshold, rate, and damage zone of the two lasers. RESULTS: We found the photovaporization threshold for the Er-YAG and the Er-YSGG lasers to be 1.4 J/cm2 and 5.5 J/cm2, respectively. At 10 J/cm2, the photovaporization rate is 67.9 microns per pulse for the Er-YAG laser and 18.4 microns per pulse for the Er-YSGG laser. The increased rate of photovaporization as a function of radiant energy for the Er-YAG laser is almost twice that for the Er-YSGG. Damage zones for the Er-YAG laser ranged from 4 to 9 microns compared with 10 to 22 microns for the Er-YSGG. CONCLUSIONS: It is apparent that both lasers can adequately photovaporize human crystalline lens tissue and should be further studied for this purpose.

Cataract Extraction↗
PubMed1993

Keratotomy for astigmatism using an arcuate keratome.

We describe a new system for performing transverse arcuate corneal incisions for the correction of astigmatism. The instrument consists of a conical housing with suction and/or friction fixation to the limbus and two micrometric diamond knives mounted on a carrier that can be rotated by a gear mechanism. The depth, length, and location of the incisions can be predetermined. Light microscopy of donor eye corneas documented the achieved incision depth. One sweep at normal speed produced an incision depth 28% less deep than the preset depth. One sweep at low speed achieved depths of approximately 100% of the knife setting. Variability from one incision to another in the same cornea was related to blade sharpness. We report successful use of the instrument in five consecutive eyes with naturally occurring astigmatism.

Adolescent↗
PubMed1993

Determination of corneal image-forming properties from corneal topography.

Keratometry provides useful information about the cornea's image-forming properties, such as corneal astigmatism, but is inaccurate on irregular corneas. Quantitative corneal topographic information is now obtainable on irregular corneas, but is difficult for the clinician to interpret. We developed a method to determine the spherical power, astigmatism, and topographic irregularity of a cornea by finding the best-fit spherocylinder that was closest to its measured topography. Keratometric measurements and two videokeratographs were gathered prospectively on 262 normal and abnormal corneas. The best-fit measurements of spherical power, astigmatism, and topographic irregularity were reproducible with one standard deviation of 0.75 diopter or better; agreement with keratometric measurements in normal eyes was good (0.60 diopter or better). Topographic irregularity averaged 0.1 diopter on precision spheres, 0.4 diopter on 146 normal eyes, 0.8 diopter on 29 eyes after radial keratotomy, 2.0 diopters on 58 eyes after penetrating keratoplasty, and 3.0 diopters on 29 eyes with advanced keratoconus. We conclude the following: basic corneal image-forming properties can be measured from videokeratographs; the properties can be determined, by our methods, on irregular corneas in which keratometry is unreliable; and topographic irregularity provides a measure of irregular astigmatism.

Astigmatism↗
PubMed1993

A randomized trial of intraocular lens fixation techniques with penetrating keratoplasty.

PURPOSE: Pseudophakic corneal edema is the principal indication for penetrating keratoplasty in the United States. Currently, three techniques of intraocular lens (IOL) fixation during penetrating keratoplasty for this condition are commonly used--flexible anterior chamber IOL (AC IOL) implantation, iris suture fixation of a posterior chamber IOL (PC IOL), and transscleral suture fixation of a PC IOL. This study represents the first prospective, randomized comparison of these three techniques. METHODS: One hundred seventy-six consecutive patients with pseudophakic corneal edema who underwent penetrating keratoplasty with IOL exchange were randomized to one of the three implantation techniques. Standardized evaluations were performed at baseline and at 6, 12, and 18 months postoperatively. Life-table analysis provided cumulative risk estimates for specific complications. RESULTS: Randomization produced comparable groups at baseline. The cumulative risk of macular edema was significantly less for the iris fixation cohort than for either the AC IOL or scleral fixation group. A complications index was constructed based on the major adverse outcomes of glaucoma escalation, cystoid macular edema, IOL dislocation, and graft failure. A significantly lower risk of complication was found for iris compared with scleral fixation of PC IOLs. CONCLUSION: The authors conclude that transscleral fixation of the PC IOL at the time of penetrating keratoplasty for pseudophakic corneal edema is associated with a greater risk of adverse outcome than iris fixation of a PC IOL.

Aged↗
PubMed1993

A prototype erodible mask delivery system for the excimer laser.

PURPOSE: The authors developed an erodible mask delivery system for the argon-fluoride 193-nm excimer laser, which offers the possibility of correcting hyperopia and astigmatism as well as myopia. METHOD: Masks were made of polymethylmethacrylate on a quartz window, with intended corrections for myopia and hyperopia of 2.5 and 5 diopters (D). Ablations using the mask and control ablations using an expanding diaphragm were performed in 30 eyes of 15 pigmented rabbits with an Excimed UV200 laser (Summit Technology, Inc, Waltham, MA). The rabbits were followed for 134 days with regular biomicroscopy and retinoscopic examination by two observers. RESULTS: Ablations with the mask to correct myopia were successful and produced stable corrections, although the higher-power mask produced undercorrections. Hyperopic masks produced paradoxic myopic corrections, possibly due to the lack of a transition zone at the edge of the mask. Corneas ablated with the mask had less sub-epithelial haze than those ablated with the diaphragm at all examinations. Results of histopathologic examination showed epithelial hyperplasia over the ablation zone in all eyes. Dichlorotriazinyl aminofluorescein collagen staining showed subepithelial new collagen in all eyes, but there was no relation between the depth of ablation at any point on the cornea and the amount of new collagen deposited there. CONCLUSIONS: Myopic ablations are feasible with the erodible mask, although additional calibration is needed. Hyperopic ablations were unsuccessful with the current design. Corneas ablated with the mask may be clearer than corneas ablated with the diaphragm, possibly due to a smoother ablated surface. Regression of effect after laser ablation in the rabbit model is likely due more to epithelial hyperplasia than to stromal remodeling.

