Variables Affecting Rigid Contact Lens Comfort in the Collaborative ...

1040-5488/04/8103-0182/0 VOL. 81, NO. 3, PP. 182–188 OPTOMETRY AND VISION SCIENCE Copyright © 2004 American Academy of Optometry

ORIGINAL ARTICLE

Variables Affecting Rigid Contact Lens Comfort in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study TIMOTHY B. EDRINGTON, OD, MS, FAAO, RALPH E. GUNDEL, OD, FAAO, DAVID P. LIBASSI, OD, FAAO, HEIDI WAGNER, OD, FAAO, GILBERT E. PIERCE, OD, PhD, FAAO, JEFFREY J. WALLINE, OD, PhD, FAAO, JOSEPH T. BARR, OD, MS, FAAO, HARALD E. OLAFSSON, OD, FAAO, KAREN STEGER-MAY, MA, JOEL ACHTENBERG, MSW, BRAD S. WILSON, MA, MAE O. GORDON, PhD, KARLA ZADNIK, OD, PhD, FAAO, and THE CLEK STUDY GROUP Southern California College of Optometry, Fullerton, California (TBE), SUNY State College of Optometry, New York, New York (REG, DPL), NOVA Southeastern University, Ft. Lauderdale, Florida (HW), The Ohio State University College of Optometry, Columbus, Ohio (GEP, JJW, JTB, KZ), University of Utah, Department of Ophthalmology, Salt Lake City, Utah (HEO), Washington University School of Medicine, Division of Biostatistics (KS) and Department of Ophthalmology and Visual Science (JA, BSW, MOG), St. Louis, Missouri

ABSTRACT: Purpose. To identify factors associated with rigid contact lens comfort in keratoconus. Methods. Baseline data from the 16 Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study clinical sites were analyzed for all patients wearing a rigid contact lens in their more severely keratoconic eye (as determined by steep keratometry). Corneal transplant patients, patients who did not wear a rigid contact lens in either eye, patients who did not wear a rigid lens in their worse eye, and patients with missing contact lens comfort data were excluded from the sample. A total of 751 eyes were included. Variables assessed included measures of disease severity, visual acuity through the patients’ habitual rigid contact lenses, contact lens wearing time, the apical fitting relationship of the contact lens, the degree of peripheral clearance, and the presence of corneal scarring and staining. Comfort was measured by asking the patients “In general, how comfortable are your contact lenses?” (1 ⴝ very comfortable through 5 ⴝ very irritating). Results. Measures of disease severity (steep keratometry and the first definite apical clearance lens) were not associated with lens comfort. There was no difference in self-reported contact lens comfort between patients fitted with apical touch vs. apical clearance. Patients with a peripheral clearance rating of “minimal unacceptable” (more common among patients with milder keratoconus) were approximately half as likely to report good contact lens comfort compared with patients with “average” peripheral clearance (unadjusted odds ratio, 0.39; 95% confidence interval, 0.19 to 0.79). There was no association between contact lens comfort and the other peripheral clearance ratings compared with ratings of average. Conclusions. There does not appear to be an association between decreasing patient-reported rigid lens comfort and increasing disease severity as measured by steep keratometry or first definite apical clearance lens in this sample. The apical fitting relationship (flat vs. steep) does not appear to be associated with patient-reported comfort. Minimal peripheral clearance may contribute to decreased rigid contact lens comfort in keratoconus. (Optom Vis Sci 2004;81:182–188) Key Words: contact lens fitting, cornea, keratoconus, rigid gas-permeable contact lens

T

he Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a multicenter, longitudinal, observational study. The purpose of the CLEK Study is to prospectively characterize vision, corneal changes, and quality-of-life findings in keratoconus patients and to describe the progression of these

changes with time. Sixteen CLEK clinics enrolled 1209 eligible keratoconus patients between May 31, 1995 and June 29, 1996. Keratoconus is a progressive, asymmetric,1 noninflammatory disease of the cornea characterized by steepening and distortion of the cornea, apical thinning, and central scarring.2 This leads to a

