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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 21  |  Issue : 3  |  Page : 153-158

Corneal endothelial changes evaluation using specular microscope following collagen cross-linking in treatment of keratoconus


1 Department of Ophthalmology, Faculty of Medicine, Damietta, Egypt
2 Department of Ophthalmology, Faculty of Medicine for Girls, Al-Azhar University, Cairo, Egypt

Date of Submission24-Mar-2020
Date of Decision08-May-2020
Date of Acceptance27-May-2020
Date of Web Publication23-Sep-2020

Correspondence Address:
MBBCh Reem S Eid
Ezbat El-Lahm in front of Damietta Police Station, Damietta 34734
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/DJO.DJO_27_20

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  Abstract 


Objective The aim of this study was to evaluate the corneal endothelial changes following corneal collagen cross-linking treatment of keratoconus using a specular microscope.
Patients and methods The study included 30 eyes of 30 patients with keratoconus, comprsing 16 males and 14 females, with a mean age of 28 years. Patients had a standard corneal collagen cross-linking after removal of the corneal epithelium. They were evaluated before and 1 month after the procedure using the specular microscope.
Results The mean preoperative central corneal thickness of the patients was 477.5±35.57 µm, and at 1 month postoperatively, it was 477.9±36.88 µm, with no statistically significant change (P=0.7821). The mean preoperative value of cell density was 2963.1±364.1 cells/mm2 and became 2956.96±363 cells/mm2 1 month postoperatively, with no statistically significant change (P=0.7091). The mean preoperative coefficient of variation value was 36.3±5.9%, whereas 1 month postoperatively, it became 36.2±5.6%, with no statistically significant change (P=0.6951). The mean preoperative value of hexagonal cells was 49.93±7.9% and became 48.5±7.3% 1 month postoperatively, with no statistically significant change (P=0.2078).
Conclusion There were no significant changes in human corneal endothelial parameters, as evaluated with the specular microscope, following cross-linking in keratoconic eyes.

Keywords: corneal endothelium, cross-linking, keratoconus, specular microscope


How to cite this article:
Elgazzar AF, Eid RS, Aly MM. Corneal endothelial changes evaluation using specular microscope following collagen cross-linking in treatment of keratoconus. Delta J Ophthalmol 2020;21:153-8

How to cite this URL:
Elgazzar AF, Eid RS, Aly MM. Corneal endothelial changes evaluation using specular microscope following collagen cross-linking in treatment of keratoconus. Delta J Ophthalmol [serial online] 2020 [cited 2020 Oct 20];21:153-8. Available from: http://www.djo.eg.net/text.asp?2020/21/3/153/295881




  Introduction Top


Keratoconus is an asymmetrical and progressive corneal ectasia that leads to visual impairment by causing irregular astigmatism, myopia, higher order aberrations, and corneal scaring [1]. It develops in the puberty period and affects both sexes. Although its pathogenesis has not been clarified yet, it has been shown that environmental and genetic factors play a role in the onset of the disease. It is characterized by changes in the structure of the corneal epithelium and stromal thinning [2]. Despite the fact that only one eye may be affected initially, keratoconus ultimately affects both eyes [3].

The clinical diagnosis of moderate and severe keratoconus is not a major challenge and can be detected using retinoscopic and keratometric findings. However, the diagnosis of subclinical keratoconus can be difficult. Pentacam examines the anterior and posterior corneal surfaces, and studies have shown that its measurements are highly accurate and repeatable [4].

Spectacles, rigid gas-permeable contact lenses, and insertion of corneal ring segments are the treatment modalities commonly applied to improve the visual function. However, these treatment modalities do not stop the progression of the disease [5]. Corneal collagen cross-linking (CXL) is used to prevent progression in early and middle stages of the disease. In the late stages, penetrating keratoplasty and deep anterior lamellar keratoplasty can be performed to increase the patient’s visual acuity [6].

The current goal is to stop disease progression, rather than trying to heal the disease. Cross-linking leads to a higher degree of stiffness of the cornea and inhibits further progression [7]. In this procedure, the application of riboflavin (a photosensitizer) and ultraviolet-A (UVA) light induces covalent bonds, known as cross-links, between the collagen fibrils. These cross-links are believed to improve the overall strength of the tissues, halt outward bulging, and eventually help patients restore visual acuity [8].

