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ComparisonofFlatandSteepRigidContact
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1040-5488/05/8212-1014/0 VOL. 82, NO. 12, PP. 1014–1021
OPTOMETRY AND VISION SCIENCE
Copyright © 2005 American Academy of Optometry
ORIGINAL ARTICLE
Comparison of Flat and Steep Rigid Contact
Lens Fitting Methods in Keratoconus
KARLA ZADNIK, OD, PhD, FAAO, JOSEPH T. BARR, OD, MS, FAAO, KAREN STEGER-MAY, MA,
TIMOTHY B. EDRINGTON, OD, MS, FAAO, TIMOTHY T. McMAHON, OD, FAAO, and
MAE O. GORDON, PhD, THE COLLABORATIVE LONGITUDINAL EVALUATION OF
KERATOCONUS (CLEK) STUDY GROUP
The Ohio State University College of Optometry, Columbus, Ohio (KZ, JTB), the Department of Ophthalmology & Visual Sciences, Washington
University Medical School, St. Louis, Missouri (KSM, MOG), the Southern California College of Optometry, Fullerton, California (TBE),
and the Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois (TTM)
ABSTRACT: Purpose. The purpose of this article is to compare the safety and efficacy of flat- and steep-fitting rigid
contact lenses in keratoconus. Methods. The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a
16-center observational study. Cross-sectional results at baseline were generated for 1091 subjects with longitudinal
results from the 871 subjects who completed 8 years of follow up. Results. Of the 761 rigid contact lens-wearing
patients at baseline, 41% had a scar at baseline compared with 24% of the nonrigid contact lens wearers (odds ratio
[OR], 2.15; 95% confidence interval [CI], 1.35–3.43; p ⴝ 0.001). Eighty-seven percent were fitted with flat-fitting
lenses, whereas 13% were fitted with steep-fitting lenses. Rigid lens fitting method was also associated with incident
corneal scarring. A greater proportion of the corneas wearing flat-fitting contact lenses were scarred (43% compared
with 26% for the steep-fitted eyes; OR,ⴝ 2.19; 95% CI, 1.37–3.51; p ⴝ 0.001). After controlling for corneal curvature,
the association of rigid contact lens fit and corneal scarring at baseline did not persist (adjusted OR, 1.20; 95% CI,
0.70 –2.06; p ⴝ 0.52). Thirty-two percent of unscarred eyes at baseline fitted flat had developed an incident corneal
scar by the eighth year follow-up visit compared with 14% of eyes fitted steep (OR, 2.93; 95% CI, 1.34 – 6.42; p ⴝ
0.007). Conclusions. The data reported here indicate that, after controlling for disease severity in the form of corneal
curvature, keratoconic eyes fitted with a rigid contact lens resulting in an apical touch fluorescein pattern did not have
an increased risk of being scarred centrally at baseline. This “natural history” sample cannot determine causal
proof that one method of fitting lenses is safer than another. To achieve this, a randomized clinical trial is needed.
(Optom Vis Sci 2005;82:1014–1021)
Key Words: keratoconus, contact lens, rigid contact lens, CLEK Study
B
efore the availability of modern contact lenses, keratoconus
could not readily be optically corrected. Spectacles cannot
adequately correct the irregular astigmatism present in keratoconus, so before contact lenses, corneal surgery was the only
recourse. After diagnosing keratoconus and establishing a need for
improved vision beyond that which can be achieved with spectacles, rigid contact lenses are the method of choice for optimizing
vision and managing the irregular astigmatism (higher-order aberrations) associated with keratoconus.1 The clinical objective is to
provide the best vision, comfort, and wearing time possible while
minimizing any adverse effect on corneal physiology from the contact lens.
Soft contact lenses are unable to correct significant amounts of
irregular astigmatism, thus, gas-permeable contact lenses are required for mild, moderate, and advanced keratoconus.2–11 These
lenses may be fitted flat (touching the center or apex of the cornea)
or steep (clearing the corneal apex). Newer lens designs are fundamentally similar to these traditional designs with their own regimented fitting paradigms. For example, the Rose K Lens for Keratoconus was developed in New Zealand. It is a quadricurve (base
curve plus three peripheral curves) rigid gas-permeable lens and has
gained some popularity in the very recent past, but only one study
has rigorously examined the Rose K lens for safety and/or efficacy.12
Although rigid contact lenses provide improved vision, they also
have the potential to damage the cornea. One study even indicts
Optometry and Vision Science, Vol. 82, No. 12, December 2005
Contact Lens Fitting Methods in Keratoconus—Zadnik et al.
rigid contact lens wear as a precursor to and cause of keratoconus in
some cases.13 Scarring of the central cornea may occur in keratoconus without contact lens wear,14 but it is possible that contact
lenses can hasten axial scarring.15 Whether by causing hypoxia,
entrapment of biodebris and tears, or physical trauma, the contact
lens may induce deep central corneal abrasions. As a result of the
loss of epithelial layers, disruption of the anterior limiting membrane and Bowman’s membrane, and disruption of the regular
anterior stroma collagen structure, the central cornea may become
scarred16—and thus the vision reduced17—secondary to contact
lens wear in keratoconus.
