Chronic GVHD (cGVHD) is a predominant cause of mortality and disability not related to relapse; it occurs in 30 to 70% of patients. The majority of patients with cGVHD present with ocular involvement with a reported incidence of 40-60%. Symptoms can range from mild dry eye syndrome to severe epithelial defects that can generate corneal perforation and loss of vision. The most accepted pharmacological modality is the topical application of cyclosporine A; on the other hand, tacrolimus has shown greater immunosuppressive power when used in ocular GVHD. However, this effectiveness is limited since by the time the manifestations appear, there is already permanent damage to the lacrimal gland due to the lymphocytic infiltration; so it is necessary to use a prevention strategy before these manifestations appear. Previously, the employment of ocular cyclosporine drops as ocular GVHD prophylaxis was assessed to evaluate safety and effectiveness, showing that it is well tolerated and can limit the appearance of severe dry eye manifestations in a small group of patients. The purpose of this work is to compare the two modalities currently accepted for the treatment of the disease, but in a prophylactic way; topical ciclosporin A against topical tacrolimus, to determine the safety and efficiency of each of them as a preventive measure to limit the risk of developing the appearance of ocular cGVHD and the permanent consequences that this generates.