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   Table of Contents      
ORIGINAL ARTICLE
Year : 2017  |  Volume : 4  |  Issue : 2  |  Page : 62-65

Basic assessment of corneal collagen cross-linking in Sudanese sample


1 Department of Optometry, Makkah Eye Hospital, Khartoum, Sudan
2 Department of Optometry, Al-Neelain University, Khartoum, Sudan

Date of Web Publication21-Sep-2017

Correspondence Address:
Atif Babiker Mohamed Ali
Department of Optometry, Al-Neelain University, Khartoum
Sudan
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DOI: 10.4103/bijo.bijo_3_17

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  Abstract 


Background: Collagen Corneal Cross-Linking (CXL) is a surgical technique that combines ultraviolet light and riboflavin eye drops as a one of the modern therapies for keratoconus.
Objectives: This retrospective study aimed to assess the visual outcome, corneal curvature, corneal thickness, and refractive status after CXL.
Methods: The records of 25 patients did CXL during May 2012 to May 2014 at Makkah Eye Hospital were reviewed. The recorded data included uncorrected and best-corrected visual acuity (Nidek Chart Projector CP 670 Japan), central corneal thickness and average K-readings (ATLAS 9000, Corneal Topography System, Germany), and refraction (Nidek Auto Refractometer, AR310A Japan); all these measurements were taken at baseline before CXL and after 1 year post-CXL.
Results: The age range of this group was 12–26 years of whom 60% females and 40% males. A little improvement of vision was achieved from a presenting mean 6/30 to CXL mean 6/20 at P = 0.024. No significant difference was observed in corneal central thickness preoperative mean 447.72 ± 27.52 μm) and postoperative (mean 448.83 ± 22.35 μm). K-readings showed only limited changes in the form of astigmatism and not in the degree of astigmatic error (mean 2.80 ± 1.327 D) preoperative and (mean 3.08 ± 1.717 D) postoperative. A moderate spherical refractive error (noncorneal) was persisting (mean 2.79 ± 2.09 D preoperative and 2.66 ± 2.10 D postoperative).
Conclusions: CXL assumes controlling of corneal ectasia and regarded as one of effective procedures in improving the vision, particularly when combined with optical correction.

Keywords: Corneal central thickness, collagen corneal cross-linking, keratoconus, K-reading and refraction, vision


How to cite this article:
Abdellah AK, Mohamed Ali AB. Basic assessment of corneal collagen cross-linking in Sudanese sample. Albasar Int J Ophthalmol 2017;4:62-5

How to cite this URL:
Abdellah AK, Mohamed Ali AB. Basic assessment of corneal collagen cross-linking in Sudanese sample. Albasar Int J Ophthalmol [serial online] 2017 [cited 2017 Dec 11];4:62-5. Available from: http://www.bijojournal.org/text.asp?2017/4/2/62/215282




  Introduction Top


The adult average cornea is 500 μm thick; however, in some cases, the cornea becomes thinner which leads to visual distortions and keratoconus.[1] This degenerative noninflammatory disorder of the eye often onsets during the teenage years or early twenties with decreased vision, and light sensitivity also may be noticed.[2] Keratoconus can be difficult to detect in the early stage because it usually develops slowly; however, in some cases, it may proceed rapidly; as the cornea becomes more irregular in shape, it causes progressive myopia and irregular astigmatism.[3] Keratoconus shows an autosomal dominant mode of inheritance, a positive family history; it has been found in all races and in both sexes but found to affect females more often than males.[4]

Keratoconus affects between 50 and 230/100,000. A racial factor as well as climatic conditions may play a role. A relatively high incidence has been documented in the Mediterranean and a Middle Eastern area; a relatively lower incidence has been reported in places such as Japan, Taiwan, and Singapore. Males may be at higher risk than females; in addition, the prevalence of the condition is about 7% in Down's syndrome.[5]

