The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform
J A Venter - One of the best experts on this subject based on the ideXlab platform.
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Photorefractive Keratectomy for Hyperopia after Radial Keratotomy
Journal of Refractive Surgery, 1997Co-Authors: J A VenterAbstract:BACKGROUND Progressive hyperopia is a common complication following Radial Keratotomy. METHODS Ten eyes of ten consecutive patients with hyperopia after Radial Keratotomy between +1.75 and +4.00 diopters (D) were treated with the hyperopia module of the Nidek Model EC-5000 excimer laser. The mean preoperative uncorrected visual acuity was 0.38 (20/60+). RESULTS After excimer laser photorefractive keratectomy (PRK), mean uncorrected visual acuity improved to .72 (20/30+). No complications occurred with the exception of one eye with haze greater than 2+. CONCLUSION PRK for hyperopia is a valuable method for correcting hyperopia after Radial Keratotomy.
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Photorefractive keratectomy for hyperopia after Radial Keratotomy.
Journal of refractive surgery (Thorofare N.J. : 1995), 1997Co-Authors: J A VenterAbstract:Progressive hyperopia is a common complication following Radial Keratotomy. Ten eyes of ten consecutive patients with hyperopia after Radial Keratotomy between +1.75 and +4.00 diopters (D) were treated with the hyperopia module of the Nidek Model EC-5000 excimer laser. The mean preoperative uncorrected visual acuity was 0.38 (20/60+). After excimer laser photorefractive keratectomy (PRK), mean uncorrected visual acuity improved to .72 (20/30+). No complications occurred with the exception of one eye with haze greater than 2+. PRK for hyperopia is a valuable method for correcting hyperopia after Radial Keratotomy.
Thomas H. Mader - One of the best experts on this subject based on the ideXlab platform.
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Refractive Changes at Extreme Altitude After Radial Keratotomy
American journal of ophthalmology, 1995Co-Authors: Thomas H. Mader, Lawrence J. WhiteAbstract:Purpose We studied the effects of altitude on four corneas that had undergone Radial Keratotomy and four normal corneas exposed to increasing elevation during a high-altitude excursion. Methods We measured visual acuity, cycloplegic refraction, keratometry, and intraocular pressure at sea level and after 24-hour exposure to 12,000 and 17,000 ft. Results We observed a significant increase in spherical equivalence (hyperopic shift) in Radial Keratotomy eyes exposed to altitude as compared to controls (P Conclusions Although the specific origin of these changes is open to question, we hypothesize that hypoxic corneal expansion in the area of the Radial Keratotomy incisions may lead to central corneal flattening and a hyperopic shift in refractive error. The cornea that has undergone Radial Keratotomy appears to adjust constantly to changing environmental oxygen concentration, producing a new refractive error over a period of 24 hours or more. Additional study is required to identify with certainty the specific origin of the hyperopic shift at high altitude.
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Penetrating keratoplasty after Radial Keratotomy. A report of six patients.
Ophthalmology, 1995Co-Authors: Vernon C. Parmley, Benny Gee, Walter M. Rotkis, Thomas H. MaderAbstract:Background: For more than 15 years, Radial Keratotomy has increased in popularity as an option for treating myopia in the United States. During this period of time, the procedure has been modified to improve results and decrease complications. Despite these changes, complications from Radial Keratotomy continue to occur. The authors report six cases of penetrating keratoplasty performed to correct significant loss of vision resulting from complications of Radial Keratotomy. Methods: The surgical records of one author (WR) were reviewed retrospectively for penetrating keratoplasties performed for complications of Radial Keratotomy. Results: Six cases of penetrating keratoplasty performed for complications of Radial Keratotomy were found. Severe loss of vision was the indication for surgery in each case, and was associated with aggressive and repeated incisional refractive attempts to correct astigmatism, hyperopic overcorrection, residual myopia, or refractive errors associated with keratoconus. Glare associated with subepithelial scarring and irregular astigmatism were the primary findings associated with loss of vision. Conclusions: Despite advances in technique and instrumentation, Radial Keratotomy is limited in the amount of myopia it can correct. The risk for loss of vision increases with increasing number of incisions, intersecting incisions, very small optical zones, and keratoconus.
Peter J. Mcdonnell - One of the best experts on this subject based on the ideXlab platform.
