original article

This retrospective nonrandomized open label study with consecutive recruitment comprised patients with the following inclusion criteria:
• Progressive keratoconus
• Corneal thickness of at least 400 µm
• No slit-lamp evidence of corneal scarring

Progression was defined as an increase in maximum keratometry (K) of 1.00 diopter (D) in one year (used from other studies of Caporossi et al., measured in the topographyimage as the steepest point), patient reports of deteriorating best corrected visual acuity (BCVA)[17,18] (excluding other possible non-cornea-related reasons for deterioration), or the need for new contact lens Þ tt ing more than once in two years.[19] Ultrasonic pachymetry was used with 9 points being measured in each eye (PalmScan, Micro Medical Technologies, USA). The apex was measured by collating the cone location magnitude index (CLMI) (Keratron Scout, Optikon, Italy)) from the corneal topography (Keratron Scout, Optikon, Italy). The CLMI is a soft ware built into the Keratron Topographer, and is based on the concept of locating the center of the cone and its magnitude. The algorithm is designed to determine the steepest 2-mm diameter circle within the central 8 mm of the topography. The area-corrected average of all points outside of the circle is ubtracted from the corrected average of all the points within the circle. This is repeated for the circle 180° away. The results are compared to decide if the area is a cone.

All patients or the legal guardians (in case of patients less than 18 years of age) provided informed consent aft er receiving a detailed description of the nature of the treatment. Patientsless than 18 years of age were also included in our study as the occurrence of keratoconus is seen at a much earlier age and with rapid progression in the Indian subcontinent.^[20] This study was performed in the city of Mumbai in western India.

The cross-linking was performed in the daycare facility of the Clear Vision Eye Center, Mumbai, India. Aft er topical anesthesia of propracaine hydrochloride 0.5% eye drops was administered, the epithelium was removed using a blunt spatula in a 9.0 mm diameter area. This was to ensure that the riboß avin penetrated the stroma and that a high level of UVA absorption was achieved. As a photosensitizer,0.1% riboß avin solution was applied to the cornea every 5 min for 25 min before the irradiation to allow suffi cient saturation of the stroma.^[20] Next, an 8.0-mm diameter of central cornea was irradiated with UVA light with a wavelength of 370 nm and an irradiance of 3 mW/cm2. The CBM (Caporossi, Baiocchi,Mazzott a) X Linker (CSO, Italy), was used as the UVA radiation source. This crosslinker has Þ ve pre-focused diodes with a LED divergence of 10° to provide a homogenous UVA radiation. During the 25 min ofirradiation,^[2] drops of 0.1% riboß avin solution (Ricrolin, Sooft Italia) were applied to the cornea every 5 min to sustain the necessary concentration of the riboß avin.

Aft er the treatment, the eyes were patched for 24 h. On removal of the patches the patients were instructed to use 0.5% moxiß oxacin eye drops (Alcon Laboratories, India), 1% prednisolone acetate eye drops (Allergan India) and tears naturale II (Alcon Laboratories, India) for a period of one week. All drops were recommended for use at four times daily.

Follow-up examinations were performed on day 1 and 3 or until complete re-epithelialization. Subsequent examinations were at one, three, six, and 12 months and then advised annually. At each examination, refraction, BCVA (Snellen Vision Charts) with glasses or with contact lenses, corneal topography (Keratron Scout, Optikon, Italy), central corneal thickness (CCT) (PalmScan, Micro Medical Technologies, USA), and intraocular pressure (IOP) (Goldmann applanation tonometer, Haag Streit, Switzerland) were recorded.

To quantify the cross-linking eff ect, the maximum K value of the apex, maximum and minimum K values in the 3.0 mm zone topography, astigmatism, and BCVA were recorded.

The changes were estimated by subtracting each parameter at the respective follow-up examination from the records prior to the day of cross-linking. Statistical evaluation was performed by analysis of variance (ANOVA) using JMP 4.0 soft ware.

Results : Only patients with a minimum follow-up of 12 months were included in the study. Thirty-seven eyes of 25 patients with a mean age of 16.9± 6.35 years (range 12-39 years) were included. The follow-up ranged from 12 to 16 months. The preoperative apex K value determined with the CLMI was 64.79 ± 7.22 D, the mean maximum keratometry was 53.26 ± 5.93 D (The apex values
were determined using the CLMI method used in Keratron Scout, Optikon, Italy and the maximum K was computed using the Simulated K values method. Thus the apex is higher than maximum K), the mean astigmatism was 7.24 ± 4.67 D (this obtained from the topography derived K). BCVA was 0.34± 0.30 (vision was recorded by Snellen’s and converted to decimal format for statistical calculations). Ultrasonic pachymetery (apex as determined by the topography and approximated to the eye) (Palmscan, Micromed Technologies, USA) was done in all eyes preoperatively to assess suitability and was 478 ± 45 µm.

An evaluation of 37 eyes in which stable parameters were recorded and the preoperative values on the day of treatment were compared with postoperative values of the 12-month examination showed that BCVA improved at least one line in 54% (20/37) of eyes and remained stable in 28% (10/37) of eyes (P=0.006). Astigmatism decreased by a mean of 1.20 D in 47% (17/37) of eyes (P=0.005) and remained stable (within ± 0.50 D) in 42% (15/37) of eyes. The K value of the apex decreased by a mean of 2.73 D in 66% (24/37) of eyes (P=0.004) and remained stable (within ± 0.50 D) in 22% (8/37) of eyes. The maximum K value decreased by a mean of 2.47 D in 54% (20/37) of eyes (P=0.004) and remained stable (within ± 0.50 D) in 38% (14/37) of eyes [Table 1].