Animals↗
PubMed1993

Changes in keratometric astigmatism after suture removal more than one year after penetrating keratoplasty.

BACKGROUND/PURPOSE: Selective removal of interrupted sutures and adjustment of a running suture can minimize astigmatism after penetrating keratoplasty, but the long-term effects of early suture manipulations remain largely unknown. The authors tested the hypothesis that the cornea becomes "fixed" more than 1 year after keratoplasty so that desirable refractive results will remain when all sutures are eventually removed. METHODS: The authors reviewed retrospectively the changes in astigmatism that occurred when all remaining sutures were removed from 162 eyes 1 to 6 years after penetrating keratoplasty. Single-running sutures were used in 130 eyes, double-running sutures in 20 eyes, and a combination of interrupted and running sutures in 12 eyes. RESULTS: Removal of single-running sutures caused an average decrease in astigmatism of 0.52 diopters (D) from 6.10 +/- 4.41 D to 5.57 +/- 3.14 D. However, the astigmatism in 62% of eyes changed 2 or more D (range, 11.94 to -17.87 D), and the range changed more than 20 degrees in 55% of eyes. The average vectorial change was 6.5 +/- 4.3 D (range, 0.59 to 19.8 D). There was no decrease in the amount of astigmatic change with increasing time between surgery and suture removal. Graft size and diagnosis had no effect on the amount of astigmatic change. Astigmatic errors became stable, with less than 1 D of change between successive examinations within 6 months after suture removal. Similar results were obtained for eyes with double-running and interrupted-running sutures. CONCLUSIONS: Corneal astigmatism may change unpredictably and by large amounts when all remaining sutures are removed 1 to 6 years after penetrating keratoplasty.

Astigmatism↗
PubMed1993

Synthetic epikeratoplasty in rhesus monkeys with human type IV collagen.

Human type IV collagen discs were found to support proliferation and adhesion of rabbit corneal epithelial cells in tissue culture. To assess the biocompatibility of this synthetic collagen for epikeratoplasty, seven eyes of seven rhesus monkeys underwent epikeratoplasty with lenticules made of human type IV collagen. Eye rubbing by the animals expulsed two of the lenticules and caused failure of two to epithelialize completely. The remaining three lenticules epithelialized, remained clear, and caused no adverse effects on the eye. Two of these lenticules developed focal areas of subepithelial thinning 3 months postoperatively and the third lenticule has remained stable for 30 months. The presence of epithelial attachment components at the epithelial-lenticule interface was demonstrated by immunolocalization. Histopathologic and ultrastructural examination revealed focal areas of epithelial invasion and degradation of the lenticule. Neutral proteases were detected in the thinning region of one specimen. Human type IV collagen supports epithelialization in vivo and may have potential as a biomaterial for epikeratoplasty, but the stability of the material must be improved.

Animals↗
PubMed1992

Subepithelial fibrosis after myopic epikeratoplasty. Report of a case.

A 29-year-old man with a -22.00-diopter myopia in the right eye underwent a planar, nonfreeze myopic epikeratoplasty and postoperatively developed a central subepithelial opacity. The opacity recurred after two superficial keratectomies; finally, another epikeratoplasty was performed. Light microscopic examination of the original button showed that the epithelium was thickened, collagenous subepithelial fibrocellular tissue was present, and Bowman's layer was focally disrupted. The stroma was edematous and peripherally scarred with scattered keratocytes. Examination by transmission electron microscopy revealed keratocytes lying anterior and posterior to Bowman's layer. The subepithelial fibrocellular tissue corresponded to an area of a break in Bowman's layer and probably originated from the donor stroma. The break in Bowman's layer may have been caused by the microkeratome cuts, but its origin is not certain.

Adult↗
PubMed1992

Corneal wound healing in monkeys after repeated excimer laser photorefractive keratectomy.

Five rhesus monkey eyes underwent repeated argon fluoride (193 nm) excimer laser myopic photorefractive keratectomy 3 months following an initial ablation that had produced mild subepithelial haze. At 3 months all eyes had development of a dense subepithelial opacity and a thickened epithelium (12 cells, 80 microns) with vacuolization of basal cells, fragmented basement membrane, and a layer of subepithelial fibrosis containing activated fibroblasts. By 6 months the opacity was clearing; epithelium was thinner (50 microns); subepithelial fibrosis was more lamellar. By 15 months only mild haze persisted clinically; epithelium was 30 microns thick, with persistent basal vacuolization and focal basement membrane disruption; subepithelial fibrous tissue was more organized. Early repeated excimer laser ablation of the monkey cornea apparently induces vigorous stromal wound healing. Use of shallower ablations, corticosteroids, or a longer delay between ablations may be necessary for repeated laser surgery to be practical clinically.

Animals↗