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Morning-to-evening Change in Refraction, Corneal Curvature, and Visual Acuity 11 Years after Radial Keratotomy in the Prospective Evaluation of Radial Keratotomy Study
Ophthalmology, 1996Co-Authors: Peter J. Mcdonnell, Michael J. Lynn, Azhar Nizam, George O. WaringAbstract:Purpose: Previous reports demonstrate morning-to-evening changes in ophthalmic measurements at 3 months, 1 year, and 4 years after Radial Keratotomy. The authors determine whether diurnal change in refractive error persists 11 years after Radial Keratotomy surgery in the Prospective Evaluation of Radial Keratotomy (PERK) study. Methods: Seventy-one patients were examined in the morning and evening a mean of 11.1 ± 0.6 years (range, 10–12.7 years) after undergoing Radial Keratotomy under a standardized protocol using a diamond blade. Results: Between the morning and evening examinations, the mean change in the spherical equivalent of refraction was a 0.31 ± 0.58-diopter (D) increase in minus power in first eyes. Thirty-six (51%) eyes had an increase in minus power of the manifest refraction of 0.50 to 1.62 D; 22 (31 %) had a change in refractive cylinder power of 0.50 to 1.25 D; 9 (13%) had a decrease in uncorrected visual acuity of two to seven Snellen lines; and 25 (35%) showed central corneal steepening measured by keratometry of 0.50 to 1.94 D. Two (3%) eyes lost two lines of spectacle-corrected visual acuity, whereas one (1%) eye gained two lines. In patients whose both eyes underwent surgery, a high degree of symmetry was observed in morning-to-evening refractive change. Conclusion: In some patients after Radial Keratotomy, morning-to-evening change of refraction and visual acuity persists for at least 11 years, although in most patients the magnitude of this change is small. Thus, diurnal fluctuation may be a permanent sequela of Radial Keratotomy in some individuals.
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Endophthalmitis and Orbital Cellulitis after Radial Keratotomy
Ophthalmology, 1995Co-Authors: Stephen D. Mcleod, Charles W. Flowers, Pedro F. Lopez, Jeffrey L. Marx, Peter J. McdonnellAbstract:Abstract Purpose: To report the findings concerning three patients with endophthalmitis and one with panophthalmitis and orbital cellulitis Radial Keratotomy surgery. Methods: One man referred with panophthalmitis and orbital cellulitis and three women referred with endophthalmitis were treated. Results: After Radial Keratotomy surgery, during which no microperforation or macroperforation had been reported, a severe Pseudomonas panophthalmitis and orbital cellulitis developed in the man. All vision was lost in that eye. Staphylococcus epidermidis endophthalmitis developed in one woman, Streptococcus pneumoniae endophthalmitis in the second woman and Pseudomonas endophthalmitis in the third woman, after undergoing Radial Keratotomy procedures during which microperforations occurred. In the latter patient, bilateral simultaneous surgery was performed, but only one eye became infected. The latter two infections resulted in light perception and hand motion vision respectively. In three cases, an initial keratitis was located in the inferior cornea. Conclusions: Severe bacterial endophthalmitis can occur after Radial Keratotomy surgery, even in the absence of microperforation during the procedure. Any evidence of postoperative keratitis must be regarded seriously and treated aggressively. Despite use of this approach, the effect on final visual acuity can be devastating.
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Diurnal Variation of Corneal Topography After Radial Keratotomy
Archives of ophthalmology (Chicago Ill. : 1960), 1992Co-Authors: Sérgio Kwitko, Jenny J. Garbus, David C. Gritz, W. James Gauderman, Peter J. McdonnellAbstract:• A computerized videokeratography system was used to evaluate diurnal changes in corneal curvature of both untreated and surgically treated eyes of 11 patients who had undergone unilateral Radial Keratotomy. The mean postoperative interval was 34.5 months. Both corneas operated on and those not operated on steepened on average from morning to evening. For untreated eyes, this diurnal steepening was statistically significant at a distance of 0.5 mm from the corneal apex (mean±SE, 0.36±0.07 diopter) and in the inferotemporal quadrant (0.28±0.08 D); in eyes that had undergone Radial Keratotomy, steepening was significant at from 1.0 to 3.0 mm from the corneal apex (0.39±0.07 D) and temporal, inferotemporal, inferior, inferonasal, nasal, and superonasal to the corneal apex (0.42±0.08 D). The greatest steepening in the eyes treated with Radial Keratotomy compared with the untreated eyes occurred at 1.5 to 2.5 mm peripheral to the corneal apex in the inferonasal and nasal octants. Diurnal changes in intraocular pressure, corneal thickness, number of incisions, clear-zone size, postoperative period, and patient sex were not predictive of the magnitude of morning-to-evening change. Furthermore, diurnal changes in corneal curvature of untreated eyes were not predictive of diurnal changes in the fellow eyes after Radial Keratotomy.
