Rigid contact lens decentration: a risk factor for corneal warpage

Clinically significant contact lens induced corneal warpage is seen in a small proportion of soft and rigid contact lens wearers. Previous studies using the keratometer have found no correlation between the fit of the lens and the induced topographic changes. In this study, using computer-assisted topographic analysis, seven eyes (four patients) with rigid contact lens-induced corneal warpage were noted to have topographic abnormalities that correlated with the decentered resting position of the contact lens on the cornea. The warpage topography for each of these corneas was characterized by a relative flattening of the cornea underlying the resting position of the contact lens. Lenses that rode high, for example, produced flattening superiorly and resulted in a relatively steeper contour inferiorly that simulated the topography of early keratoconus patients who had not worn contact lenses. After discontinuing contact lenses the corneal topography returned to a normal pattern in five eyes. Two eyes retained asymmetry that is not characteristic of normal corneas. Up to 6 months was required for the corneas to return to a stable topography after contact lens wear was discontinued.     

Same PMMA contact lenses worn for over 30 years: A case report

Many, often asymptomatic, contact lens wearers have alterations of the corneal topography called corneal warpage. These topographic abnormalities are characterized by the presence of irregular astigmatism, loss of radial symmetry, and frequent reversal of the normal topographic pattern of progressive flattening of corneal contour from the center to the periphery. We describe a case in which the same pair of PMMA contact lenses was worn for over 30 years. The patient had no symptoms regarding her contact lenses, but on a visit for a posterior vitreous detachment, we found typical signs of corneal warpage, which resolved after 12 weeks of contact lens wear suspension     

Time to resolution of contact lens-induced corneal warpage prior to refractive surgery.

PURPOSE: To evaluate the resolution of contact lens-induced corneal warpage before keratorefractive surgery. METHODS: We prospectively studied the eyes of 165 consecutive contact lens-wearing patients evaluated for keratorefractive surgery. Significant contact lens-induced corneal warpage was detected by comeal topography in 20 eyes of 11 patients. Manifested refraction, keratometry, and cornea topography were subsequently recorded during weekly or biweekly reevaluations and were compared with previous measurements for stability. Effects of age, sex, type, and duration of contact-lens wear and the recovery time period to stabilization were analyzed. RESULTS: Overall, a 12% incidence of significant contact lens-induced corneal warpage was found. In patients demonstrating lens-associated warpage, the mean duration of prior contact lens wear was 21.2 years (range 10 to 30 years); lens use included daily wear soft (n=2), extended-wear soft (n=6), toric (n=4), and rigid gas-permeable contact lenses (n=8). Up to 3.0 diopter (D) refractive and 2.5D keratometric shifts accompanied by significant topography pattern differences were observed. The average recovery time for stabilization of refraction, keratometry (change within +/- 0.5D), and topography pattern was 7.8+/-6.7 weeks (range 1 to 20 weeks). Recovery rates differed between the lens types: soft extended-wear 11.6+/-8.5 weeks, soft toric lens 5.5+/-4.9 weeks, soft daily wear 2.5+/-2.1 weeks, and rigid gas-permeable 8.8+/-6.8 weeks. CONCLUSION: We observed a 12% incidence of significant contact lens-induced corneal warpage in patients undergoing evaluation for keratorefractive surgery. Warpage occurred with all types of contact lens wear but resolved at different rates. To optimize the quality and predictability of keratorefractive procedures, an appropriate waiting period is necessary for contact lens-induced corneal warpage to stabilize. We suggest that resolution of corneal warpage be documented by stable serial manifested refractions, keratometry, and corneal topographic patterns before scheduling patients for keratorefractive surgery.     

Differentiating contact lens induced warpage from true keratoconus using corneal topography.