The primary techniques for fitting rigid lenses in keratoconus
(as described by Korb et al15) are: (1) flat, with primary lens support on the apex of the cornea,18 in which the central optic zone of
the lens actually touches or “bears on” the central cornea; (2) steep,
with lens support and bearing directed off the apex and onto the
paracentral cornea, with clearance (vaulting) of the apex of the
cornea19; and (3) divided support, or “three-point touch,” with
lens support and bearing shared between the corneal apex and the
paracentral cornea. Early on, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study investigators made a decision
to force analyses to classify and analyze fluorescein patterns as
either flat or steep, because it is the investigators’ opinion that true
three-point touch fitting patterns, neither flat or steep, are difficult
to achieve and maintain. Years of experience grading of fluorescein
patterns at the CLEK Photography Reading Center have borne out
that observation (unpublished data).
Most eye care practitioners who fit rigid contact lenses for keratoconus continue to use central corneal touch fitting because it is
easier and appears to provide better vision, comfort, and wearing
time.20 Eighty-eight percent of patients in the CLEK Study who
wore rigid contact lenses at study enrollment had been fitted with
or were wearing flat lenses.21 In addition, it has been argued that
flat lenses delay the need for surgery by physically keeping the
shape of the cornea relatively flat.22 In contrast, it has been argued
that the flat-fitting philosophy may actually increase the risk of
corneal compromise in the form of scarring.15
The main reasons for and against fitting with these two methods
1015
are summarized in Table 1. Flat-fitting rigid contact lenses may
accelerate the time to onset, the rate, and the severity of corneal
scarring associated with keratoconus. Flat-fitting contact lenses are
thought to mechanically traumatize the already fragile keratoconic
cornea causing epithelial erosion and abrasion. Wilson and Kim
suggest that epithelial trauma can result in changes in corneal stromal keratocyte activity.16 Intuitively, a steep-fitting contact lens
appears less likely to cause mechanical trauma to the corneal apex.
The idea that steep-fitting lenses cause less corneal scarring
comes from a small clinical trial on seven patients in whom one eye
was randomized to a flat-fitting contact lens, whereas the fellow eye
was randomized to a steep-fitting contact lens, a problematic design because of the known asymmetry of keratoconus.23 The 12month incidence of corneal scarring in the seven eyes randomized
to flat-fitting contact lenses was 57% compared with 0% in the
seven contralateral eyes randomized to steep-fitting contact lenses.15 High rates of corneal erosion have also been reported in a
nonrandomized, prospective series (without a control group) by
Maguen et al, who reported a three-year incidence of “clinically
important” central corneal staining in three of 12 patients (25%)
prescribed flat-fitting rigid contact lenses.7
The purpose of this article is to analyze the CLEK Study data to
compare the safety and efficacy of flat- and steep-fitting contact
lenses in the management of keratoconus. The CLEK Study is an
observational study of keratoconus patients as they are routinely
cared for by eye care practitioners in the United States, and the
CLEK investigators do not intervene with regard to the enrolled
patients’ treatment.
METHODS
CLEK Study Design
The CLEK Study is a 16-center observational study of patients
with keratoconus.24 In total, 1209 eligible patients (Table 2) were
enrolled between May 31, 1995, and June 29, 1996. All patients
signed an informed consent document that had been approved by
the Institutional Review Board at the clinic site at which they were
examined. Of these, 116 patients had undergone penetrating ker-
TABLE 1.
Generally agreed-on advantages and disadvantages of two contact lens fitting methods in keratoconus (central corneal
touch—flat vs central corneal clearance—steep)
Advantages
Disadvantages
Flat
Easier to fit
Better visual acuity (or no worse than steep)
More comfortable for many patients
Physically flattens the cornea, suggested slowing of disease
progression
Delays the need for surgery as a result of extreme conus,
which cannot be fitted with contact lenses
Steep
Decreased scarring
Less likely to need surgery as a result of scarring
Fewer emergency visits
Initially comfortable for more patients (but for fewer hours)
Causes epithelial disruption
Increased scarring leads to increased need for surgery
More corneal abrasions (no lens wear for days)
Poorer short-term comfort
Increased number of emergency office visits resulting from
abrasions
Difficult to fit
Peripheral corneal disruption
Poorer long-term comfort (fewer usable hours of wear per day)
Increased practitioner and patient time and expense
Optometry and Vision Science, Vol. 82, No. 12, December 2005
1016
Contact Lens Fitting Methods in Keratoconus—Zadnik et al.