Optometry and Vision Science, Vol. 81, No. 3, March 2004

Variables Affecting Rigid Contact Lens Comfort in the CLEK Study—Edrington et al.

mild to marked decrease in vision secondary to irregular astigmatism and/or central corneal scarring. There are several characteristic biomicroscopic corneal signs that become more prevalent as the disease progresses.3 According to the current literature, management varies with disease severity. Nonsurgical alternatives play a primary role in patient care of keratoconus. Although the visual disturbances in keratoconus may be managed with spectacle lenses or hydrogel contact lenses early in the disease process, rigid gas-permeable contact lenses are the treatment of choice for the irregular astigmatism associated with the disease. Sixty-five percent of the patients enrolled in the CLEK Study wore rigid gas-permeable contact lenses at the baseline visit, and most patients (73%) reported that their lenses were comfortable.4 Other investigators have reported similar rates of rigid contact lens wear in keratoconus.3, 5, 6 Rigid contact lens fitting philosophies for keratoconus are frequently characterized by the relationship between the base curve radius of the rigid contact lens and the curvature of the central cornea. This relationship is commonly described as either apical touch or apical clearance. Although numerous researchers have sought to describe the importance of the apical contact lens fitting relationship in keratoconus, its relationship to specific outcome measures is unclear.6 –14 Previous studies suggest that long-term rigid contact lens wear may be a risk factor for the development of keratoconus6, 14; that an apical touch fitting relationship may promote corneal scarring and ultimately contribute to the progression of the disease10; that fitting with apical touch results in statistically significant, but clinically insignificant, improved visual acuity12; and that fitting contact lenses with apical clearance may result in corneal molding.9 In this study, we sought to determine whether associations exist between patient-reported comfort and fitting variables such as the central fitting relationship, the degree of rigid contact lens peripheral (edge) clearance, and other contact lens parameter variables in keratoconus.

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acceptable, or excessive (Fig. 1). The patients’ habitual rigid lens parameters were measured at baseline. Parameters measured included base curve radius, contact lens power, overall diameter, optic zone diameter, and center thickness. The First Definite Apical Clearance Lens (FDACL) was determined by a method previously described.16 Briefly, the FDACL lens is the flattest lens that clears the apex of the cornea with fluorescein assessment of the fit. A standardized fitting set is used at each CLEK Study clinic.8 The clinician begins with the lens that is closest to the steep keratometric reading. If there is apical touch, the clinician applies steeper lenses until an apical clearance fluorescein pattern is achieved. Comparison of the base curve of this lens

METHODS The CLEK Study is a 16-center observational study of patients with keratoconus. A total of 1209 eligible patients were enrolled between May 31, 1995 and June 29, 1996. The investigators at each clinic obtained informed consent from their patients. The CLEK Study protocol was approved by each clinic’s institutional review board and is in accordance with the tenets of the Declaration of Helsinki. Data collected at the baseline visit have been previously described.4, 15, 16 Apical and peripheral fitting relationships of the patients’ habitual rigid contact lenses at baseline were evaluated by the clinician, and photographs of the fluorescein patterns were submitted for assessment to the CLEK Photography Reading Center located at The Ohio State University College of Optometry. The clinician graded (forced choice) the apical or central fitting relationship as definite touch, touch, clearance, or definite clearance. Due to the small number of ratings of clearance, apical relationship was dichotomized into touch or clearance. The clinician also averaged all quadrants of peripheral clearance and assigned a grade of minimal unacceptable, minimal acceptable, average, high

FIGURE 1. Representative photographs of peripheral clearance grades: (A) minimal acceptable; (B) average; and (C) high acceptable.


