Contact lens fitting after corneal collagen cross-linking.

BACKGROUND: Contact lenses (CLs) remain the mainstay in improving vision in patients having keratoconus. With corneal collagen cross-linking (CXL) performed worldwide, whether the same CLs can be used or needs replacement needed to be assessed and considered. AIMS: The aim of this study was to evaluate the changes in CL fitting following CXL. SETTINGS AND
DESIGN: This is a retrospective study conducted at a tertiary center. SUBJECTS AND METHODS: We analyzed the medical records of patients who underwent CXL and used CL. Data collected included demographics, pre- and post-CXL refraction, corneal topography, anterior-segment examination, and CL [rigid gas permeable(RGP)] fitting details and duration between CXL and RGP fitting. STATISTICAL ANALYSIS: Descriptive analysis and paired t-test were used to compare the pre- and post-CXL data on refraction, visual acuity, and CL parameters. The statistical significance was kept at P < 0.05.
RESULTS: Thirty-four eyes (keratoconus = 32, pellucid marginal degeneration = 1, and post-LASIK ectasia = 1) of 27 patients who used CL before and after undergoing CXL were analyzed. Mean duration between CXL and RGP lens use was 2.53 months. Mean sphere and cylinder post-CXL was -4.11 ± 4.32 D and -3.54 ± 2.51 D, respectively. A mean change of 0.75 ± 3.72 D sphere and 0.71 ± 3.39 D cylinder was noted post-CXL. The post-CXL best spectacle-corrected visual acuity (CVA) was 0.52 ± 0.36 and with RGP lens it was 0.09 ± 0.18. There was no significant difference in pre- and post-CXL RGP lens CVA (0.07 ± 0.09 and 0.09 ± 0.18, respectively; P = 0.556). Pre-CXL, 3-point-touch fitting was in 24 eyes (70.59%) and central fluorescein pooling was in 10 eyes (29.41%). Post-CXL, 30 eyes (88.24%) had 3-point-touch and central fluorescein pooling was found in four eyes (11.76%). One patient had CL intolerance after CXL. Of the 32 keratoconus eyes, 62.5% (n = 20 eyes) were prescribed new lenses; 37.5% (n = 12 eyes) continued using own lenses.
CONCLUSIONS: There was no significant difference in refraction, topography indices, and RGP lens parameters pre- and post-CXL. However, changes in RGP lens fitting characteristics suggest a possible change in shape or apex location of the cornea after CXL. RGP lenses remain the best option to improve visual acuity after CXL in corneal ectasia. Copyright:

Introduction

Keratoconus is a bilateral, progressive, asymmetric, noninflammatory ectatic disorder of the cornea that results in high irregular astigmatism leading to reduced vision. The incidence of keratoconus is 1 in 2000 among the general population.[1] Currently, the options available to improve vision are either nonsurgical such as spectacles and contact lenses (CLs) or surgical such as intracorneal rings, photorefractive keratectomy, and keratoplasty.[234] All these procedures are for refractive correction and do not arrest the progression of keratoconus. Wollensak et al. had shown the effectiveness of corneal collagen cross-linking (CXL) with the help of ultraviolet A and the photosensitizer riboflavin to arrest the progression of keratoconus and “freeze” the cornea.[56] Flattening of the central corneal curvature, improvement in the best-corrected visual acuity (CVA), reduction in the corneal higher order, and astigmatic wavefront aberrations were reported after CXL in keratoconus eyes.[5789]

Rigid gas-permeable (RGP) CLs are a good option for improving vision in keratoconic eyes.[410111213] The selections of RGP CL parameters are mainly dependent on the severity and morphology of the cone.[14] Corneal topography is an important tool that may help in determining the severity and morphology of the cone. There are various reports on the selection of CL base curve and diameter based on different corneal topography indices in keratoconus eyes.[21415] There are reports on the changes of corneal curvature and other corneal topography indices with CXL.[9161718] CL use after CXL is reported in the literature.[181920] The aim of the current study is to evaluate the rigid CL fitting following CXL.

Subjects and Methods

Medical records of patients who underwent CXL and presented to Contact Lens Clinic from January 2008 to July 2011 were reviewed. This is a retrospective-observational study.