TABLE 2.
CLEK Study eligibility criteria
Inclusion Criteria
Age
Irregular corneal surface
Slit lamp biomicroscopic findings
Follow-up status
At least 12 years old
In either eye as observed by distortion of the keratometric mires, scissoring of the
retinoscopic reflex, or irregularity in the red reflex observed with the direct
ophthalmoscope
Vogt’s striae or a Fleischer’s ring of at least 2 mm arc or corneal scarring characteristic of
keratoconus in either eye
Able to complete at least three years of follow up
Exclusion Criteria
Surgical status
Other ocular disease
Bilateral corneal transplants
Nonkeratoconic ocular disease in both eyes such as cataract, intraocular lens implants,
macular disease, optic nerve disease other than glaucoma (e.g., optic neuritis, optic
atrophy)
atoplasty in one eye, and two patients had undergone epikeratoplasty in one eye before enrollment in the study. A complete summary of measurement methods has been published previously.24
Methods pertaining to this particular article are described subsequently.
Cross-sectional results at baseline were generated for the 1091
subjects enrolled in the CLEK Study excluding those who had
undergone penetrating keratoplasty or epikeratoplasty in one or
both eyes. For the purposes of the longitudinal analyses reporting
incident corneal scarring, we chose the 871 subjects who completed 8 years of follow up. One eye from each included subject was
randomly selected for analysis, trying to use as many eyes as possible in each analysis. Eyes without surgery at baseline (penetrating
keratoplasty or epikeratoplasty), eyes that wore rigid gas permeable
lenses at baseline, and eyes with incident scars by year 8 were given
precedence for selection.
Survey
Patients answered a series of questions about their ocular health,
general health, and contact lens history by completing a written
survey. These included contact lens-wearing time and contact lens
comfort.
Examination
A detailed examination was performed on each eligible patient.
Distance visual acuities were measured using the available highand low- (Michelson contrast 10%) contrast Bailey-Lovie charts25
(School of Optometry, University of California, Berkeley, CA).
The chart was located 4 m from the patient, and the white background of the chart had a standard luminance, which was calibrated at least weekly. If the patient could not correctly identify all
five of the letters on the top line of the Bailey-Lovie chart at 4 m,
the patient was moved forward to a 1-m test distance.
Visual acuity was measured as follows: (1) entrance visual acuity:
high and low contrast with habitual correction for each eye separately and with both eyes together; and (2) best-corrected visual
acuity: high and low contrast with best correction (for rigid contact
lens wearers: their rigid contact lenses with optimal, spherocylin-
drical overrefraction; for those patients who did not wear rigid
contact lenses: a CLEK Study trial contact lens with base curve
radius equal to the steep keratometric reading plus optimal overrefraction) for each eye separately. During each measure, patients
read the chart beginning at the top until they missed at least three
letters on a line after they had attempted to read every letter. Visual
acuity scores were recorded as the total number of letters correct.
Fluorescein patterns of habitual contact lenses were assessed.
Fluorescein was instilled, and the contact lens fit was observed by
slit lamp biomicroscopy with cobalt and Wratten 12 (or Tiffen
yellow) filters in place. A grading system using photographic standards specifying the central fluorescein pattern as definite touch,
touch, clearance, or definite clearance for each observation was
used. Clinicians used this grading system, and their assessment of
the central fluorescein pattern was used to define a flat fit (definite
touch or touch) and a steep fit (definite clearance or clearance). Peripheral clearance was graded as minimum/unacceptable, minimum/
acceptable, average, maximum/acceptable, or excessive/bubbles.
A protocol for determining the First Definite Apical Clearance
Lens (FDACL) to provide a measure of corneal curvature was
developed specifically for the CLEK Study (Edrington, 1998, no.
