Prospective Evaluation Of Radial Keratotomy Research Articles

Berberine (BBR) Attenuated Palmitic Acid (PA)-Induced Lipotoxicity in Human HK-2 Cells by Promoting Peroxisome Proliferator-Activated Receptor α (PPAR-α).

BackgroundBerberine (BBR), a natural alkaloid isolated from Coptis chinensis, has frequently been reported as an antidiabetic reagent, partly due to its lipid-lowering activity. Evidence suggests that BBR ameliorates palmitate-induced lipid deposition and apoptosis in renal tubular epithelial cells (TECs), which tracks in tandem with the enhancement of peroxisome proliferator-activated receptor a (PPAR-a). The study aim was to investigate the roles of BBR in renal lipotoxicity in vitro, and investigate whether PPAR-a was the underlying mechanism.Material/MethodsHuman TECs (HK-2 cells) were injured with palmitic acid (PA), and then treated with BBR, BBR+PPAR-a inhibitor (GW6471), and PA+PPAR-a agonist (fenofibrate). Endoplasmic reticulum (ER) stress was assessed by measuring the expression of prospective evaluation of radial keratotomy (PERK), C/EBP-homologous protein (CHOP), and 78 kDa glucose-regulated protein (GRP78). Lipid metabolism was assessed by determining lipid anabolism-associated genes, including fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), and lipoprotein lipase (LPL), as well as lipid catabolism-associated gene, including carnitine palmitoyl transferase 1 (CPT1). Inflammatory response of HK-2 cells was evaluated by measuring interleukin (IL)-6 and tumor necrosis factor (TNF)-a. Cell apoptosis and protein levels of cleaved-caspase-3 were evaluated.ResultsPA downregulated PPAR-a and induced server lipotoxicity in HK-2 cells by ER stress, increasing lipid deposition, and elevating inflammatory response of HK-2 cells accompanied with inducting cell apoptosis and cleaved-caspase-3, which were obviously reversed by additional treatment of BBR or PPAR-a agonist. However, the protective effect of BBR in PA-induced lipotoxicity in HK-2 cells was significantly ameliorated by PPAR-a inhibitor.ConclusionsBBR attenuated PA-induced lipotoxicity via the PPAR-a pathway.

The use of contact lenses after refractive surgery

No abstract available

Making Sense of Refractive Surgery in 2001: Why, When, for Whom, and by Whom?

Making Sense of Refractive Surgery in 2001: Why, When, for Whom, and by Whom?

Functional outcome and satisfaction after photorefractive keratectomy : Part 1: development and validation of a survey questionnaire

Objective The aim of this study was to develop a valid, reliable, and easy-to-administer instrument to assess patient satisfaction and perceived outcome after bilateral excimer laser photorefractive keratectomy. Design Development and validation of a psychometric questionnaire. Participants Consecutive patients who underwent bilateral excimer laser photorefractive keratectomy from May 1994 through May 1997 by 12 surgeons from four collaborating centers. To be eligible, a minimum of 4 months since the last surgery and a maximum of 30 months since the first surgery was required. Methods The new instrument was derived in part from the Prospective Evaluation of Radial Keratotomy (PERK) study 10-year psychometric questionnaire and the Visual Functional Index (VF-14), an index of functional impairment in patients with cataract. Questions were grouped in seven scales, each covering a specific aspect of quality of vision. These included global satisfaction, quality of uncorrected vision, quality of corrected vision, quality of night vision, glare, daytime driving, and night driving. Main outcome measures Acceptability, reliability, validity, and interpretability of the instrument, as well as its ease of administration. Results The instrument scale structure was examined and scale scores were created. Item-discriminant validity ensured that questions belonged to their hypothesized scale, based on multitrait correlation analysis. The instrument was shown to be reliable by a high level of internal consistency, and all Cronbach’s α coefficients were superior or equal to 0.83. Construct-related validity and interpretability were assessed based on correlations between scale scores and clinically recognized success criteria such as visual acuity and refraction. Respondent burden was shown to be minimal. Acceptability of the instrument was shown to be very good, with a participation rate of 74.3% (690 of 929 patients). The instrument is available in English and in French and the translation was shown to be reliable. Conclusions The acceptability, reliability, and interpretability of the instrument, as well as its ease of administration, were shown to be adequate. This questionnaire appears clinically useful to document patient satisfaction after excimer laser photorefractive keratectomy.

Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the prospective evaluation of radial keratotomy study

Purpose To correlate clinically observed fluctuations in manifest refraction, visual acuity, keratometry, and intraocular pressure (IOP) with changes in the anterior corneal surface as measured by videokeratography in patients 10 years after radial keratotomy (RK). Setting Four clinical centers in the United States that participated in the Prospective Evaluation of Radial Keratotomy (PERK) study. Methods Thirty-two eyes of 20 PERK patients who noted diurnal fluctuations in vision had clinical examination and videokeratography (TMS-1, Computed Anatomy Inc.) in the morning and evening of the same day a mean of 10.3 years (range 7.8 to 11.7 years) after RK. The videokeratographs were analyzed in terms of various indexes generated by custom-designed software. Morning-to-evening changes in the means of the various clinical and videokeratographic values were assessed using pairwise methods. Results The mean increase in myopia was 0.36 diopters (D) ± 0.58 (SD) from morning to evening ( P < .01). Analysis of the videokeratographs showed a corresponding increase in average corneal power (ACP), reflecting a steepening of 0.52 ± 0.45 D ( P < .001). The change in ACP was correlated with a change in the manifest spherical equivalent refraction ( R = 0.39, P = .03) and a change in best spectacle-corrected visual acuity ( R = 0.38, P = .03) over the same period. Similarly, simulated keratometry (SimK) readings correlated with the change in the manifest spherical equivalent refraction ( R = 0.38, P = .03 for SimK1; R = 0.37, P = .35 for SimK2; R = 0.4, P = .02 for average SimK), although the standard clinical keratometric data did not ( P = .26 for K1, P = .11 for K2, and P = .09 for the mean K). The elevation depression magnitude, a measure of the low-frequency irregularities of the cornea, showed a decrease of 0.32 ± 1.59, which also correlated with the change in the manifest spherical equivalent refraction ( R = 0.37, P = .04). Intraocular pressure tended to decrease from morning to evening (mean change of −0.97 ± 3.29 mm Hg), but the difference was not significant. Variations in IOP in individual patients, however, were correlated with changes in the manifest spherical equivalent refraction ( R = 0.37, P = .04). Conclusions Diurnal fluctuations in corneal topographic indexes can be used to evaluate the diurnal fluctuations in refraction and visual acuity after RK. The study findings provide statistical support for the idea that IOP contributes to the diurnal fluctuation in visual acuity after RK.

Morning-to-evening Change in Refraction, Corneal Curvature, and Visual Acuity 11 Years after Radial Keratotomy in the Prospective Evaluation of Radial Keratotomy Study

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. 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. 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. 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.

Spectacle and Contact Lens Wearing Six Years after Radial Keratotomy in the Prospective Evaluation of Radial Keratotomy Study

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. 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. 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. 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.

Radial Keratotomy Does Not Affect Intraocular Pressure

Recent reports have suggested that a secondary effect of radial keratotomy may be a reduction in intraocular pressure (IOP) levels. 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. 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). We conclude that the radial keratotomy performed in the PERK study had no effect on IOP within 1 year after surgery.

The Casebeer System for Predictable Keratorefractilove Surgery: One-year Evaluation of 205 Consecutive Eyes

This study documents the results of current radial keratotomy (RK) surgical technology, using the Casebeer keratorefractive system. These results are contrasted to those of the Prospective Evaluation of Radial Keratotomy (PERK) keratorefractive system, developed approximately 12 years ago. Two hundred five consecutive surgical procedures were examined, which was the first year of experience with RK for one of the authors (TPW). All procedures fit within the Casebeer nomograms. Enhancement procedures were performed following the Casebeer system nomograms. Follow-up for 100% of patients was achieved. Postoperative cycloplegic refractions yielded an average of +0.27 +/- 0.58 diopters (D) of residual refractive correction (range, -0.88 to +2.50 D). One year postoperatively, 20/25 or better uncorrected visual acuity was achieved in 86% of patients and 20/40 or better uncorrected visual acuity was achieved in 99% of patients. Bothersome but not incapacitating side effects, such as glare, starbursting, and fluctuating vision, have been commonly observed with RK. The Casebeer system for keratorefractive surgery, which is easy to learn, can yield an extremely accurate surgical result. The major reason for increased accuracy compared with the PERK system is the surgeon's ability to titrate the primary surgical procedure with enhancement operations. Although RK is by no means a perfect surgical technique, side effects tend to be relatively minimal, and patient satisfaction tends to be extremely high.

