New Laser Treatment Options in Age-related Macular Degeneration: Transpupillary Thermotherapy
Age-related macular degeneration (ARMD) is the leading cause of legal blindness in the developed countries (22, 24). The deterioration of central visual acuity, the development of metamorphopsia and a central scotoma lead to a reduction of patients' reading capacities, which can extend to a threatening degree even in early stages. A consequence of this loss of vision can be social dependence, demonstrating the enormous social importance of ARMD (19). Depending on the clinical presentation, two different main forms may be distinguished: a dry and a wet form (63). The first one is characterized by an accumulation of debris in the different layers of the retinal pigment epithelium, called drusen, which may be miliar, serous or confluent, basic laminar or linear, finally leading to a rarefaction of the retinal pigment epithelium, in form of areolar or geographic atrophy.
The genesis of the disease is considered to be multifactorial, genetic factors interfering with regulatory functions of the retinal pigment epithelium seem to be involved (64).
By lesions of Bruch's membrane or the pigment epithelium, choroidal neovascularizations (CNV) may sprout underneath the retinal pigment epithelium or the sensory retina (4, 5, 6, 46). Two different angiographic features must be distinguished: a classic form with a well demarked border of the CNV and an occult form, which shows late leakage from hyperfluorescent lesions, detachment of the retinal pigment epithelium with notches or “pin points”. This may lead to extravasation of liquid, to intra- and subretinal hemorrhage and, in the end, to a fibrotic destruction of the retina, resulting in a scar. Characteristically, these CNV are localized directly under the macula, particularly under the foveal avascular zone (21, 55). Thus, therapeutic options like laser coagulation and surgical interventions are limited. Furthermore, the surgical interventions like CNV excision, macular translocation or transplantation of the retinal pigment epithelium are still at an experimental stage (52).
Apart photodynamic therapy, which uses a photosensitizing agens, transpupillary thermotherapy is a new and noninvasive method to treat choroidal neovascularization. Based on a low grade hyperthermia, mostly sparing the surrounding tissue, laser light derived from an infrared diode laser at 810 nm is used to apply long pulse spots of 60 seconds of duration. Energy is chosen depending on the spot size 509 mW (spot: 2000 μm) and 800 mW (spot: 3000 μm), respectively.
At the time of diagnosis, 8% of the patients suffer from bilateral disease. If the degeneration is unilateral, the risk for the fellow eye amounts to 10–12% per year (4, 13, 23).