301). A rigid contact lens from the CLEK Study trial lens set with
a base curve radius equal to the steep keratometric reading was
applied. If the initial trial lens was judged to touch centrally, a
steeper trial lens was applied to the eye for fluorescein pattern
evaluation. This procedure was repeated until an apical clearance
pattern was achieved. The objective of the contact lens fitting
procedure was to locate the flattest lens in the trial lens set that
exhibited a definite apical clearance fluorescein pattern such that
the sagittal depth of the base curve chord diameter was greater than
the sagittal depth of the cornea for the same chord diameter. If the
initial trial lens was judged to be steep centrally, a flatter trial lens
was applied to the cornea for fluorescein pattern evaluation. This
procedure was repeated until apical touch was observed. The
CLEK Study trial lens set’s base curve radii were measured
monthly to ensure that the lenses were in the proper order and that
none of the lenses was warped. The fluorescein pattern of the
FDACL and the lens with a base curve radius 0.2 mm flatter were
photographed. Exposed but undeveloped film was mailed to the
Optometry and Vision Science, Vol. 82, No. 12, December 2005
Contact Lens Fitting Methods in Keratoconus—Zadnik et al.
CLEK Photography Reading Center (CPRC) at The Ohio State
University College of Optometry for centralized developing, labeling, and grading for quality control purposes.
Four parallel Epiped photographs of the central cornea were
taken, and the CLEK standardized corneal photography protocol
was used to document the presence or absence of corneal scarring
(Barr, 1996, no. 207). After pupillary dilation, four oblique photographs were taken of the entire cornea. Exposed but undeveloped
film was mailed to the CPRC for centralized development, labeling, and grading. Corneal scarring was also scored by the photograph readers as definitely not scarred, probably not scarred, probably scarred, and definitely scarred and was graded for density and
location. An eye was classified as scarred at baseline if either the
clinician or the CPRC classified the cornea as either probably or
definitely scarred and indicated that the scar was within the central
6 mm (diameter) of the cornea. An eye with incident scarring by
year 8 was defined as any cornea identified as probably or definitely
scarred at one or more follow-up visits (years 1 to 8) by both the
clinician and the CPRC that was not scarred at the baseline visit. In
addition, the CPRC identified the scar as central in location
(within a central 6-mm diameter region of the cornea).
Rigid contact lens parameters were measured. Parameters measured included base curve radius, contact lens power, overall diameter, optic zone diameter, and center thickness.
Statistical Methods/Sample Selection
Logistic regression analysis was used to determine the association of select independent variables with scarring. Univariate (unadjusted) odds ratios (ORs) and adjusted ORs (adjusted for
FDACL in diopters) and corresponding 95% confidence intervals
(CIs) were computed using the available data from each patient.
Between-group comparisons of select baseline variables were performed using unpaired t-tests.
For outcome measures evaluated at baseline and at year 8, longitudinal analyses were carried out using analysis of covariance
(ANCOVA) with the year 8 values as the dependent variable and
the baseline values as a covariate. Additional analyses also included
FDACL in diopters as a covariate.
Data are presented as mean ⫾ standard deviation (SD). The
data were analyzed using SAS (version 8.2, 1999; SAS Institute,
Inc., Cary, NC).
Rigid lens wearers were those patients who said they were wearing either rigid gas-permeable or polymethylmethacrylate contact
lenses at baseline, who had their entrance visual acuity measurements performed with their lenses in, and who had an assessment
of a fluorescein pattern recorded by the clinician.
RESULTS
Cross-Sectional Data: Baseline Associations of
Contact Lens Wear and Corneal Scarring, Visual
Acuity, and Contact Lens Wearing Time/Comfort
At baseline, 80% of the eyes (868 of 1091 eyes) habitually wore
some type of contact lenses. Thirty-nine percent of these contact
lens-wearing eyes (337 of 868 eyes) were scarred compared with
15% of eyes (33 of 223 eyes) not wearing contact lenses (univariate
OR, 3.65; 95% CI, 2.46 –5.42; p ⬍ 0.0001). Prevalent corneal
1017
scarring was associated with a 7% increase for each additional hour
of contact lens wear per day (univariate OR, 1.07; 95% CI, 1.04 –
1.11; p ⬍ 0.0001).
Six hundred ninety-nine of the 868 subjects (81%) wore rigid
contact lenses in both eyes at baseline, whereas 62 (7%) wore a
rigid lens in one eye and 107 (12%) did not wear a rigid lens in
either eye.
Of the 761 patients who entered the study wearing rigid contact
lenses, 41% (311 of 761 eyes) had a scar at baseline compared with
24% (26 of 107 eyes) nonrigid contact lens wearers (OR, 2.15;
95% CI, 1.35–3.43; p ⫽ 0.001). Eighty-seven percent (660 of 761
eyes) were fitted with flat-fitting lenses, whereas 13% (101 of 761
eyes) were fitted with steep-fitting lenses. Furthermore, among the
rigid contact lens-wearing eyes at baseline, a greater proportion of
the corneas wearing flat-fitting contact lenses were scarred (285 of
660 eyes [43%] compared with 26 of 101 eyes [26%] for the
steep-fitted eyes; OR, 2.19; 95% CI, 1.37–3.51; p ⫽ 0.001).
