Purpose: Validating the current protocol of Amsler chart grid surveillance for the early detection of subretinal neovascular membrane(SRN) in age-related macular degeneration(AMD), and investigating its value in facilitating early laser therapy.
Methods: A retrospective pilot study.
Setting: Central London eye hospital with dedicated 24-h ophthalmic casualty serving West and West-central London.
Participants: 100 consecutive AMD patients who attended casualty with vision loss fulfilling the following criteria: patients had received and been instructed in the use of Amsler charts according to the unit's dispensation protocol,fluorescein angiography which confirmed new SRN. Patients presented over 20 months. Outcome measures were detection of SRN by the Amsler chart, and laser treatment of SRN.
Results: The Amsler chart surveillance protocol had detected SRN in 29 of the 100 patients. The surveillance protocol detected less than 30% of the specific patients who subsequently underwent laser treatment. A statistically significant difference was seen on comparing the ages of patients in whom the screening protocol was successful versus those in whom it was unsuccessful (student's t-test,P<3.2 x 103). Younger patients were more likely to be detected using the Amsler chart. A one-tailed Z2 test approached, but did not achieve, statistical significance (Z2 = 1.057,P <0.3) suggesting that patients who have already lost vision to SRN in one eye might not be more likely to be detected using the surveillance protocol than patients in whom SRN was affecting their first eye. In all, 38% of surveillance responders went on to receive laser therapy, compared with 37% of surveillance nonresponders.
Conclusions: The current Amsler chart surveillance protocol is suboptimal for detecting SRN in AMD, and a proportion of cases suitable for early laser therapy may be missing rapid detection. The results are especially important since recent advances in laser therapy for SRN require early detection for optimal effectiveness.