PURPOSE: Superior corneal flattening associated with inferior corneal steepening is a videokeratoscopic topography pattern that usually describes both keratoconus and contact lens induced warpage. To differentiate these two conditions topographically, we analyzed ten different corneal topographic shape variables and found that two distinct conditions were described. Three unique measurements of corneal geometry: shape factor (SF), irregularity (CIM), and apical toricity (TKM) were analyzed and evaluated as an additional method for differentiating these two conditions. METHODS: A retrospective series of 100 eyes with a medical diagnosis of either contact lens induced warpage or true keratoconus were mapped using the Humphrey Atlas Corneal Topographer (San Leandro, CA) and their individual topographic indices were analyzed in an attempt differentiate the two conditions with videokeratoscopy. Variables included Flat Keratometry Reading, Maximum Axial Curvature, Maximum Tangential Curvature, Corneal Astigmatism, Corneal Shape Factor, Reference Sphere, Corneal Irregularity Measure (CIM), Maximum Elevation, and Mean Reference Toric K (TKM). All patients wore rigid gas permeable contact lenses. RESULTS: True keratoconic eyes had steeperflat K readings (46.9+/-3.7 D vs. 43.04+/-1.18 D; P<6.3E-13) with greater variations in maximum axial curvature (54.1+/-4.76 D vs. 43.6+/-1.5 D; P<2.4E-15) and maximum tangential curvature (55.1 7+/-4.56 D vs. 47.7+/-1.5 D; P<5.4E-16) than did eyes with contact lens induced warpage. The amount of corneal toricity (-3.43+/-2.29 D vs. -1.33+/-0.88 D; P<1.5E-07) was also greater for true keratoconus. True keratoconic eyes had larger and more variable shape factors (0.61+/-0.26 vs. 0.02+/-0.13; P<2.5E-19) and CIM's (2.30+/-1.16 vs. 1.03+/-0.37; P<7.5E-10) than those with contact lens induced warpage. Steeper reference spheres (47.58+/-3.55 D vs. 43.6+/-0.37 D; P<2.2E-10), greater maximum elevation over their respective reference spheres (15.51+/-9.91 microns vs. 6.2+/-3.0 microns; P<8.1E-08) and steeper, more variable toric mean reference spheres (51.88+/-4.01 D vs. 43.82+/-1.82 D; P<3.9E-17) are also present in true keratocon us. True keratoconic eyes can be separated from contact lens induced warpage eyes with a sensitivity of 98%, while identification of contact lens induced warpage demonstrates 94% specificity using corneal topography. CONCLUSIONS: While contact lens induced warpage and true keratoconus exhibit similar corneal topography patterns (superior flattening and inferior steepening), they demonstrate two uniquely different geometric shapes that can be readily differentiated using the various corneal shape indices of videokeratoscopy with a high degree of accuracy and specificity.     

Predicting time to refractive stability after discontinuation of rigid contact lens wear before refractive surgery

PURPOSE: To determine whether discontinuing rigid contact lenses for 3 weeks is sufficient to achieve refractive stability and if not, to identify factors, including indicators of corneal warpage, that are associated with prolonged corneal instability. SETTING: University-based refractive surgery practice. METHODS: Charts of patients seen for refractive surgery consultation from January 1999 to March 2001 were reviewed. Patients with a history of rigid gas-permeable (RGP) contact lens use were identified and instructed to discontinue wearing lenses 3 weeks before the initial examination. Patients were examined at 3-week intervals until a stable refraction was achieved (within +/-0.25 diopter [D] sphere and 0.25 D cylinder with less than 25 degrees of axis orientation). Visual acuity, subjective refraction, and corneal topography were obtained at each visit. RESULTS: Of 55 eyes of 28 patients, 31 eyes achieved refractive stability by the second visit (early-stability group) and 24 eyes required more than 2 visits to achieve stability (late-stability group). No statistically significant between-group difference was observed in age, sex, refractive cylinder, topographic cylinder, difference between refractive and topographic cylinders, surface regularity index, surface asymmetry index, or spherical equivalent at the initial examination. The number of years of contact lens wear was significantly different between the groups (P = .05). CONCLUSIONS: The time for contact lens-induced corneal changes to reach a steady state after cessation of lens wear is highly variable. Among the variables examined, including those indicating corneal warpage, the factor that correlated with the required time to refractive stability after discontinuation of RGP wear was the length of time of contact lens use. Patients who are long-term RGP wearers should be counseled that multiple visits will likely be required before a stable refraction is obtained.     

