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Journal Français d'Ophtalmologie
Volume 40, n° 7
pages 535-541 (septembre 2017)
Doi : 10.1016/j.jfo.2017.03.003
Received : 8 November 2016 ;  accepted : 27 Mars 2017
Results at 7years after cross-linking procedure in keratoconic patients
Les résultats à 7 ans après la procédure de réticulation chez les patients atteints de kératocône
 

C. Nicula a, b, c, D. Nicula c, R.N. Pop c,
a Cluj-Napoca University Ophthalmology Clinic, Cluj County Hospital, No. 3-5, Clinicilor Street, 400006 Cluj-Napoca, Romania 
b Iuliu Hațieganu University of Medicine and Pharmacy, Faculty of Medicine, No. 4, Louis Pasteur Street, 400349 Cluj-Napoca, Romania 
c OCULENS Ophthalmology Private Clinic, No. 7, Nicolae Pascaly Street, 400431 Cluj-Napoca, Romania 

Corresponding author. OCULENS Ophthalmology Private Clinic, No. 7, Nicolae Pascaly Street, 400431 Cluj-Napoca, Romania.
Summary
Purpose

Long-term evaluation of functional results based on visual acuity, keratometry, spherical equivalent and refractive cylinder in patients with progressive keratoconus treated with corneal collagen cross-linking (CXL).

Materials and methods

We studied a group of 114 eyes of 91 consecutive patients treated from 2006 to 2009 by “Epi-off type” CXL. In the preoperative period, all patients had a complete ophthalmologic examination. The inclusion criteria were: patients aged 15 to 54years, with various stages of keratoconus, with a corneal thickness of at least 400μm at the thinnest point. The exclusion criteria were: patients with a corneal thickness of less than 400μm at the thinnest point, with Vogt's striae or herpetic keratitis, dry eye syndrome or aphakia. The patients were then followed at 1, 3 and 6months, and then every year between 1 and 7years postoperatively.

Results

There was a decrease in the minimum K and maximum K , respectively 1.6 and 2.0, at 7years postop. (P <0.05). The cylinder decreased from –4.45 D to –3.50 D at 7 years postop (P <0.05). The spherical equivalent decreased by 1.66 D at 7 years (P <0.05). Uncorrected visual acuity increased from an average of 0.78 to 0.679 log MAR (P <0.05) at 7 years postop. The best-corrected visual acuity increased from a mean of 0.64 to 0.52 log Mar (P <0.05) at 7 years postop.

Conclusions

The results of CXL were stable at 7 years in all patients, consisting of reduction of keratometric values and refraction, and improvement in visual acuity.

The full text of this article is available in PDF format.
Résumé
Objectif

Évaluer sur le long terme les résultats fonctionnels, basés sur l’acuité visuelle, la kératométrie, l’équivalent sphérique et le cylindrique réfractif, chez les patients porteurs d’un kératocône évolutif traités par la photo-réticulation du collagène cornéen (CXL).

Matériel et méthode

Nous avons étudié un groupe de 114 yeux de 91 patients consécutifs traités de 2006 à 2009 par CXL de type « Epi-off ». En préopératoire, tous les patients avaient bénéficié d’un examen ophtalmologique complet. Les critères d’inclusion étaient : patients âgés de 15 à 54ans, présentant différents stades de kératocône et dont l’épaisseur de la cornée était d’au moins 400μm au point le plus fin. Les critères d’exclusion étaient les suivants : les patients ayant une épaisseur de la cornée de moins de 400μm au point le plus fin, présentant des stries de Vogt ou une kératite herpétique, un syndrome de l’œil sec ou une aphakie. Les patients ont ensuite été suivis à 1, 3 et 6 mois, puis tous les ans entre 1 et 7 ans postopératoire.

Resultats

Il fut observé une baisse du K minimum et du K maximal, respectivement de 1.6 et de 2.0, à 7 ans postopératoire (p <0,05). Le cylindre avait diminué de –4.45 D à –3.50 D à 7 ans postopératoire (p <0,05). L’équivalent sphérique était abaissé de 1,66 D à 7 ans (p <0,05). L’acuité visuelle non corrigée avait augmenté, d’une moyenne de 0,78 à 0,679 log MAR (p <0,05) à 7 ans postopératoire. La meilleure acuité visuelle corrigée avait augmenté d’une moyenne de 0,64 à 0,52 log Mar (p <0,05) à 7 ans postopératoire.

Conclusions

Les résultats du CXL furent stables à 7 ans chez tous les patients, consistant en la réduction des valeurs kératométriques, de la réfraction et en l’amélioration de l’acuité visuelle.

The full text of this article is available in PDF format.