The commonly used cross-linking protocol is the epithelial off (epi-off) CXL. The ‘Dresden protocol’ (standard protocol) includes removal of the central 8–9 mm of the corneal epithelium, application of 0.1% riboflavin solution every 5 min for 30 min, followed by exposure to UVA (370 nm, 3 mw/cm2) for 30 min. Other protocols include epithelial on (epi-on) CXL and accelerated CXL [9].

The aim of this study was to evaluate the corneal endothelial changes using a specular microscope after 1 month of CXL procedure in the treatment of keratoconus.


  Patients and methods Top


This is a prospective, nonrandomized, interventional case series study that included 30 eyes of 30 patients with keratoconus, comprising 16 males and 14 females, with a mean age of 28±6.2 years. All patients were evaluated by the specular microscope (Topcon SP-1P; Topcon Medical Inc., Tokyo, Japan) at Damietta Ophthalmology Hospital, Damietta, Egypt, before and 1 month after being subjected to standard collagen cross-linking. All patients signed a written informed consent to participate in the study and for publication of data. The study was approved by the Local Ethics Committee of Al-Azhar University.

Both sexes were included with age range from 18 to 45 years. Patients had keratoconus with central corneal thickness (CCT) more than 400 µm as measured with the Pentacam (HR; Oculus Optikgeräte GmbH, Wetzlar, Germany).

Patients with pachymetry thinner than 400 µm, prior herpetic ocular infection, severe corneal scarring, prior intraocular surgery, autoimmune disorders, and pregnancy were excluded from the study.

All participants were subjected to:
  1. Demographic data: age, sex, history of intraocular surgery, neurologic, metabolic, or systemic diseases.
  2. Full ophthalmological examination, including visual acuity assessment (uncorrected visual acuity and best-corrected visual acuity) using the Landolt’s broken ring chart, refraction measurement using an autorefractometer (Topcon Medical System, Oakland, New Jersey, USA), anterior segment slit lamp examination, and fundus examination using a Volk lens +90 diopters (D).
  3. Measurement of CCT using Pentacam (HR; Oculus Optikgeräte GmbH).
  4. Evaluation of corneal endothelium with a noncontact specular microscope (Topcon SP-1P; Topcon Medical Inc.).
  5. Application of standard CXL for prevention of progression of keratoconus.
  6. Re-evaluation of corneal endothelium after 1 month of cross-linking with the specular microscope.


Surgical procedure

All patients were treated with UVA/riboflavin CXL under sterile conditions in the operating room. The periocular skin was scrubbed with 10% povidone-iodine (Betadine 10%; El-NILE Co., Cairo, Egypt). The central corneal area was exposed by an eye speculum. Topical anesthesia was done by using benoxinate hydrochloride 0.4% eyedrops (Benox 4%; Epico Inc., Cairo, Egypt), used twice once before starting the procedure and once before UVA exposure. A microsponge soaked with ethyl alcohol 20% was applied to the central part of the cornea for 15 s. Then, an 8.0-mm diameter of the central corneal epithelium was removed using forceps. This was followed by application of 0.1% isotonic riboflavin and hydroxylpropyl methylcellulose (HPMC, VibeX Rapid; Avedro Inc., Waltham, Massachusetts, USA) that was instilled every 5 min for 30 min. Then UVA irradiation was applied for 30 min at an 8-mm treatment zone using a UVA system device (OPTO XLink-corneal cross-linking system; Opto Global Pty Ltd). The parameters of the device were set to time (T) of 30 min, and the other parameters were automatically set including the irradiance range (I) and power of UVA. At the end of the procedure, a soft bandage contact lens was applied. Medical treatment was administrated, and all patients were followed up until re-epithelialization occurred.

Statistical analysis

Data entry, processing, and statistical analyses were carried out using MedCalc version 18.2.1 (MedCalc, Ostend, Belgium). Tests of significance used included Student’s t test, Paired t test, χ2 test, factorial and repeated measures analysis of variance, and Pearson’s correlation analysis. Data were presented, and suitable analysis was done according to the type of data (parametric and nonparametric) obtained for each variable. Mean, SD, and range were used for parametric numerical data, whereas median and interquartile range were used for nonparametric numerical data. Frequency and percentage were used for nonnumerical data. P values less than 0.05 (5%) were considered to be statistically significant.


  Results Top


The study included 30 eyes of 30 patients with keratoconus, comprising 16 (53.3%) males and 14 (46.7%) females. The mean age of the patients was 28±6.2 years. All patients completed 1 month of follow-up after treatment.