The relationship between long-term contact lens wear and corneal thickness.

PURPOSE: The purpose of this study is to assess the effects of long-term contact lens wear on corneal thickness and to compare differences based on rigid versus soft lens material. METHODS: This analysis included scanning slit topographic imaging (Orbscan, Bausch & Lomb, Rochester, NY) performed on 124 consecutive patients (248 eyes), who underwent comprehensive evaluations in consideration of refractive surgery by one surgeon. RESULTS: Sixty-two 62 patients (124 eyes) who had not previously worn contact lenses had a least-squares mean pachymetry of 546.4 microm +/-3.5 SE. Thirty-nine patients (78 eyes) who had previously worn soft contact lenses for an average of 16 years had a least-squares mean pachymetry of 543.2 microm +/-3.8 SE. Twenty-three patients (46 eyes) who had worn rigid contact lenses for an average of 19 years had a least-squares mean pachymetry of 509.4 microm +/-6.9 SE. Mean pachymetry differed significantly between eyes wearing rigid lenses versus no lenses (P<0.0001) and between eyes wearing rigid lenses versus soft lenses (P=0.0002). CONCLUSION: Long-term rigid contact lens wear is associated with a decrease in the average central-corneal thickness (CCT) by an average of 37 microm, in this group of otherwise healthy eyes, compared to no contact lens wear. Long-term soft contact lens wear did not appear to significantly change corneal thickness compared to no contact lens wear. Caution should be exercised when screening patients with a history of long-term rigid contact lens wear for possible excimer-laser photoablative correction.     

Is abnormal focal steepening of the cornea related to persistent monocular diplopia?

PURPOSE: Some case reports have shown that abnormal focal steepening of the cornea appears to cause monocular diplopia by prismatic effect. The purpose of this study was to ascertain prospectively if the pattern of corneal distortion was related specifically to persistent monocular diplopia. METHODS: We selected 16 visually normal eyes (controls) and two groups of volunteers in which abnormal focal steepening of the cornea was expected to be found: 40 eyes of 20 volunteers who wore rigid gas-permeable contact lenses (RGP) for myopia and 10 eyes of seven patients with keratoconus. New charts that consisted of white dials on a black background were prepared for detection and measurement of secondary images. Any secondary image that could not be eliminated by any trial lens correction was defined as a persistent secondary image, using the charts. Corneal topography from all subjects was classified: round or oval, symmetric or asymmetric bowtie, abnormal focal steepening accompanied by contact lens-induced corneal warpage or keratoconus, or amorphous. We analyzed the relationship between the persistent secondary image and the corneal topographical patterns. RESULTS: A persistent secondary image was detected from seven eyes of RGP wearers and all keratoconus eyes. All corneal topographies of the seven RGP eyes with a persistent secondary image showed abnormal focal steepening related to contact lens-induced corneal warpage. The direction of the persistent secondary image was approximately consistent with the location of the focal steepening as seen on the corneal topography. CONCLUSION: Abnormal focal steepening of the cornea that appeared to produce a prismatic difference between two parts of the cornea was specifically related to persistent monocular diplopia.     

Contact lens selection for keratoconus using a computer-assisted videophotokeratoscope

We used the Corneal Modeling System, a digital videophotokeratoscope, as an aid in selecting the initial base curve and lens diameter for contact lenses in keratoconus patients. With this instrument we studied corneal topography in 24 keratoconus patients (33 eyes) who were being fit for the first time or who had not worn contact lenses for at least one month prior to our examination. For the purposes of fitting contact lenses, the corneas were classified according to the topographic patterns observed, and appropriate fitting strategies were adopted for each subgroup. Diagnostic lenses and their fluorescein patterns were analyzed for the desired cornea-lens relationship. Topographic analysis of the cornea provided a rational basis for selecting appropriate trial contact lenses for our patients.     