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to the habitual lens indicates how steep or flat the patient’s habitual contact lens is on the eye. Thus, an index of “flatness” was created by subtracting the base curve of the habitual lens from the base curve of the FDACL. Visual acuity was measured in three ways: entrance visual acuity (high- and low-contrast with habitual correction in each eye and then with both eyes); best corrected visual acuity (high- and lowcontrast with best correction [in rigid contact lens wearers, their rigid contact lenses with optimal over-refraction] in each eye); and manifest refraction acuity (high-contrast visual acuity in each eye). All high- and low-contrast visual acuities were performed at a testing distance of 4 m using Bailey-Lovie charts (School of Optometry, University of California, Berkeley).17 Visual acuity data for patients who were unable to read the top line of the chart at 4 m were excluded from this analysis. A “bothersome summary score” was created by averaging the patient’s responses to nine items designed to assess symptoms (itching, redness, burning, dryness, discomfort, excessive tearing, discharge, constant blur, and variable vision). Responses to the individual items were assessed on a four-point scale (0 ⫽ not experienced, 1 ⫽ somewhat bothersome, 2 ⫽ quite bothersome, and 3 ⫽ very bothersome). Corneal scarring was assessed by the clinician and a masked photograph reader at the CLEK Photography Reading Center as definitely not scarred, probably not scarred, probably scarred, or definitely scarred. We defined scarring as present when it was classified as definitely scarred by both the clinician and the CLEK Photography Reading Center reader and when it was located in the central 6 mm of the cornea as specified by the clinician. Corneal staining was classified as present when the clinician recorded the presence of “punctate, coalesced, or full-thickness epithelial defect” as “definitely present” in the central 6 mm of the cornea.15 Lens comfort was determined by asking the patients “In general, how comfortable are your lenses?” (1 ⫽ very comfortable, 2 ⫽ comfortable, 3 ⫽ mildly irritating, 4 ⫽ irritating, and 5 ⫽ very irritating). So few contact lenses were judged to be very irritating or irritating that the comfort scale was dichotomized into either comfortable or irritating for analytic purposes.

Statistical Methods Baseline data were analyzed on all patients wearing a rigid contact lens (rigid gas-permeable or polymethyl methacrylate) in their more severely keratoconic eye (as determined by the steeper keratometric reading in each eye). Unilateral corneal transplant patients at baseline (N ⫽ 118) were excluded from the sample. Patients who did not wear a rigid contact lens in either eye (N ⫽ 304), patients who did not wear a rigid contact lens in their worse eye (N ⫽ 28), and patients with missing contact lens comfort data (N ⫽ 8) were also excluded. A total of 751 eyes were eligible. Descriptive statistics for patient-specific variables were computed using all patients in the analysis. Descriptive statistics for eye-specific variables, e.g., keratometry, were computed using the patient’s more severely keratoconic eye. Logistic regression analysis was used to model contact lens comfort. Univariate (unadjusted) odds ratios and adjusted odds ratios

and their 95% confidence intervals were computed using available data from each patient. Variables with statistically significant odds ratios (p ⱕ 0.05) in the univariate logistic regression models became candidates for inclusion in the multiple logistic regression analysis. To achieve parsimony and statistical independence, only one measure of lens wearing time and one measure of visual acuity could be included in the multivariate model. Average daily wearing time and high-contrast entrance visual acuity were selected based on their univariate odds ratios. Adjusted odds ratios and corresponding 95% confidence intervals are reported for variables included in the multivariate model, adjusted for all variables in the model. Model fit was confirmed by assessing goodness-of-fit statistics. The data were analyzed using the Statistical Analysis System (version 8.2, 1999, SAS Institute, Cary, NC).