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Pharmacologic alteration of corneal topography after Radial Keratotomy.
Ophthalmic surgery, 1992Co-Authors: Sérgio Kwitko, Abdelhamid Sinbawy, Martha Lee, Peter J. McdonnellAbstract:Contraction of corneal wounds as the incisions heal may account for changes in corneal topography after Radial Keratotomy; such contractility of avascular corneal wounds has been demonstrated in vitro. Using a cat model of Radial Keratotomy, we demonstrated in vivo contractility of Radial Keratotomy incisions. In eight eyes of adult female cats, four-incision Radial keratotomies were performed, producing central corneal flattening. After 3 and 8 days, serotonin (1 mg/mL) was applied. On day 3, application of topical serotonin resulted in corneal steepening (P < .0001); serotonin produced no topographic changes when applied on day 8 and had no effect on normal unoperated corneas. Vehicle produced no change in corneal curvature before or at any time after Radial Keratotomy. Fluorescence microscopy revealed cells with myofibroblastic differentiation at the incisions. These data suggest that cells with contractile abilities play a role in determining corneal topography after Radial Keratotomy.
George O. Waring - One of the best experts on this subject based on the ideXlab platform.
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Morning-to-evening Change in Refraction, Corneal Curvature, and Visual Acuity 11 Years after Radial Keratotomy in the Prospective Evaluation of Radial Keratotomy Study
Ophthalmology, 1996Co-Authors: Peter J. Mcdonnell, Michael J. Lynn, Azhar Nizam, George O. WaringAbstract:Purpose: Previous reports demonstrate morning-to-evening changes in ophthalmic measurements at 3 months, 1 year, and 4 years after Radial Keratotomy. The authors determine whether diurnal change in refractive error persists 11 years after Radial Keratotomy surgery in the Prospective Evaluation of Radial Keratotomy (PERK) study. Methods: Seventy-one patients were examined in the morning and evening a mean of 11.1 ± 0.6 years (range, 10–12.7 years) after undergoing Radial Keratotomy under a standardized protocol using a diamond blade. Results: Between the morning and evening examinations, the mean change in the spherical equivalent of refraction was a 0.31 ± 0.58-diopter (D) increase in minus power in first eyes. Thirty-six (51%) eyes had an increase in minus power of the manifest refraction of 0.50 to 1.62 D; 22 (31 %) had a change in refractive cylinder power of 0.50 to 1.25 D; 9 (13%) had a decrease in uncorrected visual acuity of two to seven Snellen lines; and 25 (35%) showed central corneal steepening measured by keratometry of 0.50 to 1.94 D. Two (3%) eyes lost two lines of spectacle-corrected visual acuity, whereas one (1%) eye gained two lines. In patients whose both eyes underwent surgery, a high degree of symmetry was observed in morning-to-evening refractive change. Conclusion: In some patients after Radial Keratotomy, morning-to-evening change of refraction and visual acuity persists for at least 11 years, although in most patients the magnitude of this change is small. Thus, diurnal fluctuation may be a permanent sequela of Radial Keratotomy in some individuals.
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Radial Keratotomy Does Not Affect Intraocular Pressure
Refractive & corneal surgery, 1993Co-Authors: Srinivas M. Sastry, Robert D. Sperduto, George O. Waring, Nancy A. Remaley, Michael J. Lynn, Ernesto E. Blanco, David N MillerAbstract:BACKGROUND Recent reports have suggested that a secondary effect of Radial Keratotomy may be a reduction in intraocular pressure (IOP) levels. METHODS In an effort to study the relationship of Radial Keratotomy to IOP, we compared the mean IOP from the baseline and follow-up visits during 1 year after surgery of operated versus nonoperated eyes of patients enrolled in the Prospective Evaluation of Radial Keratotomy (PERK) study. To investigate if Radial Keratotomy had more of an effect on eyes with higher baseline IOPs, the same analysis was performed on a subset (134 patients) who had a baseline IOP of 15 mm Hg or greater. RESULTS The average baseline IOP for both operated eyes and nonoperated eyes was 14.6 mm Hg. There was no significant difference in mean IOP between operated and nonoperated eyes across all time points (p = .18). Although mean IOP changed over time, it did not clinically differ in operated versus nonoperated eyes at any time point. These findings were similar in the analysis of eyes with higher baseline IOP (15 mm Hg or greater). CONCLUSION We conclude that the Radial Keratotomy performed in the PERK study had no effect on IOP within 1 year after surgery.