The relationship between type of contact lens fit (flat or steep)
and corneal scarring is confounded by disease severity, however. It
is probable that more severe cases of keratoconus are fitted with
rigid contact lenses and that more of those wearing rigid contact
lenses wear flat-fitting lenses. We cannot directly, reliably estimate
the incidence of corneal scarring in keratoconus patients who do
not wear rigid contact lenses, because most of the patients are rigid
lens wearers. Of the 64 patients not wearing rigid contact lenses at
baseline who were seen for their year 8 follow-up visit, 20 (31%) of
them had an incident scar, i.e., they had developed a corneal scar by
the end of the eighth year of follow up. Of these 20, eight patients
(40%) wore a rigid contact lens to at least one follow-up visit
between years 1 and 8. Of the 44 patients who wore a rigid lens at
baseline and did not have an incident scar, 16 of them (36%) wore
a rigid lens to at least one follow-up visit between years 1 and 8.
After controlling for disease severity (corneal curvature as assessed by FDACL), the association of rigid contact lens fit and
corneal scarring at baseline did not persist (adjusted OR, 1.20;
95% CI, 0.70 –2.06; p ⫽ 0.52), and steeper corneal curvature
increased the risk of prevalent corneal scarring by 28% per diopter
of increased curvature (adjusted OR, 1.28; 95% CI, 1.23–1.34;
p ⬍ 0.0001).
Within the flat-fitted rigid contact lens group (660 eyes), the
degree of flatness of the contact lens fit can be calculated
(FDACL—rigid contact lens base curve in D). The average fit was
3.31 D ⫾ (SD) 3.25 D flatter than the FDACL (OR, 1.19; 95%
CI, 1.13–1.26; p ⬍ 0.0001). For each additional diopter of habitual lens “flatness,” there was a 19% increase in the likelihood of a
corneal scar.
Flat-fitting lenses provided worse visual acuity on average than
did steep-fitting lenses, as shown in Table 3, without accounting
for disease severity. Flat- and steep-fitting lenses provided similar
patient-reported contact lens wearing time and comfort (Table 3).
Longitudinal Data: Associations of Contact Lens
Wear and Incident Corneal Scarring
Eight hundred seventy-one patients were seen for their year 8
follow-up visit. The next series of analyses excluded those eyes
scarred at baseline (n ⫽ 286) and eyes missing scarring data (n ⫽
3). Rigid contact lens wear at baseline, regardless of how they were
Optometry and Vision Science, Vol. 82, No. 12, December 2005
1018
Contact Lens Fitting Methods in Keratoconus—Zadnik et al.
TABLE 3.
Efficacy of rigid contact lenses as a function of contact lens fitting relationship at baseline*
Monocular entrance visual acuity (letters correct)
High contrast
Low contrast
Monocular best-corrected visual acuity (letters correct)
High contrast
Low contrast
Contact lens-wearing time (hours)
Unpaired
t-test p value
Flat (n ⫽ 660)
Steep (n ⫽ 101)
45.33 ⫾ 9.19
31.15 ⫾ -10.86
48.79 ⫾ 9.38
35.99 ⫾ 11.80
0.0005
⬍ 0.0001
47.35 ⫾ 8.79
32.69 ⫾ 10.75
50.47 ⫾ 7.65
37.84 ⫾ 9.46
0.0008
⬍ 0.0001
13.04 ⫾ 4.09
13.13 ⫾ 3.60
0.84
1.48 ⫾ 1.14
1.38 ⫾ 1.16
0.40
Contact lens comfort (0–4 scale)
*All data are presented as mean ⫾ standard deviation at baseline as a function of flat or steep rigid contact lens fit. The contact lens
fluorescein pattern is determined by the clinician. Contact lens wearing time and comfort are as reported by the patient to the clinician.
One eye is randomly selected from each patient.
fitted, was associated with incident corneal scarring. Three hundred seventy of 582 nonscarred eyes (64%) wore rigid contact
lenses at baseline. One hundred six of them (29%) had developed
corneal scarring by the end of the eighth year of follow up, whereas
42 of the 212 nonrigid lens wearers (20%) had developed corneal
scarring by the end of the eighth year of follow-up (OR, 1.62; 95%
CI, 1.08 –2.44; p ⫽ 0.02). This translates to a 62% increase in an
eye’s risk of scarring if that eye wears a rigid contact lens for keratoconus compared with eyes that did not wear rigid lenses.