The mean preoperative CCT was 477.5±35.57 µm, whereas the mean value at 1 month postoperatively was 477.9±36.88 µm, with no statistically significant difference between the two values (P=0.7821, [Figure 1]).
Figure 1 Comparison between preoperative and 1-month postoperative central corneal thickness (CCT) measurements in eyes with keratoconus.

Click here to view


The mean preoperative value of endothelial cell density (CD) was 2963.1±364.1 cells/mm2, whereas the mean value at 1 month postoperatively was 2956.96±363 cells/mm2, with a statistically nonsignificant difference (P=0.7091, [Figure 2]).
Figure 2 Comparison between preoperative and 1-month postoperative cell density (CD) measurements in eyes with keratoconus.

Click here to view


The mean preoperative coefficient of variation (CV%) was 36.3±5.9%, whereas 1 month postoperatively, it was 36.2±5.6%, with a statistically insignificant difference (P=0.6951, [Figure 3]).
Figure 3 Comparison between preoperative and 1-month postoperative coefficient of variation (CV) measurements in eyes with keratoconus.

Click here to view


The mean preoperative value of hexagonal cell % (Hex. %) was 49.93±7.9%, whereas the mean 1-month postoperative value was 48.5±7.3%, with no statistically significant difference (P=0.2078, [Figure 4]).
Figure 4 Comparison between preoperative and 1-month postoperative hexagonal cell % (Hex.) measurements in eyes with keratoconus.

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  Discussion Top


The current study showed that there were no statistically significant changes in all corneal endothelial parameters evaluated with the specular microscope (including CCT, CD, CV%, and Hex. %) after 1 month of a standard cross-linking procedure in keratoconic patients.

Similar to the present study, Razmjoo et al. [10] compared the findings of endothelial specular microscopy in 68 keratoconic eyes before and 1 year after CXL. They found that the CCT had no significant change (470±40 µm, preoperatively and 469.8±42 µm, postoperatively, with P=0.591). In addition, the preoperative percentage of Hex., representing pleomorphism, was 54.14±6%, whereas the postoperative percentage was 54.55% (P=0.517), indicating no significant change in cell shape. Contrary to the present study, they showed that there was a significant reduction in CD, but this reduction was low (∼60 cells; 2753±230 cells/mm2, preoperatively, and 2699±210 cells/mm2, postoperatively, with P=0.004). In addition, the cell size (polymegathism) represented by the CV% was significantly increased (32.72±10.14%, preoperatively, and 40.21±9.7%, postoperatively, with P=0.021).

Similarly, Arora et al. [11] worked on 30 eyes that were divided into two groups according to the mean central keratometry (A<53 D, B>53 D) and followed them up for 1 year. They reported no statistically significant difference in the CD in both groups after the cross-linking procedure. Contrary to the current study, they reported that there was a statistically significant decrease in the CCT at all follow-up visits in both groups (P=0.001).

Rechichi et al. [12] did CXL to 28 eyes and followed them up for 1 year. They showed that there was a statistically insignificant difference in CD (2501±26 cells/mm2, preoperatively; and 2502±30 cells/mm2, after 1 month; and 2487±26 cells/mm2, after 1 year). However, they showed that there was a significant decrease in CCT after the cross-linking procedure (444±28 μm, preoperatively and 432.88±28 μm, postoperatively).

Magli et al. [13] did epi-off cross-linking in 23 pediatric keratoconic eyes and followed them up for 1 year. There was no significant change in CD (3212±331.1 cells/mm2, preoperatively and 3188±147.1 cells/mm2, after 12 months, with P=0.7). In addition, there was no significant change in the CCT following CXL (487.2±15.1 µm, preoperatively and 492±22.1 µm, after 12 months, with P=0.5).

Similarly, Kymionis et al. [14], during a 1-year follow-up of 38 CXL treated eyes, found an unaltered endothelial cell layer, with no significant change in CD after the cross-linking procedure (2756±78 cells/mm2, preoperatively, and 2698±87 cells/mm2, 1 year postoperatively).

Asri et al. [15] worked on 54 eyes and followed them up after 1, 3, 6, and 12 months, postoperatively. There was no significant change in CD after the cross-linking procedure at all follow-up visits (P=0.07 at 12 months). However, there was a significant decrease in CCT from 442±49 μm preoperatively to 409±67 μm at 12 months postoperatively.