RESULTS Table 1 reports patient-specific and eye-specific factors and their univariate (unadjusted) odds ratios for 751 patients’ self-reported contact lens comfort. Descriptive data are reported for patients who reported their contact lens comfort as comfortable (N ⫽ 509 patients) or irritating (N ⫽ 242). Table 2 reports the odds ratios for factors included in the multiple logistic regression model of contact lens comfort. The univariate odds ratio indicates a 41% greater likelihood for better lens comfort with every decade of age; however, this association is not statistically significant in the multiple regression model. No association is found between lens comfort and sex, race, or a history of systemic disease. Better entrance visual acuity is associated with good contact lens comfort. The multivariate odds ratio indicates about a 12% greater likelihood for good lens comfort for every additional five letters correct of high-contrast entrance visual acuity. Contact lens comfort is associated with a 16% to 17% increase for each additional hour of contact lens wear per day during weekdays and weekends. Patients who remove their contact lenses more often are about half as likely to report good contact lens comfort. Patients who report more “bothersome” contact lenses are less likely to report good contact lens comfort. Patients with peripheral clearance ratings of “minimal unacceptable” are approximately half as likely to report good contact lens comfort than patients with “average” peripheral clearance. There is no difference in the likelihood of good contact lens comfort for the other edge clearance ratings compared with ratings of average. Measures of corneal curvature (the steeper keratometric reading and FDACL), contact lens base curve and overall diameter, corneal scarring, corneal staining, apical fluorescein pattern, tarsal papillae, and lens-induced imprint were not associated with good contact lens comfort. In the multiple regression model, better high-contrast entrance visual acuity, longer daily lens wearing time, and fewer lens removals were associated with a statistically significant increased likelihood of contact lens comfort.

DISCUSSION In normal, nonkeratoconic patients, rigid contact lens comfort is dependent on the interaction between the upper eyelid and the



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TABLE 1. Patient-specific and eye-specific factors for contact lens comfort at baselinea Comfort Variable

Patient-specific factors Agef Sex (% female) Race (% nonwhite) History of systemic diseasee Eye-specific factors Steep keratometry reading (D) % Steep K (D) ⬎52D FDACL (D) % FDACL (D) ⬎52D Habitual lens base curve (D) Habitual lens diameter (mm) Flatness (D) (FDACL-habitual BC) High-contrast, entrance VA (letters correct)f Low-contrast, entrance VA (letters correct)f Average daily lens wearing time in last 3 weekdays (hours) Average daily lens wearing time last weekend (hours) No. of times lenses removed daily Bothersome summary score Corneal scarring Corneal staining Apical fluorescein pattern (% touch) Fluorescein peripheral clearanceg Minimal, unacceptable Minimal, acceptable Average High, acceptable Excessive Moderate/severe limbal or bulbar injection Hypertrophy/giant tarsal papillae (upper or lower) Lens-induced imprint

Unadjusted Odds Ratiob

95% CIc

p Valued

36.74 ⫾ 10.68 45% 32% 60%

1.41 0.99 0.86 0.84

1.21, 1.64 0.73, 1.35 0.62, 1.20 0.62, 1.15

⬍0.0001 0.95 0.38 0.29

52.97 ⫾ 5.40 48% 52.72 ⫾ 5.25 46% 49.49 ⫾ 4.57 8.72 ⫾ 0.52 3.29 ⫾ 3.46 44.88 ⫾ 9.16 30.98 ⫾ 10.28 13.70 ⫾ 3.90

53.50 ⫾ 5.60 52% 53.12 ⫾ 5.49 49% 49.67 ⫾ 4.79 8.78 ⫾ 0.53 3.53 ⫾ 3.81 42.11 ⫾ 9.54 28.04 ⫾ 10.26 10.62 ⫾ 5.04

0.98

0.96, 1.01

0.21

0.99

0.96, 1.02

0.34

0.99 0.79 0.98 1.17 1.15 1.17

0.96, 1.03 0.59, 1.07 0.94, 1.02 1.08, 1.27 1.06, 1.24 1.13, 1.22

0.63 0.13 0.40 0.0002 0.0005 ⬍0.0001

13.36 ⫾ 4.06

9.85 ⫾ 5.47

1.16

1.12, 1.20

⬍0.0001

0.44 ⫾ 0.94 0.53 ⫾ 0.42 36% 38% 90%

1.05 ⫾ 1.40 1.00 ⫾ 0.60 31% 37% 93%

0.60 0.15 1.26 1.04 0.75

0.51, 0.70 0.10, 0.22 0.91, 1.74 0.76, 1.43 0.42, 1.34

⬍0.0001 ⬍0.0001 0.17 0.81 0.33

3% 16% 48% 26% 6% 9% 12% 15%

7% 18% 44% 23% 8% 15% 14% 15%

0.39 0.83 1.00 1.04 0.71 0.62 0.86 1.01

0.19, 0.79 0.01 0.53, 1.29 0.41 Reference category 0.70, 1.55 0.84 0.38, 1.32 0.28 0.39, 0.98 0.04 0.55, 1.36 0.52 0.66, 1.54 0.97