The rigid lens fitting method was also associated with incident
corneal scarring (Table 4). Thirty-two percent (98 of 311) of unscarred eyes at baseline fitted flat had developed an incident corneal
scar by the eighth year follow-up visit compared with 14% (8 of
59) of eyes fitted steep (OR, 2.93; 95% CI, 1.34 – 6.42; p ⫽
0.007). Examined by disease severity, the same relation was seen
for patients with moderate keratoconus only (OR, 3.08; 95% CI,
1.05–9.07; p ⫽ 0.04). Only four patients with mild keratoconus at
baseline had developed an incident corneal scar by year 8. Controlling for disease severity (corneal curvature as assessed by the
FDACL), the risk of corneal scarring did not increase with flat
versus steep rigid contact lens fit (adjusted OR, 1.83; 95% CI,
0.79 – 4.23; p ⫽ 0.16). Steeper corneal curvature increased the risk
of corneal scarring by 26% per diopter of increased curvature (adjusted OR, 1.26; 95% CI, 1.17–1.35; p ⬍ 0.0001).
TABLE 4.
Number of incident scarred eyes through the eighth year of
follow-up as a function of rigid contact lens fitting relationship and disease severity at baseline*
Flat (n ⫽ 311)
Mild
Moderate
Severe
Total
Steep (n ⫽ 57)
No scar
Scar
No scar
Scar
Total
24
158
31
213
3
59
36
98
15
33
1
49
1
4
3
8
43
254
71
368
*Disease severity is specified by corneal curvature (FDACL)25:
mild less than 45.00 D; moderate from 45.00 to 52.00 D; severe
greater than 52.00 D.
Table 5 depicts visual acuity (best-corrected, high- and lowcontrast; entrance, high- and low-contrast) as a function of contact
lens fit, FDACL, and time. In general, the average change in any
disease severity group for any visual acuity measure is small. The
greatest decrease in visual acuity is seen for low-contrast, entrance
visual acuity in the patients with FDACL in the severe range at
baseline who were also fitted steep at baseline (n ⫽ 4 patients;
average change of – 6.00 ⫾ 3.46 letters correct).
DISCUSSION
It has been hypothesized that rigid contact lens use may actually
cause keratoconus. Macsai and colleagues observed that patients
who reported that their rigid contact lens use preceded their diagnosis of keratoconus tended to have less severe keratoconus,13 but
the reliability of a patient’s self-report on issues like diagnosis and
treatment can be called into question. The data in this article,
although not contributing to the question of causation of keratoconus by rigid lens wear because all of the patients had keratoconus
at baseline, show an association between rigid lens wear and corneal scarring. However, corneal scarring, rigid contact lens wear,
and the rigid contact lens fitting method chosen are all associated
with more severe keratoconus.
The issue of whether the method by which rigid contact lenses
are fitted in keratoconus actually causes the disease to worsen
and/or corneal scarring to form is more than 20 years old.15 The
problem with answering it with cross-sectional data is that even if
corneal scarring is associated with flat-fitting contact lenses, corneal scarring is also associated with more severe disease17 and practitioners are more likely to fit rigid contact lenses a great deal flatter
than the cornea in patients with steeper corneas.21 The data reported here indicate that, after controlling for disease severity in
the form of corneal curvature, a keratoconic eye fitted with a rigid
contact lens resulting in an apical touch fluorescein pattern did not
have an increased risk of being scarred centrally at baseline.
Likewise, the longitudinal data show that the risk of flat-fitting
lenses in producing apical corneal scarring is not borne out after
controlling for disease severity. Although the CLEK Study provides information on the annual incidence of scarring in keratoco-
Optometry and Vision Science, Vol. 82, No. 12, December 2005
Contact Lens Fitting Methods in Keratoconus—Zadnik et al.
1019
TABLE 5.