A number of optical, medical, and surgical approaches have been used in the treatment of keratoconus including spectacles which help in mild or moderate keratoconus.[4] Contact lenses are useful in moderate and advanced keratoconus soft or hard contact lenses can be tried to provide adequate vision correction.[4] Surgical intervention could be alternative choices if eyeglasses or contact lenses cannot control keratoconus. Surgical therapies include three ways according to stage and form of keratoconus: keratoplasty used if the keratoconic patient does not tolerate hard contact lenses; full thickness corneal transplant may be the last remedy to be considered. Intacs are corneal implant devices minimally invasive used for the treatment of keratoconus. Collagen corneal cross-linking (CXL), a medical process of using ultraviolet (UV) light and riboflavin eye drops, was introduced in the late 1990s. By actively increasing the degree of covalent bonding between and within the molecules of extracellular matrix, such as collagen Type I and proteoglycans, therapeutic cross-linking was reasonably expected to enhance corneal rigidity and to slow or even arrest the progression of keratoconus.[6] The CXL can be done by many protocols and procedures depending on the individual compliance and cooperation.[7] A standard CXL procedure begins with removal of central 7–9 mm of corneal epithelium under local anesthesia, and riboflavin (Vitamin B2) is dripped into the cornea until they penetrate the entire cornea. Evidence of penetration into the anterior chamber of the eye is demonstrated by slit-lamp evaluation (riboflavin 0.1% suspended in a dextran T500 20% solution). The patient's eye is exposed to ultraviolet Type A (UVA radiation of 370 nm wavelength and an irradiance of 3 m W/cm 2 at a distance of 5.4 mm from the cornea, applied for 30 min, delivering a dose of 5.4 J/cm 2). This process leads to the formation of bonds between collagen molecules allowing it to reform new cross-links between the collagen. Antibiotic eye drops are instilled as prophylaxis. A bandage contact lens is inserted which is then removed at the follow-up visit once epithelial healing is complete. Follow-up on a regular basis for several months, many patients notice an improvement in their vision at 3–6 months.[8],[9],[10],[11]


  Methods Top


This retrospective study involved 25 keratoconic patient's data collected from cornea clinic in Makkah Eye Hospital during May 2012 to May 2014. The data included age, gender, visual acuity for distance with and without correction (Nidek Auto Chart Projector Model CP 670 Japan), auto-refraction (Nidek Auto Refractometer, AR310A Japan), and central corneal thickness and K-reading ( Atlas More Details 9000, Corneal Topography System, Germany); the process of analysis is dependent on the patient's present examination data before the CXL operation compared to the data after 1 year post-CXL operation to evaluated the outcome.


  Results Top


In [Table 1],[Table 2],[Table 3]: The age range of this group was 12–26 years of whom 60% females and 40% males. A little improvement of vision was achieved from a presenting mean 6/30 to CXL mean 6/20 at P = 0.024. No significant difference was observed in corneal central thickness preoperative mean 447.72 ± 27.52 μm) and postoperative (mean 448.83 ± 22.35 μm). K-readings showed only limited changes in the form of astigmatism and not in the degree of astigmatic error (mean 2.80 ± 1.327 D) preoperative and (mean 3.08 ± 1.717 D) postoperative. A moderate spherical refractive error (noncorneal) was persisting (mean 2.79 ± 2.09 D preoperative and 2.66 ± 2.10 D postoperative).
Table 1: The descriptive statistics of patient's data

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Table 2: Paired correlations pre- and post-collagen corneal cross-linking

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Table 3: t-test of patient's data

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  Discussion Top


This study shows a preliminary assessment of collagen CXL as treatment of keratoconus in a Sudanese sample. The sample size in this study was 25 subjects which is relatively small. However, this is due to the small number of patients who did the operation during 2 years of time. Although a relatively high incidence has been documented in the Mediterranean and Middle Eastern areas.[5] Therefore, the results should be interpreted with caution and this sample was likely to be accepted as representative for the initial assessment in our community. The age range of the sample was 12–26 years, with a mean 17.20 ± 4.17 standard deviation; this is the age of adolescence, and major changes and development in eye structure were expected during this period. There were more females (60%) than males (40%) among the group. According to the study of Koppen,[5] males may be at higher risk of keratoconus than females. However, when looking at personality traits, the keratoconic females have shown increased rates of depression. However, the more female's preponderance in this group is unlikely to cause an effect in results of this study. Visual acuity is the conventional and standard test most commonly used test to assess visual function. The Snellen-based charts are universally accepted tools for testing visual acuity despite its poor reliability and reproducibility.[12] Visual acuity in this study is the only tool used to evaluate the effect of CXL on presenting vision. In spite of apparent little improvement between mean of presenting vision (6/30) and CXL vision (6/20) [Table 1] but t-test showed (t = −2.408; P = 0.024) [Table 3], this is a significant improvement in vision. However, this may be of more practical importance as compared to best spectacle-corrected visual acuity in which the mean achieved was 6/18 [Table 1]. Since the spectacle correction needs a high degree of cylinders which will have some drawbacks with binocularity when using same optical lens for distance and near-vision as well as the cylinder distortion and difficulties in manufacturing of such lenses; collagen CXL can be a good alternative treatment of keratoconus instead of lenses.

