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FEEDER VESSEL TREATMENT IN AGE RELATED MACULAR DEGENERATION
NAZIMUL HUSSAIN, ANJILI HUSSAIN, S NATARAJAN
Aditya Jyot Eye Hospital, Aashirwad, 168D, Vikas Wadi, Dr. Ambedkar Road, Dadar TT, Mumbai - 400 014.
Feeder Vessel treatment is a recent treatment and a re-evaluation technique of previously abandoned procedure. Treatment entails proper identification of the FVs using Dynamic Indocyanine Green Angiography and maintaining for subfoveal choroidal neovascular membrane. The highlight of this technique is that it does not alter the natural history in patients with favourable outcome. However, this procedure requires further studies to establish the efficacy of the treatment.
INTRODUCTION
Neovascular age related macular degeneration is responsible for 90% of severe visual loss in 10-20% of blindness due to age related macular degeneration (ARMD). Exudative ARMD remains the leading cause of blindness in patients over the age of 55 years. Despite various therapeutic concepts under investigation, laser photocoagulation is still the acceptable means of treatment for patients with choroidal neovascularisation secondary to ARMD. Various single centre or multicentre national collaborative trials have studied the efficacy of laser treatment of well demarcated or so called classic choroidal neovascularisation (CNV). The management of subfoveal CNVM is still an unsolved problem. But, conventional laser treatment for subfoveal CNV could not prove its benefit as far as functional quality and recurrence of lesion is concerned. This is reluctantly accepted by the patients and ophthalmologists in the management of subfoveal CNV. Other alternative treatment such as surgical excision, perifoveal or grid laser treatment, radiation therapy and medical therapy could not also prove its benefit at this point of time.
However, TAP investigations has shown at the end of 24 months that photodynamic therapy with verteporfin can stabilize or improve vision in patients with subfoveal CNV secondary to ARMD where greatest linear dimension is no greater than 5400 microns. In an endevour to find technique to treat subfoveal CNV, a renewed interest of treating the extrafoveal photocoagulation of the feeder vessel (FV) has found its importance.
The extrafoveal laser photocoagulation for feeder vessel (FVs) giving blood supply to subfoveal CNV has been theoretically expected to be a method. The MPS guidelines have described laser treatment of FVs in addition to photocoagulation for all neovascular components of recurrent CNV with FVs. Malberg and Thomas also reported the successful laser photocoagulation of a FVs for recurrent subfoveal CNV after submacular surgery.
A feeder vessel is was defined as a vessel that was seen at the earliest phases of indocyanine green angiography (ICGA) and appear as a definite spot in the choroid and branch or after a course into the CNV with distinct blood vessel. In order to identify the feeder vessel, high speed ICG videoangiography (CSLO-ICGA) is necessary and various studies have also shown this potential. With CSLO-ICGA feeder vessel and its structure has been shown to occur in 20-30% of the patients with ARMD.
Hence, FV treatment is a two step process, consisting of FVs identification and photocoagulation of the FVs. Two patterns of FVs has been identiidentified:
1. Racquet like pattern
2. Umbrella like pattern
Racquet like pattern was found to be beneficial in complete occlusion as the length of the vessel was completely visible. Umbrella like pattern was found un-favourable as the FVs was masked by the membrane and only the cross section of the vessel was available for the treatment. Besides using conventional lasers (argon 532nm green, Dye laser) for photocoagulation, it has also been proposed to consider a different approach to reduce concomitant retinal tissue damage and safely target FVs closer to the fovea. Hence, ICG enhanced 810nm diode laser has also been proposed.
Successful obliteration of the FVs has been reported by various authors. Reported series enumerates 70-80% success rate of FVs closure. However, 1 or 2 retreatment was necessary. Final visual acuity of 20/100 or better was seen in 43% of the reported case series. Recurrence of CNV, mistaken identification of the FV and recanalisation after photocoagulation were considered to be the causes of anatomic failure. Recurrence rate was 19% within or apart from the neovascular lesion.
The prognostic factors were smaller CNV, shorter distance between the fovea and one lateral margin of the CNV, location of the FVs under the membrane and also narrowness of the treatable FVs. That, it preserves the possibility of other forms of treatment, does not interefere with the favourable natural history and does not create large areas of ischaemia adds to its major advantages to other forms of conventional treatment.
Postoperative complications noted were subretinal haemorrhage and choriocapillaries occlusion seen beneath the subfoveal CNV on FA. Recurrence was reported as 19% by Shiraga et al. MPS study guidelines reported that the feeder vessel usually extends from the laser scar to the area of adjacent CNV. It has recommended to treat the feeder vessel within the prior laser scar, and treat only the afferent side of the vasculature. Resolution of subretinal fluid and visual improvement typically follow within hours to weeks of closure. Recurrences are most likely within two months of treatment. Careful follow-up and repeat angiography are needed to make sure that there has been closure or significant delay in filling of the feeder vessel after treatment.
The most important advantage of FVs is that it preserves the possibility of other forms of treatment without interference with favourable natural history in case of a stable membrane. It does not create larger areas of ischaemia that may stimulate further neovascularisation. Hence this abandoned procedure, which showed fairly good results requires to be verified by means of adequate randomized clinical trial.
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