Keywords : Corneal cross-linking, Decrease, Keratometry, Spherical equivalent, Cylinder

Mots clés : Réticulation cornéenne, Diminution, Kératométrie, Équivalent sphérique, Cylindre


Introduction

Keratoconus (KCN) is a progressive degenerative disease of the cornea, usually bilateral, but most of times asymmetric [1]. In most of the cases, it affects young patients, and an early age of onset is a negative prognostic factor for corneal transplantation [2]. There are several treatment options available, depending on the stage of KCN.

A major breakthrough in blocking the progression of the ectasia is the corneal collagen cross-linking procedure with riboflavin and ultraviolet A (UVA) light [3, 4].

Corneal collagen cross-linking (CXL) means photo polymerization of the stromal fibrillar tissue, in order to increase their stiffness and resistance to the corneal ectasia, through the combined action of the photosensitizing substance (riboflavin–B2) with the irradiation of the ultraviolet A light (UVA), performed with an illuminator in a solid state of UVA kind.

The final effect of CXL technique is the strengthening of the cornea and the goal of CXL is to slow down or arrest the progression of keratoconus avoiding, or at least delaying the necessity of keratoplasty.

In cases of KCN where the patient can correct visual acuity and the corneal thickness allows it, the procedure can be combined with intra-stromal ring implantation in order to flatten the corneal apex, reduce sphericity and also strengthen the cornea.

We chose to apply the transephitelial “epi-off” procedure because the riboflavin penetrates the cornea at about 300 microns when the “epi-on” technique penetrates only at about 150 microns.

Paper purpose

To evaluate functional results based on K measurements, spherical and cylinder equivalent at patients with keratoconus treated with cross-linking, at 1, 3 and 6 months and at 1, 2, 3, 4, 5, 6 and 7 years after the procedure.

Material and method

We conducted a retrospective study on a group of 114 eyes from 91 patients, diagnosed with different stages of keratoconus and treated from 2006 to 2009 with “epi-off” cross-linking technique at OPTILENS (now OCULENS) Ophthalmology Clinic in Cluj-Napoca, Romania. All the cases were followed-up at 1,3 and 6 months and at 1,2,3,4,5,6 and 7 years.

The inclusion criteria were: patients with age between 15 and 54 years old, both genders, different stages of keratoconus and average corneal thickness of at least 400μm.

The exclusion criteria were: patients with corneal thickness under 400μm, with Vogt striae, herpetic keratitis or other corneal infections, patients with dry eye syndrome and patients with aphakia.

Preoperative, all the patients had a complete ocular examination, consisting of:

uncorrected (UCVA) and best-corrected (BCVA) visual acuity;
refractometry measured by Topcon auto refracto-kerato-meter;
keratometry measured by Topcon refracto-kerato-meter;
slit lamp examination;
intra-ocular pressure;
eye fundus examination;
ultrasonic pachymetry measured by Peschke Pachymeter;
corneal topography and optic pachymetry measured by Tomey TMS-4 Topographer (for 2006 and 2007 cases) and by OCULUS Pentacam Topographer (for 2008 and 2009 cases);
specular microscopy.

The cross-linking procedure was performed in the operating room in sterile conditions. The procedure used was the “epi-off” technique according with the “Siena protocol”.

An informed consent was obtained from all the patients before the procedure.

The steps of the procedure were as follows.

A single 3.0mL of the riboflavin 0.1%–dextran 20% solution was opened and the power of the UVA illuminator was verified. The eye was prepared with topical anaesthesia (alcaine solution), 3–4 drops, 15–20minutes before cross-linking. Sterile operating field and lid speculum was used. A corneal de-epithelization on a 9mm diameter was performed. Instillation of one drop of alcaine solution. Instillation of riboflavin 0.1% every 3minutes for 30minutes before irradiation. The central part of the cornea was exposed at the UV light and instillation of riboflavin was performed every 3minutes for 30minutes, under a power of 3mW/cm2. After irradiation, the cornea was washed with BSS solution. At the end of the procedure, topical antibiotics and steroids were applied and a therapeutic contact lens for 3–4days.

Postoperative treatment consisted of topical steroids and artificial tears for 2 to 3months. The postoperative check-up was made at 24, 48 and 72hours. Follow-up was made at 1, 3 and 6months and 1, 2, 3, 4, 5, 6 and 7years after the procedure.

The statistical analysis was performed with independent “Student t -test”, a method of decision to help us validate or invalidate a statistical hypothesis with a certain degree of safety. The test could be applied because the value samples (refractometry, keratometry, visual acuity) were independent for each case. We consider the normal value statistically significant with P -value<0.05.

Results

The majority of patients were male, 69 eyes (60.52%).

The average age was 26.51years and almost half of the cases, 47.35% (54 eyes) were between the age of 20 and 30 years. Also, despite the literature, we had quite a lot of progressive KCN cases over the age of 30, 24 cases representing 21.05%.

