in recent years , corneal specialists have shown a fast growing interest in collagen crosslinking using the photosensitizer riboflavin and ultraviolet a light as a new therapeutic alternative for the treatment of progressive keratoconus .
the aim of this treatment is to modify the biomechanical properties of the cornea , thus increasing its rigidity and preventing the progression of keratoconus.1 promising results have been published recently , and data from the dresden clinical study have shown stabilization of the disease , even after 5 years.2,3 it is necessary to follow strict treatment settings and patient eligibility criteria to avoid serious ocular side effects .
the patient s cornea must be irradiated with a small peak - like sector of the ultraviolet a spectrum ( 370 nm ) with 3 mw / cm irradiance for 30 minutes , which corresponds to a dose of 5.4 j / cm.3 the ultraviolet a irradiance must be checked before each treatment using an ultraviolet a meter to ensure that the optimal irradiance dose is delivered .
the photosensitizing riboflavin 0.1% solution must be applied 5 minutes before irradiation and every 5 minutes during irradiation .
it is also essential to perform preoperative pachymetry on each patient to exclude those with extended areas of less than 400 m of stromal thickness .
we describe how to perform collagen crosslinking in the protocol setting using a slightly modified ultraviolet a dermatological lamp and preparing the riboflavin 0.1% solution inhouse .
we used a slightly modified 370 nm ultraviolet a lamp ( uv 109a , waldmann , villingen - schwenningen , germany ) designed for dermatological treatment ( figure 1a ) , covered with a black plastic adhesive tape leaving a small window through which ultraviolet light can reach the cornea ( figure 1b ) .
the desired irradiance of 3 mw / cm is tested with a ultraviolet a meter ( waldmann ) before each treatment , thus establishing the optimal distance from the ultraviolet a lamp to the cornea .
the lamp was held by a clamp mounted on an intravenous pole ( figure 2 ) .
patients corneas were irradiated with 3 mw / cm of ultraviolet a ( 370 nm ) for 30 minutes .
the riboflavin 0.1% solution was prepared just before treatment by mixing 10 mg of riboflavin-5-phosphate ( guinama , valencia , spain ) with 10 ml of dextran 20% solution .
the solution was introduced into an empty 15 ml balanced salt solution bottle ( alcon laboratories , fort worth , tx , usa ) wrapped in aluminum foil to avoid exposure of the riboflavin to ambient light ( figure 3 ) through a 0.22 m sterilization filter ( millipore corporation , bedford , ma , usa ) .
the riboflavin 0.1% solution was applied 5 minutes before irradiation and every 5 minutes during irradiation .
thus far , we have successfully treated 12 patients with progressive keratoconus using this ultraviolet a lamp and riboflavin 0.1% solution ( figure 4 ) prepared inhouse .
the riboflavin solution was also easily prepared in the clinical pharmacy of the hospital by trained personnel .
one important issue to be mentioned is the fact that the limbus should be protected against irradiation , and a round 8 mm hole in the tape that covers the lamp could be made for this purpose .
the price of a commercially available ultraviolet a lamp designed for collagen crosslinking is approximately  15,000 , and the riboflavin solution prepared inhouse costs approximately  60 per patient .
the price of the slightly modified ultraviolet a dermatological lamp we used is approximately $ 400 , the riboflavin 0.1% solution we prepared inhouse costs $ 2.20 per patient , and the ultraviolet light meter price costs around $ 200 .
this provides ophthalmologists worldwide with an affordable alternative device for collagen crosslinking , especially for those in developing countries or places where resources are limited .
 in this paper , we describe an original , affordable , and available device for performing collagen crosslinking . 
 this is carried out in a safe and reproducible way by means of a simple modification to an affordable ultraviolet a lamp and by preparing riboflavin 0.1% solution inhouse . 