Age-related macular degeneration ( AMD) is a disease affecting the macula, the central area
of the retina. There are two main types of AMD. Geographic atrophy ( dry) AMD and neovascular
( wet) AMD. In neovascular AMD, subretinal neovascular membranes develop beneath the retina.
The new vessels can leak causing haemorrhage that leads to edema, scarring and significant
visual loss. Sub-retinal neovasular membranes are defined as classic, occult and minimally
classic according to their apperance on fluorescein angiography. Trials have shown that early
laser photocoagulation of classic extrafoveal lesions could delay the loss of vision in a
small number of patients. However, most patients present with subfoveal membranes and whilst
photocoagulation can limit the extent of subsequent visual loss, it causes immediate loss of
central vision due to concurrent destruction of the overlying retina. Photodynamic theray (
PDT) represent a milestone in the treatment of CNV, and marks the start of a new era. Current
PDT operates on the basis of principal that makes use of a dye ( verteporfin) which is
preferentially retained in proliferating tissue such as CNV, sensitizing the endothelial
cells to laser rediation ( 689 nm). Endothelial cells degeneration is mediated by reactive
oxygen which intermediates with subsequent platelet activation, and a thrombosis, and
temporary or permanent occlusion of vessels is seen in the treated area ( Ghazi et al 2001.
The light is strong enough to activate the chemicals, causing them to emit free radicals that
destroy the blood vessles, but not strong enough to cause damage to the overlying retina. The
duration of the treatment is 83s. PDT is effective in predominantly classic subfoveal CNV,
but was observed to yield no visual benefit in minimally clasic CNV during a 2-year
follow-up. As to occult CNV PDT was effective in small lesions ( 4 disc areas or less), when
there was a recent disease progress and when visual acuity was less then 20/50. In the VIP (
Verteporfin Therapy of Subfoveal Choroidal neovascularization, 2 year resulta of Randomized
Clinical trial incl Lesion with Occult with no classic CNV) the primary outcome, visual
acuity, was similar for the verteporfin-treated and the placebo-treated eyes through the
month 12 examination. Between the month 12 and 24 rxminations, the treatment benefit grew so
that by the month 24 examination, the verteporfin-treated eyes were less likely to have
moderate or severe vision loss. PDT does have its drawbacks, ont is the cost. Another that
the patient become highly sensitive to strong light and needs to wear special sunglasses for
48 hrs after treatment. There has also been discussions regarding lesion size and the
potential of damage due to re-treatments.
Transpupillary thermotherapy ( TTT) is a thermic teratment of CNV in AMD. Using a thermal
diode laser ( emission 810nm), transpupillary irradiation of the fundus through a
conventional ( laser) contact lens is performed. The irradiation is resorbed mainly in the
melanin granules of RPE and choroidal melanocytes and there is little absorption in the
neurosensory retina. The temperatures in the layers of RPE and choriocapillaris is elevated <
10 degrees C during a 60s exposure to continuous rediation. High rates of resportion of the
radiation in the endothelium of growing, newly formed vessels will result in thrombus
formation and delayed closure of the CNV. The power is adjusted to the diameter of the laser
beam. Laser power of 400 mW for a 2.0 mm spot, was found to be safe for the retina in human
eyes ( Conolly et al 2001). In a pilot study, Reichel et al ( 1999) demonstrated that
subfoveal occult CNV could be occluded and visual acuity stabilized in a majority of patients
treated with TTT. These results has been confirmed in small series of cases.
This prospective, randomized controlled study aim to compare PDT and TTT as a treatment for
occult and minimally classic CNV. A total of 140 patients will be included in the study, (
110 patients are presently included). Follow up is 2 years. The main outcome is visual acuity
( ETDRS), new vessel growth ( fluorescein angiography and ICG), retinal thickness ( OCT.
Furtermore patients will participate in a quality of life questionnarie ( National Eye
Institute Visual Function Questionnarie, NEI-CFQ-25).