The majority of studies revealed the keratoconic patients have corneal central thickness (CCT) less than the normal-mean (500 μm). In this study report, no significant difference was observed among the group in terms of CCT preoperative (mean 447.72 ± 27.52 μm) and postoperative (mean 448.83 ± 22.35 μm) [Table 1]. That is the CCT seems to show a mild change in some cases after the process of CXL and this was clearly proved by the strong correlation (r = 0.821 and P ≤ 0.0001). On the other hand, corneal thinning could be maximum corresponds to the site of maximum steepening, and a computerized corneal topography analysis may be essential. However, therapeutic cross-linking was reasonably expected to enhance corneal rigidity and to slow or even arrest the progression of keratoconus but not affecting the CCT according to Taneri et al.[11],[12]

Spectacle correction of refractive error in keratoconic patients would not reduce the burden of visual impairment in this population due to the corneal surface defects which frequently progress and reduce acuity. Thus, even minor structural changes can alter the optical quality. Therefore, the challenge is to select the most suitable type of correction which will provide most comfortable vision. In this study, K-reading shows high degrees of astigmatic errors without significant changes (mean 2.80 ± 1.327 D) preoperative and (mean 3.08 ± 1.717 D) postoperative [Table 1] as well as a weak correlation [Table 2] and [Table 3]. However, in most of the cases, there is irregular astigmatism where the principal meridians are no longer 90° apart and the mires cannot be superimposed clearly. Therefore, after CXL, there is a change in the form of astigmatism and not in the degree. This change was clearly approved by significant K-readings pre- and post-CXL (t = 4.987, P < 0.0001). The findings of this report indicate that the contribution of spherical refractive error (noncorneal) is also moderate (mean 2.79 ± 2.09 D preoperative and 2.66 ± 2.10 D postoperative). Therefore, the present results assume that the uncorrected residual refractive error was an additional source which reduced the visual capability in this group.


  Conclusions Top


This study has shown that collagen cross-linking appears to be effective in stopping the progression of keratoconus. Although no significant structural changes were noticed statistically from the results, follow-up to 12 months revealed that there was slow and continuous improvement of vision. This improvement could be satisfactory to most of the patients if combined with optical correction of spectacles or contact lenses.

Future studies

More longitudinal and prospective studies of sufficient sample size including procedures for measuring stability and rigidity of the cornea after CXL are highly required. Higher-order aberrations are also significantly correlated with corneal operations. However, examinations and assessments including prominent aberrations are essentials in eyes with CXL.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Kunimoto D, Kanitkar K, Makar M. The Wills Eye Manual. Philadelphia: Lippincott Williams & Wilkins; 2004.  Back to cited text no. 1
    
2.
Lang G. Ophthalmology a Pocket Textbook Atlas. 2nd ed. Stuttgart New York: Thieme; 2006.  Back to cited text no. 2
    
3.
Stabuc-Silih M, Strazisar M, Ravnik-Glavac M, Hawlina M, Glavac D. Genetics and clinical characteristics of keratoconus. Acta Dermatovenerol Alp Pannonica Adriat 2010;19:3-10.  Back to cited text no. 3
    
4.
Mirza UB, Iqbal Y, Haq MI. Visual and keratometric results after corneal collagen cross linking in keratoconus. Pak J Ophthalmol 2012;28:P.115-120.  Back to cited text no. 4
    
5.
Koppen C. Corneal cross-linking and keratoconus: The change in treatment paradigm of keratoconus. Bull Soc Belge Ophthalmol 2012;321:5, 9-23, 25-7.  Back to cited text no. 5
    
6.
Wollensak G. Crosslinking treatment of progressive keratoconus: New hope. Curr Opin Ophthalmol 2006;17:356-60.  Back to cited text no. 6
    
7.
Kanellopoulos AJ. PRK: Present, Past, and Future. Slack Incorporated; 2012. 6900 Grove Road, Thorofare, NJ; United States 8086, Available from: www.slackbooks.com. [Last accessed on: 2017 Sep 10].  Back to cited text no. 7
    
8.
Caporossi A, Mazzotta C, Baiocchi S, Caporossi T, Denaro R. Age-related long-term functional results after riboflavin UV a corneal cross-linking. J Ophthalmol 2011;2011:608041.  Back to cited text no. 8
    
9.
Friedman MD, Pertaub R, Usher D, Sherr E, Kamaev P, Muller D. Advanced corneal cross-linking system with fluorescence dosimetry. J Ophthalmol 2012;2012:303459.  Back to cited text no. 9
    
10.
Chang CY, Hersh PS. Corneal collagen cross-linking: A review of 1-year outcomes. Eye Contact Lens 2014;40:345-52.  Back to cited text no. 10
    
11.
Taneri S, Jarade E, Kanellopoulos JA, Muller D. Current concepts and future developments of corneal cross-linking. J Ophthalmol 2015;2015:302983.  Back to cited text no. 11
    
12.
Hussain B, Saleh GM, Sivaprasad S, Hammond CJ. Changing from Snellen to LogMAR: Debate or delay? Clin Exp Ophthalmol 2006;34:6-8.  Back to cited text no. 12
    



 
 
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  [Table 1], [Table 2], [Table 3]



 

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