Comfortable (N ⫽ 509)

Irritating (N ⫽ 242)

40.59 ⫾ 10.68 45% 29% 56%

Continuous data are represented as mean ⫾ SD. Unadjusted odds ratio is calculated from univariate logistic regression modeling contact lens comfort. c CI, confidence interval; K, keratometry; FDACL, First Definite Apical Clearance Lens; BC, base curve; VA, visual acuity. d Variables with p ⬍ 0.05 selected for inclusion in final multivariate model. e Systemic disease defined as a history of hay fever, seasonal allergies, asthma, or atopic dermatitis. f Odds ratio for age is per decade. Odds ratio for acuities is per five letters. g Odds ratios for this variable compare each category with the “Average” category. a

b

lens edge. If the lens edge is excessively thick or the edge profile not appropriately contoured, lens comfort generally decreases.18, 19 Excessively flat-fitting lenses that position inferiorly tend to accentuate lid interaction and lead to discomfort. However, flat-fitting lenses that position superiorly underneath the upper eyelid tend to enhance comfort.20 Lenses with chipped edges or lenses that are excessively scratched or deposited with protein are also less comfortable. There does not appear to be an association between decreasing patient-reported rigid lens comfort and increasing disease severity as measured by steep keratometry and FDACL. Clinically, it is common for keratoconus patients to be increasingly intolerant to rigid contact lens wear. Contact lens intolerance, and the resulting

reduced contact lens wearing time, is a leading cause for corneal transplant in keratoconus.7 The finding of increased comfort resulting in increased wearing time is expected. However, in keratoconus, there is a confounding situation. As the disease becomes more advanced and best-corrected spectacle vision decreases, keratoconus patients become more dependent on their rigid contact lenses for functional vision. This may result in more hours of wearing time, even though there is a tendency for increases in other signs and symptoms of the disease. If a rigid contact lens becomes uncomfortable, patients may resort to instilling artificial tears and/or rewetting drops. These tend to only provide temporary relief. To provide a break from the discomfort of lens wear, many patients remove their lenses during


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TABLE 2. Multiple logistic regression model of factors associated with contact lens comfort at baseline Variable Ageb High-contrast, entrance VA (letters correct)a,c Average daily lens wearing time in last 3 weekdays (hours) No. of times lenses removed daily Bothersome summary score Fluorescein peripheral clearanced Minimal, unacceptable Minimal, acceptable Average High, acceptable Excessive Moderate/severe limbal or bulbar injection

Adjusted Odds Ratio

95% CIa

p Value

1.18 1.12 1.12 0.70 0.20

0.98, 1.40 1.01, 1.25 1.07, 1.17 0.58, 0.84 0.13, 0.30

0.08 0.03 ⬍0.0001 ⬍0.0001 ⬍0.0001

0.38 1.09 1.00 1.06 0.75 0.80

0.15, 0.97 0.04 0.65, 1.82 0.75 Reference category 0.67, 1.67 0.80 0.35, 1.61 0.46 0.46, 1.42 0.46

a

CI, confidence interval; VA, visual acuity. Odds ratio for age is per decade. c Odds ratio for acuities is per five letters. d Odds ratios for this variable compare each category with the “Average” category. b