Swelling and deswelling of rabbit corneas in response to rigid gas permeable, hydrogel and elastomer contact lens wear

We determined diurnal variation in corneal thickness in rabbits prior to and following overnight wear of: (i) selected rigid contact lenses with different Dk values; (ii) hydrogel lenses of low and high water content; and (iii) elastomer lenses. The degree of contact lens-induced corneal swelling observed during 24 hours of lens wear, and the rates of deswelling in the subsequent 24 hours, correlated well with the different oxygen transmissibilities of the individual RGP contact lenses. The greatest swelling (21.6 +/- 5.4%) followed the wear of PMMA lenses. The least swelling, 2.9 +/- 4.0%, followed the wear of rigid gas permeable (RGP) Menicon SF-P (melafocon A) lenses, a value nearly identical to the swelling observed in the morning following sleep without lenses, (0.0 +/- 3.1%). By contrast, low-water content hydrogel soft contact lens use was associated with drastic corneal deswelling rates (-15.1 +/- 4.5%) during the hours after lens wear. The difference between these and control corneas was significant by paired t-test (P less than 0.01). Eyes wearing high water content lenses had less deswelling than eyes with their low-water counterparts. Corneal swelling produced by elastomer lenses was similar to that seen with RGP lenses.     

Contact lens manipulation of corneal topography after penetrating keratoplasty: a preliminary study.

We conducted a preliminary retrospective study of five eyes that had undergone penetrating keratoplasty (PK) to determine if rigid gas permeable (RGP) contact lenses could be used as splints or molds to improve postoperative corneal topography. RGP lenses were fit 3-6 months (mean: 4.1 months) after PK and 3-4 months (mean: 1.8 months) after removal of the 10-0 nylon suture. Lenses were fit to attain a contact lens resting position centered on the corneal graft. After 4 to 8 months (mean: 6.2 months) of contact lens wear, analysis of corneal topography showed a decrease in simulated keratometry cylinder from 4.7 +/- 0.6 D (mean +/- 1 standard deviation) to 1.8 +/- 0.8 D (P = 0.02) and an improvement in anterior corneal surface regularity (surface regularity index: initial = 1.40 +/- 0.2; final = 1.0 +/- 0.2; P = 0.04). Three eyes were fit with a well-centered RGP lens; two eyes were fit with lenses that rode off-center. Increased irregular astigmatism in the two eyes with decentered contact lenses suggests the importance of centering RGP lenses with respect to corneal grafts. The best corrected spectacle visual acuity either improved or remained unchanged in four of five eyes after contact lens wear. One eye demonstrated a decrease in best corrected spectacle acuity by one Snellen line after 3 months of lens wear. Further clinical studies are needed to determine the potential of postoperative use of RGP lenses to improve corneal surface regularity, to decrease astigmatism, and to optimize visual results.     

Rigid contact lens fitting relationships in keratoconus. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group.

PURPOSE: Although the influence of flat-fitting contact lenses on corneal scarring in keratoconus is frequently debated, the current standard of care with regard to the apical fitting relationship in keratoconus remains undocumented. METHODS: Patients were examined at baseline in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study (N = 1209). Patients wearing a rigid contact lens in one or both eyes (N = 808) had their habitual rigid contact lenses analyzed, and the fluorescein patterns and base curves were compared to the first definite apical clearance lens (FDACL). The FDACL is the flattest lens in the CLEK Study trial lens set that exhibits an apical clearance fluorescein pattern. For patients wearing a rigid contact lens in both eyes, one eye was selected randomly for analysis. RESULTS: Twelve percent of the rigid contact lens-wearing eyes were wearing lenses fitted with apical clearance based upon the clinician's fluorescein pattern interpretation. The remainder (88%) was wearing lenses fitted with apical touch. For mild (steep keratometric reading <45 D) keratoconus corneas, the mean estimate of the base curve to cornea-fitting relationship was 1.18 D flat (SD +/- 1.84 D); moderate (steep keratometric reading: 45 to 52 D) corneas were fitted on average 2.38 D flat (SD +/- 2.56 D); and severe (steep keratometric reading > 52 D) corneas were fitted an average of 4.01 D flat (SD +/- 4.11 D). CONCLUSIONS: Despite the potential risk for corneal scarring imposed by flat-fitting rigid contact lenses, most CLEK Study patients wear flat-fitting lenses. Overall, rigid lenses were fitted an average of 2.86 D (SD +/- 3.31 D) flatter than the FDACL.     