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study Five Years after Surgery

In the Prospective Evaluation of Radial Keratotomy (PERK) Study, 793 eyes of 435 patients with 2 to 8 diopters (D) of myopia received a standardized surgery consisting of 8 incisions with a diamond-bladed knife set at 100% of the thinnest paracentral ultrasonic corneal thickness measurement and a diameter of the clear zone of 3.0 to 4.5 mm; 97 eyes (12%) received an additional 8 incisions. There were 757 eyes (95%) followed for 3 to 6.3 years. After surgery, uncorrected visual acuity was 20/40 or better in 88% of eyes. The refractive error was within 1 D of emmetropia for 64% of eyes; 19% were myopic and 17% were hyperopic by more than 1 D. Between 6 months and 5 years after surgery, 22% of the eyes had a refractive change of 1 D or more in the hyperopic direction. For 25 eyes (3%) there was a loss of 2 or more lines of best spectacle-corrected visual acuity.

Corneal Topography as a Predictor of Refractive Change in the Prospective Evaluation of Radial Keratotomy (PERK) Study

The first operated eyes of 435 patients undergoing radial keratotomy in the Prospective Evaluation of Radial Keratotomy (PERK) study were evaluated by photokeratography to document the preoperative and postoperative corneal shape. We determined by regression analysis and analysis of variance that the corneal shape preoperatively improved the prediction of the corneal shape 6 months postoperatively in the 3-mm-clear-zone population. The reduction of myopia in all 435 eyes ranged from 1.25 to 9.75 diopters. We studied the effect of the preoperative corneal shape on this variability in the outcome of the surgery using rings 2 and 7 on photokeratography and corneal diameter. In the 3-mm-clear-zone group, eyes with flat prolate corneas had a greater reduction in myopia (4.65 D); those with steeper, more spherical corneas had less reduction in myopia (3.48 D). In addition, eyes with a 3-mm clear zone and flat central corneas alone (8.0 mm = 42.19 D) flattened approximately 0.75 D more than those with steep central corneas (7.0 mm = 48.21 D). In the 3.5-mm and 4.0-mm clear zone groups, the change in corneal curvature was not related to the preoperative curvature. A stepwise regression analysis of the 151 eyes in the 3.0-mm-clear-zone population demonstrated the following predictive equation for radial keratotomy; change in cycloplegic refraction = -14.55 + [-2.097 x average ring-2 radius] + [3.605 x average ring-7 radius] + [0.69 x horizontal corneal diameter] + [0.079 x age] + [-0.379 x spherical equivalent cycloplegic refraction]. There was a 1.17-D observed difference in the effect of radial keratotomy between those eyes with a steep/steep corneal topography (7.2% of the 3.0-mm-clear-zone population) and the flat/flat topography (29% of the 3.0-mm-clear-zone PERK population). A knowledge of corneal topography provides an additional tool for understanding the operative variability of radial keratotomy.

Contrast Sensitivity Under Photopic Conditions in the Prospective Evaluation of Radial Keratotomy (PERK) Study

We studied the effect of radial keratotomy on contrast sensitivity in 69 individuals with one eye operated and one eye unoperated in the Prospective Evaluation of Radial Keratotomy (PERK) Study, with a mean follow-up time of 13.8 months (range 6 months to 31 months). We tested contrast sensitivity under normal daylight conditions using both photographic plates and a computer-video apparatus. On average, we found no clinically meaningful loss of contrast sensitivity in eyes after radial keratotomy. However, eyes with radial keratotomy showed a statistically significant decrease in contrast sensitivity at the higher spatial frequencies of 12 and 18 cycles per degree, although all values were within the previously established normal range. Specifically, 44% of the patients had approximately the same contrast sensitivity in both eyes; 40% of the patients had 50% less contrast sensitivity in the operated eye than in the unoperated eye; 16% of the patients had 50% more contrast sensitivity in the operated eye than in the unoperated eye. Contrast sensitivity improved gradually in operated eyes between 6 months and 2 years after surgery. Eyes with radial keratotomy, in which the diameter of the pupil was the same size as or larger than the central clear zone, had slightly decreased contrast sensitivity compared to eyes in which the pupil was smaller than the clear zone.