Regarding the grade of keratoconus by Krumeich Amsler classification, 30.7% of cases (35 eyes) were stage II followed by 23.7% (27 eyes) were stage II/III. In a small percentage of cases (7% – 8 eyes), we had keratoconus stage III/IV.

Evolution of flat keratometric values showed an almost unchanged average flat K values at 1month postoperative (0.11 D), a rapid decrease of average flat K values in the first 6months up to 1year, approximately 1 D (1.13 D) comparative with almost stable values between 1 year and 7 years of follow-up (0.56 D), with unsignificant P -value (>0.05) at 1 (0.2303) and 3 (0.0566) months and statistically significant P -value (<0.05) at 6months and 1year (1.92861×10−5) to 7years (2.07975×10−9) (Figure 1A).



Figure 1


Figure 1. 

Evolution of average flat and steep K (from preoperative to 7years follow-up). A. Evolution of flat keratometric values. B. Evolution of steep keratometric values.

Zoom

The difference between preoperative and postoperative average flat K was at 1 year 1.13 D and at 7 years 1.69 D.

Evolution of steep keratometric values was the same as flat keratometry and showed a low decrease of average steep K values at 1month postoperative comparative to preoperative (0.13 D), a rapid decrease of average steep K values in the first from 3months up to 1year (1.10 D) comparative with stable values between 2years and 7years of follow-up (0.54 D), with unsignificant P -value (>0.05) at 1 (0.2473) and 3 (0.0501)months and statistically significant P -value (<0.05) at 6months (0.0501559) and 1year (0.0038247) to 7years (5.04903×10−7) (Figure 1B).

The difference between preoperative and postoperative average flat K at 1year 1.101 D and at 7years 2.05 D.

Evolution of average spherical equivalent evolution showed a decrease of –0.75 D in the first 6months and up to –0.94 at 1year. The average SE decreased at –1.2 D at 2years postoperative and –1.66 at 7years postoperative with a difference of –0.46 D and P- values statistically significant (>0.05) from 3months (0.0006135) to 7years (0.0000829) of follow-up (Figure 2A).



Figure 2


Figure 2. 

Evolution of average spherical equivalent and cylinder values (from preoperative to 7years follow-up). A. Spherical equivalent evolution. B. Cylinder evolution.

Zoom

Like SE, average cylinder decrease was insignificant at 1month postoperative (–0.10 D). Average CYL evolution showed a decrease of –0.60 D in the first 6months and up to –0.80 at 1year. The average CYL decrease stabilized around –0.9 D from 3 to 7years of follow-up with a difference of –0.028 D. P- value was statistically significant (>0.05) from 3months (0.0106284) to 7years (0.0019725) (Figure 2B).

In case of UCVA, lost approximately a line on log Mar scale and presented a slight decrease at 1month postoperative from an average of 0.786 log Mar to 0.87 but gained, at 7years postoperative, a –1.03 log Mar line, to an average UCVA of 0.67 with P -value statistically significant from 1year to 7years of follow-up (Figure 3).



Figure 3


Figure 3. 

Evolution of uncorrected visual acuity.

Zoom

In case of BCVA, preoperative was 0.64 log Mar, presented a slight increase to 0.61 average at 1month postoperative, was 0.528 at 1 after the procedure and stabilized at an average of 0.5 log Mar lines from 2 to 7years of follow-up. P -value was statistically significant (>0.05) from 6months to 7years (Figure 4).



Figure 4


Figure 4. 

Evolution of best-corrected visual acuity.

Zoom

Discussions

Over the past decade corneal collagen cross-linking has been introduced as a treatment in order to stop or hold the progression of KCN. The technique was based on the fact that the decreased biomechanical strength of the cornea, in eyes with KCN may be related to a decrease in intra-inter-fibrillar cross-links within collagen fibers [5].

In our study, we used the standard “epi-off” collagen cross-linking technique in which we exposed the UV-A light radiation, 370μm at 3mW/cm2 and after the removal of the corneal epithelium, riboflavin was instilled each 3minutes for 30minutes, comparing with the “Dresden Protocol” in which the riboflavin was instilled each 5minutes for 30minutes.

