A retrospective cohort study conducted at Beirut Eye and ENT Specialist Hospital (Lebanon) between January 2010 and June 2015
Patients who underwent CXL surgery for progressive keratoconus and ectasia were followed for 3 years. Review board approved the study which complies with the Declaration of Helsinki.
Study population
Charts of all the patients receiving CXL between January 2010 and June 2015 were reviewed, 158 patients with keratoconus and 62 patients with ectasia were identified.
Inclusion criteria: - Progressive keratectasia (keratoconus or ectasia) based on refraction and topography changes in two consecutive visits (criteria discussed in the following section)
- Patients who presented for follow up at 6 months, 1 year and 3 years
- Minimal central corneal thickness of 330 μm17
- All age groups
Exclusion criteria: - loss of follow up
- Ocular surface pathologies
- Pregnancy during the 3 years of follow up
- Eyes implanted with implantable Collamer lens (ICL) during the follow up period
165 eyes of 98 patients met the inclusion criteria. 54 eyes (31 patients) had ectasia and 111 eyes (67 patients) had keratoconus. Since keratoconus is more prevalent than ectasia a higher number of patients was included. In both keratoconus and ectasia groups, some patients were subject to combined procedures, ICRS or PRK. In order to avoid biased statistics, statistical analysis was first carried in all patients comparing both groups and then patients who had ICRS or/and PRK were excluded from the final analysis comparing ectasia and CXL at different follow up period.(Figure 1)
Keratoconus andEctasia progression
Progression in patients diagnosed with keratoconus and ectasia is suspected if there is deterioration in the visual acuity or the manifest refraction, after an increase in maximum keratometry readings or a decrease in corneal thickness13,18-20. Until now there is no clear definition of progression. The global consensus on Keratoconus and Ectatic Diseases (2015) defined progression by a change in at least two of the following parameters: progressive steepening of the anterior corneal surface, steepening of the posterior corneal surface, and/or thinning or changes in the pachymetric rate of change.18
In our study the progression before and after CXL was diagnosed based on the presence of two or more of the following criteria on two consecutive visits:
- Increase in K values (K1, K2, K max and K mean) >1D
- A change in the map difference between two consecutive readings >1D
- ≥ 2 % decrease in central thickness
- A deterioration of CDVA or uncorrected visual acuity defined as a drop of one or more lines on Snellen chart and that is not attributed to other ocular disorders
- Any significant changes in the magnitude of spherical equivalence, myopic or astigmatic refraction (>1.0D) that is not attributed to any other optical system disorders.
Surgical Procedure
CXL-epithelium off was used for all the surgeries. Proparacaine hydrochloride 0.5% drops were used to anesthetize the eye. After the insertion of a lid speculum, a bunt spatula was used to remove the central 9 mm corneal epithelium. The riboflavin 0.1% dextran solution (Collagex, isotonic 0.1%, Lightmed USA Inc.) was instilled every 2 minutes for 30 minutes. The ultraviolet A (UVA) lamp (UV-X illumination system, version 1000; IROC AG, Zurich, Switzerland) was then focused on the cornea with a radiant energy of 3.0 ± 0.3 mW/cm2 for 30 minutes following Dresden protocol.2 During UVA administration, riboflavin drops were applied to the cornea every 2 minutes. The thinnest and central pachymetry were continuously monitored through the procedure using Accutome AccuPach VI 24-6200 Pachymeter Digital Signal Analysis (Accutome, Inc, USA). Eyes with a pre-operative Central corneal thickness between 330 and 400 μm, application of a hypo-osmolar riboflavin for 5 minutes (1 drop every 20 second) was performed until adequate corneal thickness was reached (>400 μm).17
After treatment, gatifloxacin 0.5% (Zymaxid®; Allergan, Inc.) eye drops were instilled, followed by the placement of a bandage soft contact lens (ACUVUE®, Johnson & Johnson Vision Care, Inc.) for 5 days. Postoperatively, patients were given gatifloxacin 0.5% four times daily for 7 days, Tobramycin-dexamethasone 0.1% (TOBRADEX® Alcon Laboratories, Inc) four times daily for 10 days, followed by Loteprednol (LOTEMAX® Bausch & Lomb .Inc) 0.5% 5 times daily, tapered over 5 weeks. 11
Some patients in both groups were subject to combined procedure, ICRS and PRK. ICRS (Intacs® Addition Technology™, Inc) were implanted 4 weeks prior to CXL in both group if the patient had a decreased CDVA (<20/30) , contact lens intolerance and irregular astigmatism on topography. A total of 57 eyes were implanted with ICRS using Intralase femtosecond laser (IntraLase, Abbott Medical Optics Inc., Santa Ana, California, USA) to create the tunnels at 400µm depth (different ring segment arc length and thickness were used following our published algorithm in each case21). Also, a simultaneous PRK using eximer laser (ALCON WAVELIGHT® EX500 Alcon Laboratories, Inc.) was performed at the same day prior to CXL if the patient had a CDVA > 20/30, a minimum preoperative thinnest pachymetry of 480µm and a calculated ablation depth limited to <50µm over the cone. The 9 mm central corneal epithelium was removed using a blunt spatula. PRK was performed on 40 eyes. (Figure 1)
Data collection and Outcome Measures
Patients’ charts were reviewed. Assessment of their uncorrected distance visual acuity, corrected distance visual acuity (CDVA) and manifest refractions using Snellen charts was performed preoperatively, 6months, 1 year and 3 years post treatment. Logarithm of the minimum angle of resolution (logMAR) system was used to document and analyze visual acuity.
Also, slit lamp exam, fundus evaluation and corneal tomography maps were performed during each visit. The WaveLight® Allegro Oculyzer™ (WaveLight, GmbH, Erlangen, Germany) was used to record keratometry (K1, K2, K mean, K max) and pachymetry.
Statistical analysis
SPSS 19.0 (SPSS, Inc, Chicago, IL) was used to analyze data. Continuous variables (visual acuity, spherical equivalence, keratometry, pachymetry) were analyzed as mean and SD (standard deviation), while categorical variables (gender, ICRS, PRK) were presented as percentages. The progression rate was calculated for both keratoconus and ectasia. Pared sample t-test was used to explore relationships between continuous variables while chi-square test (Fisher's Exact Test) was used to compare categorical variables and progression rate. p-value was considered significant if less than 0.05.