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PubMedDate not supplied

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.

Adult↗
PubMedDate not supplied

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). We 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 three years after surgery, 58% of eyes had refractive error within one diopter of emmetropia; 26% were undercorrected, and 16% were overcorrected by more than one diopter. 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 diopters. Between one and three years after surgery, the refractive error changed by 1.00 diopter or more in 12% of eyes, indicating a lack of stability in some eyes.

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↗
PubMed2006

pERK, pAkt and pBad: a possible role in cell proliferation and sustained cellular survival during tumorigenesis and tumor progression in ENU induced transplacental glioma rat model.

Gliomas remain to be an unresolved medical problem. Better understanding of complex regulation and key molecules involved in glioma pathology are needed for designing new and effective treatment modalities. Activation of mitogen-activated protein kinase/extracellular signal regulated kinase (ERK) pathway is known to be having a critical role in cell proliferation and differentiation during the invasion and metastasis of the tumor cells. In the present study, N-ethyl N-nitrosourea induced glioma rat model was used to understand the role of ERK1/2 and Akt pathways in the progression of tumor malignancy. Twenty-four glioma rat brains of early (P90) and progressive (P180) stages were used for histological and immunoblot analysis. Results have shown increased levels of activated ERK1/2, activated Akt or protein kinase B, Bcl-2 and pBad in the glioma rats. This study may indicate increased cell proliferation and angiogenesis, mediated through activation of both ERK and Akt pathways along with increased levels of pBad. Further, pAkt and Bcl-2 levels in the progressive stage glioma rats may indicate existence of sustained tumor cell survival signals. Moreover, enhanced pBad levels in tumor may indicate that there are anti-apoptotic mechanisms, further making the malignant cells resistant to apoptosis.

Alkylating Agents↗
PubMed1983

Rationale for and design of the National Eye Institute Prospective Evaluation of Radial Keratotomy (PERK) Study.

A five-year, multicenter, collaborative clinical trial of radial keratotomy for myopia is being carried out at nine clinical centers. The study, funded by the National Eye Institute, is recruiting approximately 500 patients aged 21 years or older with -2.00 to -8.00 diopters of physiologic myopia who also meet other clearly defined eligibility criteria. Surgeons use a diamond-bladed micrometer knife to make eight radial incisions in the anterior cornea. The diameter of the central clear zone is determined by the amount of myopia and the depth of the incisions by intraoperative ultrasonic pachymetry. Investigators other than the surgeon gather all pre- and post-operative data. Examinations include measurement of visual acuity with standardized charts, verification of refractions by a second observer, measurement of corneal curvature by keratometry and photokeratoscopy, quantitation of glare with a glare tester, and measurement of the size of individual endothelial cells from specular photomicrographs with a computerized digitizer. A formal psychometric questionnaire is used to evaluate the patients' subjective response. Physician monitors insure adherence to the protocol during site visits and members of the Data and Safety Monitoring Board oversee the progress of the study. Biostatisticians at the Coordinating Center insure complete data collection, process the data, and assist in the interpretation of results.

Academies and Institutes↗