Caporossi et al. [16] evaluated 44 eyes with keratoconus with a minimum follow-up period of 48 months before and after epi-off CXL. There was no significant change in CD. In addition, the CCT showed a statistically nonsignificant corneal thinning in the first two postoperative months (450±14.54 µm, preoperatively and 438.177±15.118 µm at the first postoperative month).

Goldich et al. [17] in their study on 14 eyes that were followed up for 1 year found no significant changes in CD after the cross-linking procedure (2730 cells/mm2, preoperatively, and 2640 cells/mm2, at 12 months postoperatively; P=0.21). In addition, the CCT showed no significant changes postoperatively (461±38 µm preoperatively and 478±52 µm at 12 months postoperatively, with P=0.84).

Helal et al. [18] compared the findings of endothelial specular microscopy of 40 keratoconic eyes before and 1 month after standard CXL. There was no significant difference between the preoperative and postoperative values of CD in the cross-linked eyes (2639.68±218.56 cells/mm2 preoperatively and 2617.15±180.34 cells/mm2 at 1 month postoperatively, with P=0.497). In addition, the CCT showed no significant change (466.15±42.98 µm preoperatively and 457.38±46.17 µm at 1 month postoperatively; P=0.190). Similarly, the mean CV% showed no significant difference (29.43±5.35% preoperatively and 30.03±6.01% at 1 month postoperatively, with P=0.385). The Hex. % in the cross-linked eyes showed no significant changes (65.95±8.07% preoperatively and 67.23±9.11% at 1 month postoperatively, with P=0.475).

El-Sayed et al. [19] compared the findings of endothelial specular microscopy of 30 keratoconic eyes before and 6 months after standard CXL. They showed that there was no significant difference between the preoperative and postoperative CD (the mean preoperative and postoperative values of CD were 3221.40±243.16 and 3200.42±247 cells/mm2, respectively). In addition, the CCT showed no significant change (the mean preoperative and postoperative values were 478.38±42.9 and 493.2±16.70 µm, respectively). Contrary to the current study, they found a significant increase in the CV% (the mean preoperative and postoperative CV were 38±3.70 and 41.71±2.74%, respectively). They also found a significant decrease in Hex. % (mean preoperative and postoperative Hex. % were 41.73±5.08 and 38.13±5.24%, respectively).

Tag El-Din et al. [20] performed standard CXL for 15 eyes and followed them up after 1, 3, and 6 months. There were no significant changes in the endothelial cell count (CD was 2476±220 cells/mm2 preoperatively, 2455±210 cells/mm2 after 1 month, and 2434±200 cells/mm2 after 6 months, with P=0.281). The CCT was almost back to its original preoperative value after 3 months (467.17±31.68 µm preoperatively and 459.78±39.63 µm after 3 months, postoperatively).

Vinciguerra et al. [21] carried out a study on 28 eyes and followed them up for 1 year. There was no significant change in CD (P=0.13). Contrary to the present study, there was a significant decrease in the mean baseline pupil center pachymetry with Pentacam from 490.68±30.69 μm preoperatively to 470.09±20.01 μm, postoperatively.

Wollensak et al. [22] in their study on 23 keratoconic eyes, which were followed for 3 months to 4 years, showed that the CD remained unchanged postoperatively (P=0.45).

The limitation of the current study is the short follow-up duration that did not allow for a definitive conclusion regarding the long-term effect of CXL on keratoconic corneal endothelial specular microscopy parameters. So, further studies with longer follow-up period should be performed. Studies with comparison with a control group are also recommended for more valuable results.


  Conclusion Top


CXL in keratoconic patients appears to be safe on human corneal endothelium. There were no significant changes in human corneal endothelial parameters, as evaluated by the specular microscope 1 month after the cross-linking procedure in keratoconic eyes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Rafati S, Hashemi H, Nabovati P, Doostdar A, Yekta A, Aghamirsalim M et al. Demographic profile, clinical, and topographic characteristics of keratoconus patients attending at a tertiary eye center. J Curr Ophthalmol 2019; 31:268–274.  Back to cited text no. 1
    
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El-Saadany A, Ibrahim A, Esaa S. Evaluation of intrastromal corneal rings (two segments vs. keraring 355) in central keratoconus using femtosecond laser. Egypt J Cataract Refract Surg 2018; 24:18–22.  Back to cited text no. 3
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