Visual acuity as a function of rigid contact lens fit and disease severity*
Flat at Baseline (n ⫽ 311)
Mild
(n ⫽ 27)
High contrast
Baseline 53.48 ⫾ 5.86
Best-corrected Year 8
51.92 ⫾ 7.29
visual acuity Change ⫺1.56 ⫾ 6.75
Steep at Baseline (n ⫽ 57)
Moderate
(n ⫽ 217)
Severe
(n ⫽ 67)
Mild
(n ⫽ 16)
Moderate
(n ⫽ 37)
Severe
(n ⫽ 4)
50.60 ⫾ 6.48
49.32 ⫾ 7.93
⫺1.28 ⫾ 7.35
49.08 ⫾ 5.79
48.50 ⫾ 6.17
⫺0.58 ⫾ 5.74
55.25 ⫾ 9.73
54.38 ⫾ 6.46
⫺0.88 ⫾ 8.69
51.38 ⫾ 6.20
51.11 ⫾ 6.05
⫺0.27 ⫾ 6.48
42.00 ⫾ 7.00
36.00 ⫾ 7.81
⫺6.00 ⫾ 3.46
35.70 ⫾ 7.66
32.70 ⫾ 7.51
⫺3.00 ⫾ 8.53
45.19 ⫾ 9.89
40.81 ⫾ 7.52
⫺4.38 ⫾ 9.39
39.14 ⫾ 8.18
37.78 ⫾ 8.85
⫺1.35 ⫾ 7.81
32.00 ⫾ 6.24
26.67 ⫾ 2.31
⫺5.33 ⫾ 8.50
Low contrast
Baseline 41.96 ⫾ 6.13
37.11 ⫾ 7.81
Best-corrected Year 8
36.72 ⫾ 10.00 34.48 ⫾ 10.24
visual acuity Change ⫺5.24 ⫾ 7.14 ⫺2.63 ⫾ 9.80
High contrast
Entrance
Baseline 53.04 ⫾ 6.07
Year 8
51.41 ⫾ 5.56
Change ⫺1.63 ⫾ 7.91
48.46 ⫾ 6.95
46.48 ⫾ 9.84
⫺1.98 ⫾ 9.78
47.24 ⫾ 5.79
45.51 ⫾ 10.44
⫺1.73 ⫾ 11.20
54.19 ⫾ 10.56
53.13 ⫾ 5.90
⫺1.06 ⫾ 6.29
50.24 ⫾ 4.54
49.38 ⫾ 5.24
⫺0.86 ⫾ 5.69
42.00 ⫾ 9.45
41.00 ⫾ 11.22
⫺1.00 ⫾ 4.24
Low contrast
Entrance
Baseline 40.15 ⫾ 7.16
Year 8
37.22 ⫾ 9.94
Change ⫺2.93 ⫾ 9.37
35.71 ⫾ 8.82
31.70 ⫾ 11.30
⫺4.01 ⫾ 12.08
33.21 ⫾ 7.47
28.43 ⫾ 14.02
⫺4.78 ⫾ 15.95
44.25 ⫾ 10.14
41.13 ⫾ 9.71
⫺3.13 ⫾ 5.63
38.14 ⫾ 8.19
34.46 ⫾ 8.69
⫺3.68 ⫾ 8.51
30.00 ⫾ 8.76
30.50 ⫾ 15.46
0.50 ⫾ 11.12
*Cells contain the number of letters correct (mean ⫾ standard deviation) as measured with a Bailey-Lovie25 visual acuity chart.
Change is calculated as letters correct in year 8⫺letters correct at baseline, so a negative number represents a worsening of visual
acuity. Mild, moderate, and severe are denoted by corneal curvature (FDACL of ⬍45 D, 45–52 D, and ⬎52 D, respectively).
nus, visual acuity, contact lens comfort, and NEI-VFQ quality-oflife data, this ⬙natural history⬙ sample cannot determine causal
proof that one method of fitting lenses is safer than another. To
achieve this, a randomized clinical trial is needed.
Clinicians overwhelmingly fit flat. Previous data from the
CLEK Study sample showed that, of the 808 patients wearing rigid
contact lenses in one or both eyes at baseline, 88% were fitted flat
and only 12% were fitted steep.21 The small sample of eyes fitted
steep in the CLEK Study is a severe limitation. The second—and
more confounding—factor is that eyes fitted very flat have more
advanced keratoconus.21,24,26 The linking of advanced disease and
flat fit render it nearly impossible to statistically discriminate between the effect of flat contact lens fit from disease severity on
visual acuity, contact lens comfort, ocular pain, and incident corneal scarring.
These data appear to refute the long-held clinical wisdom that
flat-fitting rigid contact lenses somehow compress the apex of the
cone in keratoconus and provide the patient with better visual
acuity. In previous work applying flat- and steep-fitting lenses to
keratoconic eyes and measuring visual acuity in a single test session
without allowing days to weeks of adaptation to the lenses, Zadnik
and Mutti found that visual acuity was variable and that neither
lens fitting strategy had a clear advantage,27 whereas Sorbara et al
found that the steepest base curve provided the worst visual acuity
compared with flatter lenses and that lenses fitted 0.2 to 0.3 mm
flatter than their subjects’ habitual rigid lenses resulted in the best
vision.28 The data in this article show that eyes with mild to moderate keratoconus wearing steep-fitting lenses tended to have better
visual acuity, on the order of half a line for entrance visual acuity
for high- and low-contrast visual acuity, respectively, and 0.5 to
one line better for best-corrected visual acuity. Thus, the clinician’s
bias toward fitting flat-fitting rigid lenses to improve visual acuity
may be challenged by the data presented here.