All these patients had comprehensive ocular examination and topography measurement using Orbscan IIz (Bausch and Lomb, Rochester, NY) before and after cross-linking. Patients who had pre- and post-surgical RGP CL usage were included in the study. Those who discontinued CL wear after surgery were excluded from the study. All patients underwent a diagnostic CL-fitting method based on the corneal topography data. The CL trial was repeated until an acceptable dynamic and static fit was achieved. The dynamic fit was considered as acceptable if the lens centered well on the cornea, with postblink movement of 1.5–2.0 mm and stable in all directions of gaze movements. In the static fit assessment with the application of fluorescein, the CL fit was considered acceptable if there was a minimal central clearance to minimal central bearing and edge clearance of 0.4–0.6 mm. Once the lens fit was found to be acceptable with the trial lens, overrefraction was performed to finalize the CL power. The data collected included the patient demographics, pre- and post-surgical refraction, corneal topography, anterior-segment examination, and CL details and the duration between the surgery and CL fitting.

Statistical analysis

Shapiro–Wilk test was used to check the normality of data and the P value was not significant. Descriptive analysis was used to describe patient demograxsphics, and paired t-test was used to compare the pre- and post-CXL data on refraction, visual acuity, CL parameters of base curve and power, and the minimum and maximum Sim K values. The statistical significance was kept at P < 0.05. Snellen visual acuity was converted to LogMAR visual acuity for statistical analysis.

Results

Thirty-four eyes of 27 patients were included in the study. Among them, 23 were males and 11 were females. The mean age was 19.4 ± 4.3 years (range: 11–26 years). Thirty-two eyes had keratoconus; pellucid marginal degeneration and post-LASIK ectasia were noted in one eye each. One patient had keratoconus associated with vernal keratoconjunctivitis. Among the keratoconic eyes, 19 eyes had Vogt's striae, 27 eyes had Fleischer's ring, and seven had apical scar preoperatively. Of these 32 eyes, five eyes had Stage I disease (Amsler–Krumeich classification), 13 had Stage II, three had Stage III, and 11 had Stage IV disease.

Table 1 shows the pre- and post-operative refraction, corneal topography, and CL parameters.

Table 1

Pre- and post-operative data

Variables	Preoperative	Postoperative	P
Refraction_ sphere	−4.16±4.77	−4.11±4.32	0.278
Refraction_cyl	−4.36±3.16	−3.54±2.51	0.261
Best spectacle-CVA	0.50±0.37	0.52±0.36	0.751
Sim K _max	56.12±5.44	57.31±4.87	0.233
Sim K_min	50.26±4.64	51.4±5.05	0.099
Contact lens _BC	6.99±0.41	6.92±0.38	0.103
Contact lens_Power	−5.15±2.86	−5.63±3.03	0.133
Contact lens_CVA	0.07±0.09	0.09±0.18	0.556
Average CL-wearing period (hours/day)	10.31±1.35	10.25±2.01	0.884

CL: Contact lens, BC: Base curve, CVA: Corrected visual acuity

The mean duration between the surgery and CL use was 2.53 months (range: 1–5 months). Preoperatively in 24 eyes (70.59%), the CL fit was found to be 3-point touch [Figure 1] and in 10 eyes (29.41%), the CL fit exhibited central fluorescein pooling. Inferior-edge lift was noticed in three eyes. The mean daily wearing time was 10.36 ± 2.40 h.

Figure 1

3-point-touch type of fitting of rigid gas-permeable lens before corneal cross-linking

Thirty-one eyes (91.17%) had developed central corneal haze following corneal CXL. After the CXL, the type of CL prescribed was not changed and 20 eyes continued with RGP lens and 14 eyes with Rose K lenses. The type of CL fit achieved after CXL was 3-point-touch in thirty eyes (88.24%) and central fluorescein pooling in four eyes (11.76%) [Figure 2]. Only one patient developed CL intolerance following CXL, and the rest of the patients were comfortable with CL wear with an average wearing period of 10.25 ± 2.01 h per day after CXL. In keratoconus patients, 12 patients continued to wear the same lenses and 20 patients had their lenses changed.