wearing hours and reapply them. Even though patients wearing cosmetic rigid contact lenses may complain of ocular dryness or discomfort toward the end of their wearing schedule, few experience discomfort to the point of removing and reapplying their contact lenses. The apical fitting relationship (flat vs. steep) does not appear to be associated with patient-reported comfort. Theoretically, a flatfitting lens might increase lens awareness due to increased interaction and exposure of the lens edge to the upper eyelid. Conversely, a steep-fitting lens may expose the lens edge less because it would be “tucked” in at the edge, but the steep-fitting lens might restrict tear exchange and decrease comfortable wearing time. Patients with peripheral clearance ratings of minimal unacceptable are approximately half as likely to report contact lens comfort than patients with average peripheral clearance. It is generally more difficult to obtain adequate peripheral clearance on advanced cases of keratoconus. Therefore, this finding suggests that adequate peripheral clearance is important in maintaining patient comfort in keratoconus. In summary, there does not appear to be an association between decreasing patient-reported rigid lens comfort and increasing disease severity. The apical fitting relationship (flat vs. steep) does not appear to be associated with differences in patient-reported comfort. Minimal peripheral clearance may contribute to decreased rigid contact lens comfort in keratoconus.

APPENDIX The CLEK Study Group (as of April 2002). Clinical Centers University of Alabama at Birmingham School of Optometry, Birmingham, AL. William J. “Joe” Benjamin, OD, PhD (Principal Investigator); Carol Rosenstiel, OD (Co-Investigator); Maria S. Voce (Study Coordinator); Brian Marshall, OD (Co-Investigator, 1994 –1995); C. Denise Pensyl, OD, MS (Co-Investigator

1994 –2000). University of California, Berkeley School of Optometry, Berkeley, CA. Nina E. Friedman, OD, MS (Principal Investigator); Dennis S. Burger, OD (Co-Investigator); Kelly A. McCann, MFA (Administrative Assistant); Pamela Qualley, MA (Study Coordinator, 1994 –2001); Karla Zadnik, OD, PhD (Principal Investigator, 1994 –1996). University Hospitals of Cleveland and Case Western Reserve University, Department of Ophthalmology, Cleveland, OH. Loretta B. Szczotka, OD, MS (Principal Investigator); Beth Ann Benetz, MA (Photographer); Ellen Burnside (Photographer); Stephanie Burke (Back-up Photographer); Janet Edgerton, COT (Technician); Patricia Kane (Back-up Photographer); Jonathan H. Lass, MD (Co-Investigator); Kimberly L. Schach (Study Coordinator); Stephanie M. Shaffer, MA (Study Coordinator); Pamela A. Smith (Technician, 1999 –2002); Thomas Stokkermans, OD, PhD (Co-Investigator); Kimberly D. Supp (Technician, 1994 – 1999); Bonita Darby (Study Coordinator, 1994 –1996); Ellen M. Stewart (Photographer, 1995–1997); Laura A. Teutsch (Technician, 1995–1999). Gundersen Lutheran, La Crosse, WI. John L. Sterling, OD (Principal Investigator); Thomas M. Edwards, OD (Co-Investigator); Janet M. Hess (Study Coordinator/ Technician); John D. Larson, OD (Co-Investigator); Jill A. Nelson (Study Coordinator/Technician); John M. Sake (Photographer); Lorna J. Plenge (Technician, 1995–2001); Eric M. Sheahan (Photographer, 1995–1999). University of Illinois at Chicago Department of Ophthalmology, Chicago, IL. Timothy T. McMahon, OD (Principal Investigator); S. Barry Eiden, OD (Co-Investigator); Charlotte E. Joslin, OD (Co-Investigator); Tina M. Laureano (Study Coordinator); George A. Rosas (Technician); Brenda Smith (Technician); Tim Ehrecke (Photographer, 1994 –1995); Mildred Santana (Technician, 1997); Jamie L. Brahmbatt (Study Coordinator, 1994 –2000). Indiana University School of Optometry, Bloomington, IN and Indianapolis Eye Care Center, Indianapolis, IN.



