Biomedical subjects

M J Lynn

Publications and source records attributed to M J Lynn.

At least 37 records · Page 2Linked to original sources

PubMed1996

Pupillary response to tropicamide in patients with Alzheimer disease.

PURPOSE: To determine whether pupillary responses to dilute tropicamide could be used as a diagnostic test for Alzheimer disease (AD). The authors also investigated whether concurrent use of an oral acetylcholinesterase inhibitor (tacrine) alters the pupillary response to dilute tropicamide in patients with AD, and whether pupillary responses to dilute tropicamide differ in young versus older control subjects. METHODS: Pupillary diameter and area of both eyes were measured in light and darkness, at 10-minute intervals for 40 minutes after random instillation of 0.01% tropicamide to one eye. Four groups of subjects were studied: 9 patients with AD, 10 who were treated with tacrine, 11 older control subjects, and 10 young control subjects. RESULTS: Mean change in anisocoria was not significantly different among groups at any of the measurement time points. Mean percent change in diameter of the treated eyes showed a trend toward faster maximum dilatation in the AD groups, but change in pupillary measurements did not identify individuals with AD. CONCLUSION: Pupillary response to dilute tropicamide did not effectively distinguish individual patients with AD from young or older control subjects.

Adult↗

PubMed1996

Morning-to-evening change in refraction, corneal curvature, and visual acuity 11 years after radial keratotomy in the prospective evaluation of radial keratotomy study. The PERK Study Group.

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.

Circadian Rhythm↗

PubMed1995

Viability of human corneal endothelium following Optisol-GS storage.

OBJECTIVES: To evaluate endothelial viability of human corneas stored in glass vials and in viewing chambers (Alcon) for extended periods, and to compare endothelial viability of Optisol-GS-stored corneas with corneas excised from moist chamber-stored globes. METHODS: Endothelial viability was assessed using two staining techniques. Endothelium from stored corneas was stained with trypan blue combined with alizarin red S or stained with calcein AM-ethidium homodimer. Both techniques were used to determine which method is a more sensitive indicator of cytotoxic change. RESULTS: Corneas stored 4 to 21 days in Optisol-GS had a rate (mean +/- SE) of endothelial cell damage of 0.57% +/- 0.30% per day in vials and 0.69% +/- 0.27% in chambers. After storage intervals from 4 to 21 days, the Optisol-GS endothelium had an average decrease in viability of 9.5% to 16%. The endothelium of moist chamber eyes had a 44% to 59% decrease in viability after 2 to 5 days. After 24 hours, corneal endothelium of moist chamber eyes had less than 15% decrease in viability. Optisol-GS corneas stored for 35 to 56 days had greater than 50% decrease in endothelial viability. After 67 days, 95% to 100% of endothelial viability was lost. CONCLUSIONS: Corneas stored in Optisol-GS through 21 days at 4 degrees C maintain a high percentage of viable endothelial cells. There was no significant difference of endothelial viability between corneas stored in glass vials or in viewing chambers (Alcon). A 50% loss of endothelial viability occurred in moist chamber-stored corneas after 2 days and by 35 days in corneas stored in Optisol-GS.

Aged↗

PubMed1995

Conservative treatment of early-stage breast cancer in a medically indigent population.

The compliance with a program of breast-conservation treatment for early-stage breast cancer and the results of that treatment among women treated between January 1983 and January 1992 was investigated in a large inner-city public hospital serving a primarily black population. Medical records and charts were reviewed for 25 consecutive patients with stage I and II breast cancer seen in consultation in the radiation oncology department. Of those 25 patients, 20 underwent lumpectomy and radiation therapy. Survival, disease-free survival, and local recurrence-free survival were computed using the Kaplan-Meier method. Compliance was evaluated based on time to complete the prescribed course of radiotherapy after a lumpectomy. Five-year local recurrence-free survival for stage I and II patients was 95% (confidence interval [CI]: 71% to 99%). Five-year overall survival for stage II patients was 71% (CI: 31% to 92%), and disease-free survival was 74% (CI: 36% to 91%). This study demonstrates that a program of breast-conservation treatment for early-stage breast cancer can be implemented with good results, excellent treatment compliance, and 100% follow-up in a population of medically indigent women.

Adult↗

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

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↗

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↗

PubMed1991

Stability of refraction during four years after radial keratotomy in the prospective evaluation of radial keratotomy study.

The Prospective Evaluation of Radial Keratotomy Study is a nine-center clinical trial of a standardized technique of radial keratotomy in 435 patients who had simple myopia with a preoperative refraction between -2.00 and -8.00 diopters. We studied the stability of the refractive error during four years after surgery for each of 341 eyes first operated on that had a single surgical procedure. Between baseline and two weeks after surgery, all eyes became less myopic; between two weeks and three months, 161 eyes (59%) lost 1.00 D or more of the initial effect; and between three and six months, 266 eyes (95%) had a stable refraction with less than 1.00 D change. The change from six months to four years was less than 1.00 D for 246 eyes (72%). There was 1.00 D or more decrease in surgical effect (increased minus power) for 13 eyes (4%), and 1.00 D or more increase in surgical effect (decreased minus power) for 82 eyes (24%). Eyes with larger amounts of preoperative myopia and smaller diameter of the clear zone were more likely to have an increasing effect of the surgery. The duration of this continued increasing effect of the surgery is unknown.

Adult↗

PubMed1991

The relationship of visual acuity, refractive error, and pupil size after radial keratotomy.

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.

Adult↗

PubMed1991

Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. The Perk Study Group.

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.

Adult↗

PubMed1990

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

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.

Adult↗

PubMed1990

Reproducibility of normal corneal power measurements with a keratometer, photokeratoscope, and video imaging system.

To determine the reproducibility of currently available instruments for measuring corneal power, two investigators measured comparable locations on 18 normal human corneas using a keratometer (Bausch & Lomb, Rochester, NY), the Corneascope (Kera Corp, Santa Clara, Calif), and the Corneal Modeling System (Computed Anatomy Inc, New York, NY). (For the two keratoscopes, average powers around rings at comparable locations were used.) Comparisons made between instruments at the significance level of .05 indicated that the keratometer was more reproducible than the Corneal Modeling System and the Corneascope, and the Corneal Modeling System was more reproducible than the Corneascope. Of the 31 rings projected on the surface of each cornea by the Corneal Modeling System, rings 2 through 13 were read reasonably reproducibly in that 76% of the measurements on these rings differed by no more than 0.5 diopter. The Corneal Modeling System (software version 1.16) is 83% as reproducible as a keratometer reading at approximately the edge of the 3-mm central zone on normal human corneas and provides information about corneal topography in a more reproducible and visually useful manner than the other two instruments.

Adult↗

PubMed1989

Accuracy and precision of keratometry, photokeratoscopy, and corneal modeling on calibrated steel balls.

Surgical manipulation of corneal shape requires an accurate and precise method of measuring anterior corneal curvature from apex to limbus. We evaluated the accuracy and precision of the Bausch & Lomb Keratometer, Kera Corneascope, and Computed Anatomy Corneal Modeling System by measuring comparable locations on four calibrated steel test balls. The Keratometer and Corneal Modeling System were more accurate and precise than the Corneascope. No statistically significant difference was found between the Keratometer and Corneal Modeling System with respect to accuracy or precision. In addition, the accuracy and precision of all 31 rings of the Corneal Modeling System were studied. Rings 2 through 26 were read accurately and precisely within +/- 0.25 diopter on three of the four balls. Values on the steepest ball were within +/- 0.37 diopter.

Calibration↗

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

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↗

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

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↗