The keratometric results in our study showed a decrease in flat K of 1.69 D at 7years and in steep K of 2.05 D at 7years. Comparing with our study, Raiskup-Wolf et al. confirmed earlier findings of statistically significant improvement in K max and astigmatism [6]. The same author, in a 10-year study conducted on 34 cases, showed that the mean values for maximum K (53.2 D and 49.56 D, respectively) and minimum K (47.5 D and 45.5 D, respectively) were significantly lower (P <0.01) [7]. Witting-Silva et al. reported in their study significant flattening of steepest simulated keratometry values, of 1.45 D after 1 year postoperative [8]. Coskunseven et al. showed, in their study, that the maximal curvature decreased by 1.57±1.14 D [9]. Hersh et al. demonstrated a significant decrease in K max (2.0±4.4 D) and average keratometry (1.5 D) at 1 year after cross-linking [10]. Sedaghat et al. presented a 1-year follow-up study based on 97 cases, where average keratometry value decreased from 49.62 to 47.95, which is conclusive with our results at 1-year follow-up [11]. The first in vitro study, of Wollensak et al. showed that the CXL technique was efficient in halting the progression of KCN over a period of up to 4 years. They revealed a reduction of K max by 2.01 D. Khattak et al., in a study on 51 cases, at 1 year after the procedure, presented that there was significant flattening of the average keratometry by 0.61 D, which is conclusive with our study where at 1year follow-up, flat K decreased with 1.13 D and steep K with 1.10 D [12, 13].

Our results regarding spherical equivalent and cylinder values showed a decrease of 0.8 D at 1year and 0.9 at 7years of follow-up, respectively 0.94 D at 1year and 1.66 D at 7years follow-up, which was statistically significant (P <0.05). Coskunseven et al. demonstrated a mean decrease in spherical equivalent refraction and cylinder, statistically significant [9]. Sedaghat et al., in their study, revealed that cylinder values decreased by 0.6 D, from 4.84 to 4.24 [11]. Pahuja et al. showed that cylinder (P =0.0003) and spherical equivalent (P =0.02) reduced significantly after CXL [14]. Sharma et al. presented a study on 43 eyes, with moderate to severe KCN, with results conclusive with our study. They showed that refractive cylinder and spherical equivalent decreased by mean of 0.62 D (P =0.01) and 0.5 D (P =0.019), respectively [15].

The UCVA gained at 7years postoperative, a –1.03 log Mar line, to an average of 0.67, with P -value statistically significant from 1year to 7years of follow-up. BCVA was 0.528 at 1year after the procedure and stabilized at an average of 0.50 log Mar lines from 2 to 7years of follow-up, gaining an average of 1.51 log Mar lines. Our results are according to those showed by Vinciguerra et al. in his prospective, non-randomized single center clinical trial [16]. Increasing of UCVA and BCVA was also published by Hersh et al. [10]. Coskunseven et al. demonstrated an increasing UC and BCVA after cross-linking, comparative to controls (P <0.01) [9]. Sedaghat et al. presented in his study that UCVA improved from 0.31 to 0.45 and BCVA improved from 0.78 to 0.84 [11]. Sadoughy et al. demonstrated in their study that there was significant increase in UCVA (0.54±0.35 log Mar preoperatively to 0.49±0.34 log Mar postoperatively, P =0.01) and BCVA (0.21±0.19 log Mar preoperatively, to 0.16±0.17 log Mar postoperatively, P =0.01), results which were conclusive with the ones demonstrated in our study [17].

Recent data suggests that patients with advanced KCN can be stabilized by CXL procedure [18]. In children and teenagers, with accelerated progression of KCN, it was proven that CXL has to be done earlier than later [19, 20].

In our opinion, the decrease of K values can be explained that almost half of the cases are between 20 and 30 years old and the cornea is more elastic in these patients. Another explanation is the application of the “epi-off” technique in which the riboflavin penetrates the cornea deeper.

We already know that in keratoconic corneas there are signs of oxidative damage with low levels of antioxidation and lipid peroxidation enzymes for elimination of toxic elements [21]. Also, it is known that KCN corneas have increased levels of numerous enzymes capable of degrading a wide variety of corneal extracellular matrices. All these enzymes are associated with oxidative stress [22]. Performing CXL on keratoconic corneas maybe we can interfere with the oxidative stress and “find the common pathway” for KCN.

Conclusions

Cross-linking is a real breakthrough in the treatment of keratoconus and corneal ectasia. This procedure slows or stops the progression of keratoconus in order to avoid or delay the necessity of corneal transplantation.

Corneal stabilization can be achieved by CXL procedure and the results at 7years are stable, consisting of reduction of keratometric values, cylinder and spherical equivalent and increased visual acuity.

In our study, the stopping of KCN progression and stability of cross-linking is demonstrated by the fact that after 7years, none of the patients had to suffer corneal transplantation.

The article presents a rare case of a long-term study on the progression of KCN after CXL treatment.

Role of financial source

There is no financial interest or disclosure from none of the authors.

Disclosure of interest

The authors declare that they have no competing interest.


 The manuscript was presented by Assoc. Prof. Dr. Cristina Nicula, on Friday 30th of September, as a paper presentation, at the 46th ECLSO Congress in Paris, 30th September–1st October 2016.

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