Rigid gas-permeable contact lenses for myopia control: effects of discontinuation of lens wear

Conventionally fitted Paraperm O2plus contact lenses were worn for 44 months by 23 myopic children, who discontinued lens wear for 2.5 months and then resumed lens wear with Fluoroperm 30 lenses for a period of 8 months. Mean changes in myopia were: (1) an increase of 0.76 D during the initial 44 months of lens wear, (2) a further increase of 0.27 D during the 2.5 months when lenses were not worn, and (3) a decrease of 0.02 D during the 8-month period of Fluoroperm 30 lens wear. These results show that the effect of rigid gas-permeable lenses on myopia progression is diminished if lens wear is discontinued; however, the mean increase in myopia for these children was significantly less than would have been expected if glasses had been worn for the entire 54.5-month period. The results after discontinuation and then resumption of lens wear show that the effect of contact lenses in controlling the progression of myopia could not be accounted for entirely on the basis of corneal flattening as measured by the keratometer, therefore reinforcing the conclusion that corneal flattening due to rigid lens wear takes place primarily at the corneal apex, rather than in the zone of the cornea measured by the keratometer.     

Effect of softperm lens wear on corneal thickness and topography: a comparison between keratoconic and normal corneae.

PURPOSE: Complications related to contact lens-induced anoxia in the keratoconic eye are well documented, but the underlying mechanisms are poorly understood. This study compared topographical changes in corneal thickness and anterior corneal radius following SoftPerm (Ciba Vision, Atlanta, GA) (rigid-and-soft combination) lens wear in a group of keratoconic and normal individuals. METHODS: Video keratoscopic (VKS) (EyeSys, Houston, TX) and ultrasonographic pachometry measurements were taken at nine ocular locations, at central, mid-peripheral, and peripheral corneal areas of keratoconic and normal subjects. Subjects were subsequently fitted with SoftPerm lenses and further measurements of corneal topography and thickness were noted after 1 day, 2 weeks, and 1 month of daily wear. RESULTS: Corneal thickness increased significantly in normal and keratoconic eyes following SoftPerm lens wear. Radius values obtained from the VKS measurements indicated that a significant and progressive degree of corneal flattening occurred for the keratoconic subjects at the 1-day, 2-week, and 1-month intervals, in contrast to the normal group, whose corneal radii remained unchanged. CONCLUSIONS: Corneal swelling occurs in both normal and keratoconic corneas following SoftPerm lens wear. Differences in the apparent central edema response within the keratoconic group may relate to the ease with which these corneas may be molded by a rigid contact lens.     

The effects of wearing the Boston II gas-permeable contact lens on central corneal curvature

Keratometric readings on 132 different eyes were examined from the patient records. Sixty eyes had previously worn polymethyl methacrylate (PMMA) lenses and then were refitted with the Boston II gas-permeable contact lens. The remaining 72 eyes had never worn contact lenses and these too were fitted with the Boston II lens. The Boston II contact lens is a nonhydrophilic contact lens composed of methylmethacrylate-dimethylitaconate-siloxanyl copolymer with a reported Dk value of 14.6 X 10(-11) ml O2 cm2/s ml mm Hg (35 degrees C). The mean and SD of the keratometric readings and the amount of corneal toricity found were calculated for each set of progress reports. The data in this study indicate that an alignment-fitting Boston II gas-permeable contact lens does not cause curvature changes in corneas during the first three months of wear.     

