Ophthalmic complications of radiation therapy of tumors of the head in dogs and cats.

Abstract

Irradiation is an important part of the therapy for nasal, paranasal, and brain tumors, and is becoming increasingly available in veterinary medicine. The goal of irradiation is to induce an increased degree of cell death inside the tumor, while minimizing side effects. The eye is sensitive to acute as well as to late complications. In this article the literature on ophthalmic complications of irradiation is summarized. The aim of this descriptive study was to investigate the incidence and nature of ophthalmic complications in 15 patients of the Utrecht University Clinic for Companion Animals in The Netherlands and to compare these to the complications described in literature. The research consisted of a retrospective part (late complications, in patients treated between July 2010 and March 2014), and a prospective part (acute complications, in patients treated between March and June 2014). During the research period (March 10th 2014 to June 30th 2014), a questionnaire was completed by 15 patient owners, of which seven patients were invited for ophthalmic examination. Of four of the remaining eight patients, information on ophthalmic examination was derived from the patient file. Ophthalmic examination took place prior to the start of radiation therapy (n=3), and at three time points after irradiation (at the last day of radiation treatment (n=6), at 2-4 weeks after treatment (n=8), and at 15-49 weeks after treatment (n=3)). At the first post-therapy examination, only mild acute responses were seen (n=4/6). The acute reactions mainly consisted of conjunctival hyperemia and epiphora. In two patients signs had progressed by the second post-therapy examination. Corneal edema (n=5/8), epiphora (n=5/8), conjunctival hyperemia (n=5/8) and keratoconjunctivitis sicca (KCS, n=1/8) were seen. One patient showed bilaterally moderately swollen eyelids at the first post-treatment examination, which unilaterally progressed to severely swollen eyelids at the second post-treatment examination. One patient with no vitreal liquefaction at the first post-treatment examination had developed moderate vitreal liquefaction at the second examination. Two patients had KCS (n=2/3) at the third post-treatment examination. Non-progressive cataract was seen in two patients. By the third post-therapy examination, complete loss of vision had occurred in one patient (n=1/3), with retinal hemorrhages in the left eye and complete retinal detachment in the right eye. One of the other patients also showed small retinal hemorrhages, without impaired vision. Taken into account the length of the period between exposure to radiation and the clinical occurrence of late complications, this research was only a preliminary study. Further research with more patients and longer follow-up times is necessary to determine precisely which acute and late ophthalmic complications of cranial radiotherapy occur in canine and feline patients of the Utrecht University Clinic for Companion Animals, and which additional preventive measures could help in reducing the occurrence and severity of acute and late complications.