Ocular phototherapy

Abstract

Phototherapy can be translated to mean 'light or radiant energy-induced treatment.' Lasers have become the exclusive source of light or radiant energy for all applications of phototherapy. Depending on the wavelength, intensity, and duration of exposure, tissues can either absorb the energy (photocoagulation, thermotherapy, and photodynamic therapy (PDT)) or undergo ionization (photodisruption). For phototherapy to be effective, the energy has to be absorbed by tissues or more specifically by naturally occurring pigment (xanthophyll, haemoglobin, and melanin) within them. In tissues or tumours that lack natural pigment, dyes (verteporphin, Visudyne) with narrow absorption spectrum can be injected intravenously that act as focal absorbent of laser energy after they have preferentially localized within the tumour. Ocular phototherapy has broad applications in treatment of ocular tumours. Laser photocoagulation, thermotherapy, and PDT can be delivered with low rates of complications and with ease in the outpatient setting. Review of the current literature suggests excellent results when these treatments are applied for benign tumours, particularly for vascular tumours such as circumscribed choroidal haemangioma. For primary malignant tumours, such as choroidal melanoma, thermotherapy, and PDT do not offer local tumour control rates that are equivalent or higher than those achieved with plaque or proton radiation therapy. However, for secondary malignant tumours (choroidal metastases), thermotherapy and PDT can be applied as a palliative treatment. Greater experience is necessary to fully comprehend risks, comparative benefits, and complication of ocular phototherapy of ocular tumours.

Ultraviolet light-mediated drug delivery: Principles, applications, and challenges

“…Nowadays, coherent (lasers) and non-coherent (lamps and light emitting diodes, LEDs) light sources that emit across a wide range of the electromagnetic spectrum are widely available. Light has become an essential tool in many branches of modern medicine ranging from ophthalmology [12] to neurology. [13,14] However, exposure to UV light for extended periods can have deleterious effects on the skin, eyes and immune system.…”

Principles of Laser Therapy

“…Laser photocoagulation is used for a variety of chorioretinal diseases such as diabetic retinopathy, retinal tears or holes, age-related macular degeneration, and chorioretinal tumors such as retinal capillary hemangioma, choroidal hemangioma, and retinoblastoma [ 3 ].…”

“…Hemoglobin has a narrower range of maximum absorption that includes blue, green, and yellow wavelengths but excludes red wavelengths. Xanthophyll has maximal absorption limited only to the blue wavelengths [ 3 ]. …”

Non-Therapeutic Laser Retinal Injury

“…Tissue composition is also important in determining absorbance and resultant injury within specific layers of the retina [40] . ( Figure 3) Xanthophyll pigment is concentrated in the macula and has susceptibility to blue light damage due to its peak absorbance.…”

“…Argon and krypton wavelengths are primarily absorbed by hemoglobin and melanin, which then increase in temperature resulting in protein denaturation and tissue breakdown. Therapeutic applications of photocoagulative tissue injury include treatment of proliferative diabetic retinopathy, retinal vein occlusion, retinal capillary hemangioma, and choroidal tumors [59] .…”