正常戴角膜接触镜患者的角膜地形图变化

通过对戴角膜接触镜患者停镜后进行定期角膜地形图观察，发现戴角膜接触镜可引起角膜变形，如中心区不规则散光、缺乏正常角膜的由中心向周围逐渐变扁平和丧失辐射性对称。停镜后角膜恢复正常形态的时间为2～8周，平均为4．07±1．76周。最长时间为12周。停镜2周左右角膜变化较明显。提示屈光性角膜手术前，对戴角膜接触镜患者要定期检查角膜地形图，直至角膜形态恢复正常，才可进行手术治疗。     

Rigid gas permeable contact lenses fitted in a case of congenital glaucoma

CASE REPORT: A 27-year-old woman with congenital glaucoma with high myopia, low visual acuity and nystagmus in both eyes, was referred for contact lens fitting. We fitted her with aspherical rigid gas permeable (RGP) contact lenses with high transmissibility, which she wore on a daily basis. Her visual acuity improved with the wearing of these lenses, which remained comfortable whilst being worn for 10 hours a day. DISCUSSION: Contact lenses were fitted according to her corneal topography. Gas permeable contact lenses were chosen as first choice and with proper fitting and vigilant follow-up they may be worn safely on a daily basis.     

Contact lenses and corneal deformation: cause, correlate or co-incidence?

Sporadic reports describing cases of corneal deformation (i.e. corneal warpage with astigmatism or keratoconus) after a minimum of about 4 years contact lens wear are condensed into Table 1. Some severe cases required corneal grafting. Eight personal cases are described in Table 2, including two who have worn only soft lenses and one who has worn soft lenses for 6 out of 7 years. It is suggested that although some cases of this corneal distortion might well have occurred without contact lenses, the trauma of years of contact lens wear is causative if the individual's cornea is predisposed, possibly by the carrier state of hereditary naturally-occurring keratoconus. A risk-averse patient and practitioner would probably add this to other possible complications, and restrict contact lenses to eyes with more severe refractive errors, and minimise the wearing time.     

The Dundee University Scottish Keratoconus Study II: a prospective study of optical and surgical correction

AIM: To investigate and correlate optical correction, and progression to penetrating keratoplasty (PKP), with the corneal, refractive, topographic and familial characteristics of subjects with keratoconus, within the Tayside region of Scotland. METHOD: Prospective, observational, longitudinal study design. Two hundred subjects with keratoconus were enrolled into the Dundee University Scottish Keratoconus Study (DUSKS) and were assessed during a 4-year period using standardised clinical assessment, computerised corneal topography and questionnaires. RESULTS: Keratoconic subjects in this study wore rigid contact lenses (90.6%) for longer than 12 hours per day (81%), 7 days a week (91%) and achieved a very good level of Snellen visual acuity (97%, > or =6/9). Corneal staining was observed in the majority of corneas (71%), although only a small percentage of subjects reported major problems of: discomfort (18%), hyperaemia (16%), or the lens falling out (4%). Poor visual acuity was the main reason (79%) for undergoing PKP usually in the latter part of the third decade of life, approximately a decade after diagnosis. During the study period 4% of eyes progressed to PKP. Only a small percentage of eyes (9.5%) required no visual correction postoperatively. CONCLUSION: The main mode of visual rehabilitation for keratoconus was rigid contact lenses, which were mostly worn successfully with good visual acuity. During the study period a small minority of keratoconics progressed to corneal graft surgery. It is advisable to emphasise that postoperatively refractive correction will be required in the majority of these cases.     

Irregular astigmatism after radial and astigmatic keratotomy

Eleven eyes of six patients, who had been referred for management of irregular astigmatism after receiving crossed incisions for myopic astigmatism, had moderate to marked irregular corneal astigmatism with marked flattening in the meridians of intersecting incisions. All six patients had a decrease in best-corrected visual acuity with spectacles after surgery. Visual acuity with spectacles was 20/40 in five of 11 eyes; with contact lenses it reached 20/40 in ten of 11 eyes. However, two patients could not wear the contact lenses because of lens decentration caused by the marked distortion in corneal topography. Even with contact lenses, visual acuity could only be improved to 20/25 or better in six of 11 eyes.     

Comparison of flat and steep rigid contact lens fitting methods in keratoconus.

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 = 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,= 2.19; 95% CI, 1.37-3.51; p = 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 = 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 = 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.