Preservation of Vision
The chances of conserving vision depend on tumor size, location and extent as well as the therapeutic modality that is deployed and any iatrogenic morbidity that develops. It is important to distinguish between visual loss caused by the tumor itself and visual loss caused by the treatment.
After radiotherapy, visual loss can occur as a result of collateral damage to optic nerve, fovea, and lens or because of exudation from the irradiated tumor, which causes macular edema or hard exudates, serous retinal detachment and, in severe cases, neovascular glaucoma (ie, toxic tumor syndrome). The collateral damage depends on the proximity of the tumor to important ocular structures and the radiation dosimetry, with β-emitting plaques and charged particles causing less irradiation to healthy tissues than γ-emitting plaques[21,52,53] and with palladium having a shorter range than iodine-125.[24] The toxic tumor syndrome correlates mostly with tumor bulk and to some extent the radiation dosimetry, with exudation being less likely after ruthenium plaque radiotherapy because this delivers such a high dose of radiation to the tumor base, obliterating the tumor blood supply. Predisposing factors such as diabetes mellitus and systemic chemotherapy are also important.
The treatment of radiation-induced morbidity has improved in the recent years, with advances in antiangiogenic therapy and a better understanding of the pathophysiology, which has encouraged measures such as transpupillary thermotherapy, photodynamic therapy, and local resection of the irradiated tumor.
The visual outcome therefore depends not only on the type of treatment and the skill with which it is administered but also on the ocular and systemic factors present at the time of treatment as well as the success with which iatrogenic ocular morbidity is treated.[18,54–56] In the COMS, a randomized trial comparing enucleation and iodine-125 plaque brachytherapy, 43% to 49% of treated eyes had substantial impairment in visual acuity by 3 years after brachytherapy (loss of ≥6 Snellen lines from the pretreatment level) or visual acuity of 20/200 or worse (43% of eyes).[57] Patients with diabetes, thicker tumors, tumors close to or beneath the foveal avascular zone, tumor-associated retinal detachment, and tumors that were not dome shaped were most likely to have a poor visual acuity outcome within 3 years after plaque brachytherapy.[57] Visual outcomes are still being reported using Snellen charts. Damato[53] developed a quick method for measuring the Visual Acuity Rating, using LogMAR charts. This allows rapid and intuitive visual acuity measurements, which are more amenable to statistical analysis than Snellen acuity.
Int Ophthalmol Clin. 2015;55(1):23-43. © 2015 Lippincott Williams & Wilkins