Gerald E. Lowther, OD, PhD (Principal Investigator); Carolyn G. Begley, OD, MS (Co-Investigator); Donna K. Carter (Study Coordinator/Technician); Nikole L. Himebaugh, OD (Co-Investigator); Pete S. Kollbaum, OD (Co-Investigator); Colleen M. Riley, OD, MS (Co-Investigator); Lee M. Wagoner, MHA (Study Coordinator, 1996 –2000). Jules Stein Eye Institute UCLA, Los Angeles, CA. Barry A. Weissman, OD, PhD (Principal Investigator); Lilian L. Andaya (Study Coordinator); Doris M. Boudaie, OD (Co-Investigator); Melissa W. Chun, OD (Co-Investigator); Ronit Englanoff, OD (Co-Investigator); Elisabeth T. Lim (Technician); Louis Rosenberg, OD (Co-Investigator); Lisa A. Barnhart, OD (Co-Investigator, 1995–2001); Karen K. Yeung, OD (Co-Investigator, 1999 –2001). University of Missouri-St. Louis School of Optometry, St. Louis, MO. Larry J. Davis, OD (Principal Investigator); Edward S. Bennett, OD, MSEd (Co-Investigator); Beth A. Henderson, OD (Co-Investigator); Bruce W. Morgan, OD (Co-Investigator); Patricia Sanders, BS (Study Coordinator); Janene R. Sims, OD (Co-Investigator); Zansheree L. Blue (Study Coordinator, 2000 –2001); Monica J. Harris, OD (Co-Investigator, 2000 –2001); Amber A. Reeves, MA (Study Coordinator, 1998 –2000); Bruce W. Morgan, OD (Co-Investigator); Nancy M. Duquette (Study Coordinator, 1995–1998). State University of New York State College of Optometry, New York, NY. David P. Libassi, OD (Principal Investigator); Ralph E. Gundel, OD (Co-Investigator). Northeastern Eye Institute, Scranton, PA. Joseph P. Shovlin, OD (Principal Investigator); John W. Boyle, OD (Co-Investigator); J. Bradley Flickinger, OD (Co-Investigator); M. Elizabeth Flickinger, OD (Co-Investigator); Stephen C. Gushue (Photographer); Patricia McMasters (Study Coordinator); Cheryl Haefele (Study Coordinator, 1994 –2000); Stephen E. Pascucci, MD (Medical Monitor). Nova Southeastern University College of Optometry, Ft. Lauderdale, FL. Heidi Wagner, OD (Principal Investigator); Andrea M. Janoff, OD (Co-Investigator); Chris Woodruff, OD (Photographer); Arnie Patrick, OD (Study Coordinator); Julie A. Tyler, OD (Study Coordinator); Karla E. Rumsey, OD (Co-Investigator 1995). The Ohio State University College of Optometry, Columbus, OH. Barbara A. Fink, OD, PhD (Principal Investigator); Lindsay Florkey (Study Coordinator); Gregory J. Nixon, OD (Co-Investigator); Jason J. Nichols, OD, MS (Co-Investigator; Coordinator 1996 –2001); Susan L. Sabers, OD (Study Coordinator, 1994 – 1996); Lisa Badowski, OD, MS (Co-Investigator, 1995–1996). Pennsylvania College of Optometry, Philadelphia, PA. Joel A. Silbert, OD (Principal Investigator); Kenneth M. Daniels, OD (Co-Investigator); David T. Gubman, OD, MS (CoInvestigator, 1998 –2000); Mary Jameson (Back-up Study Coordinator); Theresa Sanogo (Study Coordinator). Southern California College of Optometry, Fullerton, CA. Julie Yu, OD (Principal Investigator); Raymond H. Chu, OD (Co-Investigator); Timothy B. Edrington, OD, MS (Co-Investigator; Principal Investigator, 1994 –2002); Eunice Myung, OD (Co-Investigator); Julie A. Schornack, OD, MEd (Co-Investigator); Terry Y. Tsang, OD (Co-Investigator, 1998 –2000). University of Utah, John Moran Eye Center, Department of Ophthalmology, Salt Lake City, UT.