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Computer-assisted videokeratography of corneal topography after Radial Keratotomy.
Archives of ophthalmology (Chicago Ill. : 1960), 1991Co-Authors: Stephen J. Bogan, Robert K. Maloney, Carolyn Drews, George O. WaringAbstract:We used computer-assisted videokeratography to compare the topographies of 32 corneas from 23 subjects after Radial Keratotomy with those of 47 normal corneas from 47 subjects controlled for age and preoperative keratometric and refractive power. Three ophthalmologists independently classified color-coded videokeratographs based on the color-coded pattern of dioptric power distribution and the cross-sectional shape. Corneas that had Radial Keratotomy exhibited a polygonal pattern not seen in normal eyes; this occurred in 59% of corneas. All normal corneas demonstrated a cross-sectional shape configuration that was steeper centrally than peripherally; 79% of corneas after Radial Keratotomy had a shape that was flatter centrally than peripherally. After Radial Keratotomy, the dioptric power increased from the center to the periphery (radius of approximately 4.6 mm) by 2.8 +/- 2.2 diopters (mean +/- SD), with a sharp inflection zone ("paracentral knee") 2.7 mm from the center; normal corneas showed a smooth decrease in power from the center to the periphery of 1.9 +/- 0.5 diopters.
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The relationship of visual acuity, refractive error, and pupil size after Radial Keratotomy.
Archives of ophthalmology (Chicago Ill. : 1960), 1991Co-Authors: Jack T. Holladay, George O. Waring, Michael J. Lynn, Mary C. Gemmill, Gordon C. Keehn, Brooke FieldingAbstract:To better define the relationship between residual refractive error, uncorrected visual acuity, and pupil diameter, we compared 42 eyes that had an eight-incision Radial Keratotomy according to the Prospective Evaluation of Radial Keratotomy Study protocol with 42 matched control eyes. The parameters measured were best corrected visual acuity, uncorrected visual acuity, and the change in cycloplegic refraction with enlarging pupil diameter. The best corrected visual acuity was 20/16 in both the Radial Keratotomy and control groups, but the variability (SD) was higher in the Radial Keratotomy group. The average uncorrected visual acuity was 0.35 (35%) better in the Radial Keratotomy group, but the variability was 1.77 times higher. Change in refraction with dilation occurred in 9% of the controls and 36% of the Radial Keratotomy patients, indicating a significant difference (P = .002). The change in refraction with dilation in the eyes with Radial Keratotomy was almost equally split between a hyperopic change (17%) and a myopic change (18%), which was much different than in the control eyes, only 2% of which changed in a hyperopic direction and 7% in a myopic direction. The Radial Keratotomy patients with a myopic change had the best uncorrected visual acuity, indicating that positive spherical aberration yielded the best aspherical surface for uncorrected visual acuity.
Gie Woo - One of the best experts on this subject based on the ideXlab platform.
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Excimer photorefractive keratectomy after undercorrected Radial Keratotomy.
Journal of Refractive Surgery, 1995Co-Authors: Marvin L Kwitko, James A Gow, François Bellavance, Gie WooAbstract:Radial Keratotomy has been used for the treatment of myopia since 1979. Until recently, patients with undercorrected myopia had recourse only to repeated Keratotomy. Now patients undercorrected after two or more Radial Keratotomy procedures can be treated with the excimer laser to reduce the residual myopia. Nineteen eyes of 17 patients with undercorrected myopia after repeated Radial had excimer photoRadial keratectomy performed. The mean residual spherical equivalent refractive error after Radial Keratotomy was -2.74 +/- 1.06 diopters (D). This was further reduced after PRK. Final uncorrected visual acuity ranged from 20/20 to 20/70. Excimer laser PRK offers a safe and more controlled method of treating residual after Radial Keratotomy.