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 Years After Surgery for Myopia

The Prospective Evaluation of Radial Keratotomy Study is a nine-center clinical trial of a surgical technique to reduce simple myopia by making incisions in the cornea. There were 435 patients (one eye per patient is reported) enrolled in the study with a 91% follow-up rate at 4 years after surgery. After surgery, uncorrected visual acuity was 20/40 or better in 76% of eyes. Fifty-five percent of the eyes had a refractive error within +/- 1.00 diopter; 28% were undercorrected, and 17% were overcorrected by more than 1.00 D. The width of the prediction 90% interval for the refractive change was 4.42 D, indicating a lack of predictability. The refractive error was not stable in some eyes; between 6 months and 4 years after surgery, 23% of eyes had a continued effect of the surgery of more than 1.00 D. For 323 patients with both eyes operated on, 64% stated they wore no optical correction. There were few serious complications. Eleven eyes (3%) lost two or three lines of best corrected visual acuity. Two eyes developed delayed bacterial keratitis without significant loss in best corrected visual acuity.

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. Perk Study Group

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. Perk Study Group

Radial Keratotomy in the 1990s and the PERK Study

When radial keratotomy was introduced into the United States, the procedure was performed using razor blade fragments whose extension was determined by sighting on a linear scale block; up to 24 or more incisions of various length per eye were used. As with any new procedure, significant complications occurred. The technique was declared "a risky procedure of unproven long-term success."¹The Prospective Evaluation of Radial Keratotomy (PERK) Study was begun in March 1982 as a nine-center trial with 10 participating surgeons that was designed to determine the outcome of a single standardized technique for simple (no astigmatism) myopia.²About the time the PERK Study began, current surgical procedures were just being applied by the majority of radial keratotomy surgeons (diamond blades, ultrasonic measurement of corneal thickness, reduction of the length and number of incisions to ⩽16).³In this issue ofThe Journal, Waring and coworkers⁴provide

RADIAL KERATOTOMY FOR MYOPIA: LONG-TERM OUTCOMES.

Radial keratotomy is a controversial procedure in which partial-thickness incisions are made in the cornea in an attempt to correct myopia. To address some of the claims made about the procedure, the authors of the multicenter Prospective Evaluation of Radial Keratotomy …

Symmetry of Refractive and Visual Acuity Outcome in the Prospective Evaluation of Radial Keratotomy (PERK) Study

In the Prospective Evaluation of Radial Keratotomy (PERK) study, the symmetry of refractive and visual acuity outcome was analyzed in 269 patients with bilateral radial keratotomy with a single operation in each eye. Patients were required to wait 1 year after surgery on the first eye before having surgery on the second eye. At 1 year after surgery on the second eye, 98% of patients had 3.00 diopters or less difference between their two eyes in the spherical equivalent of the cycloplegic refraction (100% before surgery), and 96% of patients had 3.00 D or less difference between their two eyes in the amount of refractive power in the vertical meridian (100% before surgery). Thus, surgically induced refractive anisometropia was not a major complication in the PERK study. However, 14% of patients had four to eight Snellen lines difference in the uncorrected visual acuity between their two eyes (1% before surgery), emphasizing that induced asymmetry of refraction is a potential clinical problem for some patients.

Morning-to-eveninf Change in Refraction, Corneal Curvature, and Visual Acuity 2 to 4 Years after Radial Keratotomy 1n 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.

Effect of radial keratotomy on the contrast sensitivity function.

A group of six patients had the radial keratotomy (RK) procedure carried out on one eye only as part of the Prospective Evaluation of Radial Keratotomy (PERK) study. Contrast sensitivity was measured in the operated and unoperated eyes of these patients under conditions of maximum correction and no over-correction. Analysis of variance indicated a significant reduction in the contrast sensitivity function (CSF) of the operated eye postsurgically when compared to the operated eye for all patients. Analysis of results for individual patients indicated that three of the six patients showed significant reductions in CSF between the two eyes. Reasons for these changes are offered in terms of the change in glare produced by the surgical procedure and the difference in spherical aberration of the eye.

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 highresolution 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.