Figure 2

The same patient of Figure 1 showing pooling of fluorescein with rigid gas-permeable lens after corneal cross-linking as seen using Wratten filter

Table 2 shows the parameters of the same lenses used versus change of lens parameter after CXL.

Table 2

Parameters of same and different lenses before and after corneal collagen cross-linking

	Different lenses (n=20)		Same lenses (n=12)
	Pre-CXL	Post-CXL	Pre-CXL	Post-CXL
Sim K Flat	49.47±4.75	51.43±5.05	51.63±4.37	52.6±4.88
Steep Sim K	57.12±5.83	57.31±4.31	55.85±4.95	56.49±4.46
Base curve	7.00±0.41	6.88±0.35	6.97±0.42
Diameter	9.18±0.48	9.18±0.47	9.07±0.35
Visual acuity	0.06±0.09	0.05±0.07	0.09±0.09	0.09±0.09
Three-point touch	13	18	9	10
Central pooling	7	2	3	2
CL power	−5.44±2.9	−6.16±2.9	−4.52	−2.9

CXL: Corneal cross-linking

Discussion

The major challenges in the management of keratoconus are to improve vision and arrest the progression of the disease. Many studies have shown that CXL is a promising procedure to halt the progression of corneal ectasia. However, this ectasia is arrested in the preexisting shape of the cornea and patients would still have astigmatism. Hence, RGP CL remains the best option to improve the visual acuity in these eyes even after the procedure as seen in this study.

Contrary to the earlier reports,[816] we could not find any significant change in the refractive error, visual acuity, and corneal topography indices after CXL in our series. Though a reduction in astigmatism after the CXL was evident from Table 1, it was not statistically significant. We have included only those patients who had worn CLs prior to surgery and continued CL wear even after surgery. However, there could be patients who experienced improvement in best spectacle-CVA and discontinued CL wear after CXL. As the aim of our study was to report the CL fitting after CXL, we did not include those patients who discontinued CL wear after surgery. In addition, most of the studies reported long-term effect of CXL, minimum follow-up period being 6 months–1 year, whereas, in this study, the average time period between surgery and CL fitting was 2.53 months. Koppen et al. showed the effect of CL wear in improving the shape of keratoconus eyes.[21] In their study, they could demonstrate the architectural molding of the cornea into more regular shape in eyes that fitted with CL shortly after CXL compared to eyes that did not receive any CL.[21] In this study, post-CXL corneal topography and refraction data were obtained before starting CL wear. While the type of CL fitted remained the same even after the procedure, the central fitting had changed in 12 (35.30%) eyes. Among them, change from central pooling to 3-point-touch was seen in nine eyes and from 3-point-touch to central pooling was seen in three eyes (P = 0.146). The change in the CL fit indicates the changes in the shape of the cone after CXL. This is in accordance with the study by Caporossi et al. who had shown an improvement in the morphological symmetry of the cornea and significant reduction in aberrations such as coma after CXL.[22] Though it is possible that the CL wear after CXL could actually result in corneal molding, we have not looked at this effect after CL wear in these eyes. The postrefraction spherical and cylinder values were reduced in this study. This is similar to the study by Singh et al. who have shown reduction in spherical and cylinder values in their study.[18] However, the mean postrefraction CL power is higher – this may be due to the steeper base curve post-CXL compared to preoperative base curve. The daily mean awake wearing time in this study was 10.36 h as against 8 h/day as reported by Singh et al. in their study.[18] Although the corneal sensations are reduced following CXL as reported in the literature, one patient developed CL intolerance in this study.[23]

Though a significant number of eyes in our series developed corneal haze after CXL, there was no significant difference in the visual outcome with CL fitting in these eyes. This is in accordance with the report by Greenstein et al. where they could not find any correlation between the corneal haze and clinical outcome after CXL.[24]

Conclusion

This study describes the RGP CL fitting following CXL and results show that RGP CL can be fitted in these eyes immediately after the healing of the cornea. As evident from this study, one could use patients' own RGP CL or similar parameter lens in the absence of significant changes in the corneal topography. Though the CL parameters remain the same, we could expect some changes in the cornea–CL-fitting relationship due to the possible change in the shape and location of the cone apex and that should be explored further in detail.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.