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Harald E. Olafsson, OD (Principal Investigator); Doug M. Blanchard (Photographer); Deborah Y. Harrison, MS (Study Coordinator); Mark McKay, OD (Co-Investigator); Paula F. Morris (Photographer); Kim Wegner (Study Coordinator/Technician); Libbi A. Tracy, OD (Co-Investigator, 1995–1998); Kate M. Landro (Study Coordinator, 1995–1998); Lizbeth A. Malmquist (Technician, 1998); Marie Cason (Technician, 1995–1999); Craig M. Fehr (Technician, 1997–1999). Former Clinical Centers University of Texas at San Antonio Health Science Center Department of Ophthalmology, San Antonio, TX (1996). Julie A. Yu, OD (Principal Investigator); Beth Ann Benetz, MA (Photographer); E. Joseph Zayac, OD (Principal Investigator 1994 –1996); Paul D. Comeau (Photographer 1994 –1996); Ray V. Reil (Photographer 1994 –1996); Sandra J. Hunt (Technician 1994 –1996). Resource Centers Chairman’s Office, The Ohio State University College of Optometry, Columbus, OH. Karla Zadnik, OD, PhD (Chairman); Nora McFadden (Secretary); Jodi M. Malone, RN (Study Coordinator); Jeffrey J. Walline, OD, PhD (Optometrist); Dione Allen (Secretary, 1997–2000). CLEK Photography Reading Center, The Ohio State University College of Optometry, Columbus, OH. Joseph T. Barr, OD, MS (Director); Gilbert E. Pierce, OD, PhD (Reader); Marjorie J. Rah, OD, PhD (Reader, based at the New England College of Optometry); Mohinder Merchea, OD, PhD (Reader); Beth Ann Oglevee (Study Coordinator); Gloria Scott-Tibbs (Study Coordinator); Robert Steffen, OD, MS (Reader 1994 –1995); Roanne Flom, OD (Reader 1998 –2001). Coordinating Center, Washington University Medical School, Department of Ophthalmology &Visual Sciences and the Division of Biostatistics, St. Louis, MO. Mae O. Gordon, PhD (Director); Joel Achtenberg, MSW (Senior Research Analyst); Patricia A. Nugent (Data Assistant); Teresa A. Roediger (Project Manager); Kenneth B. Schechtman, PhD (Statistician); Brad S. Wilson, MA (Statistical Data Analyst); Michael Richman (Project Manager, 1994 –1996). CLEK Topography Reading Center, Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, IL. Timothy T. McMahon, OD (Director); Robert J. Anderson, PhD (Biostatistician); Dasia Corado (Reader); Michi Goto (Research Assistant); Thomas W. Raasch, OD, PhD (Consultant); Cynthia Roberts, PhD (Consultant); George A. Rosas (Study Coordinator); Loretta B. Szczotka, OD, MS (Consultant); Mark Wright, MS (Programmer/Analyst); Stephanie K. SchoepferGrosskurth (Reader, 2001); Stephanie Walter Cooper (Reader, 1998). Project Office, National Eye Institute, Rockville, MD. Donald F. Everett, MA. Executive Committee Karla Zadnik, OD PhD (Chairman); Joseph T. Barr, OD, MS; Mae O. Gordon, PhD; Timothy B. Edrington, OD, MS; Donald F. Everett, MA; Timothy T. McMahon, OD. CLEK Topography Analysis Group. Loretta B. Szczotka, OD, MS (Co-Chairman); Timothy T. McMahon, OD (Co-Chairman); Robert J. Anderson, PhD; Nina E. Friedman, OD, MS; Larry J. Davis, OD; Thomas W. Raasch, OD, PhD. Data Monitoring and Oversight Committee. Gary R. Cutter, PhD (Chairman); Robin L. Chalmers, OD; Bruce A. Barron, MD.


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ACKNOWLEDGMENTS The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) study is supported, in part, by the National Eye Institute, National Institutes of Health grants EY10419, EY10069, EY10077, and EY02687 and by Conforma Contact Lenses, Paragon Vision Sciences, CIBA Vision Corporation, and the Ohio Lions Eye Research Foundation. Submitted February 27, 2003; accepted November 10, 2003.

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Karla Zadnik The Ohio State University College of Optometry 338 West Tenth Avenue Columbus, OH 43210-1240 e-mail: [email protected]