Likewise, the assumption that one fitting strategy produces a
rigid contact lens fit that is more or less tolerated by patients is
challenged by these data. In fact, patients report remarkably similar
levels of contact lens-related comfort with their lenses, regardless of
the fitting strategy and wear their lenses an average of 13 hours per
day.
The CLEK Study Group (as of April 2004)
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,
2000 –2001), 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 (Backup Photographer), Janet
Edgerton, COT (Technician), Mark Harrod (Photographer), Patricia
Kane (Backup Photographer), Jonathan H. Lass, MD (Co-Investigator),
Jeffrey C. Lerner (Technician), Dawn McInture (Technician), Kristee
Mines (Backup Study Coordinator), Stephanie M. Shaffer, MA (Study
Coordinator), Thomas Stokkermans, OD, PhD (Co-Investigator), Pamela A. Smith (Technician, 1999 –2002), Kimberly D. Supp (Technician,
1994 –1999), Bonita Darby (Study Coordinator, 1994 –1996), Ellen M.
Stewart (Photographer, 1995–1997), Laura A. Teutsch (Technician,
1995–1999), Kimberly L. Schach (Study Coordinator, 2000 –2002)
Gundersen Lutheran, La Crosse, WI: John L. Sterling, OD (Principal
Investigator), Thomas M. Edwards, OD (Co-Investigator), Lisa J. Feuerhelm (Technician), 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,
Optometry and Vision Science, Vol. 82, No. 12, December 2005
1020
Contact Lens Fitting Methods in Keratoconus—Zadnik et al.
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: Colleen Riley, OD MS (Principal
Investigator), Gerald E. Lowther, OD, PhD (Co-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), Stephanie K. Sim–-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 (CoInvestigator), Ronit Englanoff, OD (Co-Investigator), Elisabeth T. Lim
(Technician), Louis Rosenberg, OD (Co-Investigator), Arti S. Shah, 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), Ivetta S. Siedlecki, 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), Nancy M. Duquette (Study Coordinator, 1995–1998),
Janene R. Sims, OD (Co-Investigator, 2000 –2002)
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 (CoInvestigator), 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 (CoInvestigator, 1995–1996)
Pennsylvania College of Optometry, Philadelphia, PA: Joel A. Silbert, OD
(Principal Investigator), Kenneth M. Daniels, OD (Co-Investigator),
Mary Jameson (Backup Study Coordinator), Theresa E. Sanogo (Study
Coordinator), David T. Gubman, OD, MS (Co-Investigator,
1998 –2000)
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: 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), Kimberley 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), Lanna Blue (Secretary), Jodi M. Malone, RN (Study Coordinator), Jeffrey J. Walline, OD,
PhD (Optometrist), Dione Allen (Secretary, 1997–2000), Nora McFadden (Secretary, 2000 –2002)
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, MS
(Reader, based at Bausch & Lomb), Beth 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), Steven Kymes, PhD (Statistical Data Analyst), Karen Steger-May (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),
Michi Goto (Research Assistant), Cynthia Roberts, PhD (Consultant),
George A. Rosas (Study Coordinator), Loretta B. Szczotka, OD, MS
(Consultant), Mark Wright, MS (Programmer/Analyst), Stephanie K.
Schoepfer-Grosskurth (Reader), Stephanie Walter Cooper (Reader, 1998),
Thomas W. Raasch, OD, PhD (Consultant, 2000 –2002), Dasia Corado
(Reader, 2001)
Project Office, National Eye Institute, Rockville, MD: Donald F.
Everett, MA
Committees
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 (CoChairman), 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
ACKNOWLEDGMENTS
The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is
supported by the National Eye Institute/National Institutes of Health, grants
EY10419, EY10069, EY10077, EY12656, and EY02687. It also was supported by Conforma Contact Lenses, Paragon Vision Sciences, CIBA Vision
Corporation, and the Ohio Lions Eye Research Foundation.
Received May 19, 2005; accepted August 29, 2005.
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Karla Zadnik
The Ohio State University College of Optometry
338 West Tenth Avenue
Columbus, Ohio 43210-1240
e-mail: [email protected]
Optometry and Vision Science, Vol. 82, No. 12, December 2005