Dear Editor,

Sahni et al. presented a new terminology to validate its reliability of optical coherence tomography (OCT) and studied the effect of photodynamic therapy (PDT) in patients with subfoveal, predominantly classic choroidal neovascularisation (CNV) secondary to age related macular degeneration (AMD) [1]. The new terminology introduced: neuroretinal foveal thickness (NFT), bilaminar foveal thickness (BFT), outer high reflectivity band thickness (OHRBT), intraretinal fluid (IRF), subretinal fluid (SRF), and vitreomacular hyaloid attachment. A heterogenous group of patients were included. Whereas in 3 patients OCT scanning was performed prior to PDT, 53 had already undergone up to 7 treatment sessions. The results showed a significant correlation of mean neuroretinal foveal thickness and intraretinal fluid. Additionally there was a high correlation between bilaminar foveal thickness and VA. The authors reported also a poor agreement between OCT and clinical examination in the detection of cystoid macular edema (CME) and subretinal fluid, indicating the usefulness of OCT.

We congratulate the authors and want to add two aspects from our clinical experience. In a previous study we reported the presence of CME and increased foveal thickness to correlate with a poorer visual outcome in non treated neovascular AMD [2]. Sahni et al. demonstrated no correlation of VA and IRF and SRF in patients undergoing PDT, giving evidence that a beneficial effect of PDT especially for the group of exudative AMD associated with CME arises. OCT seems to be valuable in predicting functional outcome following PDT.

The current study presented no data on the actual time when the OCT evaluation has been performed, although several authors described remarkable OCT findings following PDT. In a prospective study we evaluated 24 patients (53 PDT-sessions) prior to PDT as well as 2 days and 1 week after PDT by VA and OCT [3]. Herein a transient hyperopic shift corresponded with a consecutive increased retinal thickness up to 680µm on OCT. The cross-sectional OCT-scan in the macular area revealed a retinal detachment, whereas the anatomy of the neurosensory retina maintained intact, no relevant thickening or schisis-like changes were observed. Previous examinations by Costa et al. determined a few hours after PDT an increased subretinal leakage on indocyanine green angiography (ICG) and consecutive retinal elevation on OCT, confirming our functional and OCT- findings [4]. Long term OCT findings presented by Rogers et al., demonstrated structural alterations in terms of persistent retinal thinning 3 months after PDT [5]. Therefore OCT findings prior to the first PDT are necessary to determine predictable signs for functional outcome. OCT is a useful technique describing morphologic findings of the retina and choroid. Nevertheless, a higher number of patients prior to the first PDT application has to be evaluated by OCT to define predictable signs elucidating visual outcome.

Stefan Mennel, MD; Liu Fang, MD; Carsten H. Meyer, MD From the Department of Ophthalmology, Philipps-University, Robert-Koch- Str. 4, Marburg, Germany

References:

1. Sahni J, Stanga P, Wong D, Harding S. Optical coherence tomography in photodynamic therapy for subfoveal choroidal neovascularisation secondary to age related macular degeneration: a cross sectional study. Br J Ophthalmol 2005;89:316-320.

2. Ting TD, Oh M, Cox TA, Meyer CH, Toth CA. Decreased visual acuity associated with cystoid macular edema in neovascular age-related macular degeneration. Arch Ophthalmol 2002;120:731-7.

3. Mennel S, Hausmann N, Meyer CH, Hörle S, Peter S. Transient visual decrease after photodynamic therapy. Ophthalmologe. 2005;102:58-63.

4. Costa RA, Farah ME, Cardillo JA et al. Immediate indocyanine green angiography and optical coherence tomography evaluation after photodynamic therapy for subfoveal choroidal neovascularization. Retina 2003;23:159-165.

5. Rogers AH, Martidis A, Greenberg PB, Puliafito CA. Optical coherence tomography findings following photodynamic therapy of choroidal neovascularization. Am J Ophthalmol 2002;134:566-576.

Dear Editor,

We thank Mennel et al. and Duker et al. for their interesting comments regarding our article.

Mennel et al. make some interesting points on the immediate structural changes that occur after photodynamic therapy (PDT), a topic that we felt was outside the scope of our study. We agree that the short-term and long-term changes after treatment are important and need to be taken into account in future studies on patients undergoing PDT.

We are grateful to Dr’s Duker and Witkin for pointing out the article by Uchino and colleagues [1]. Our patients were older (mean 76 yrs [range 59- 94]) than those reported by these authors (mean 52.3 yrs). Uchino et al. had 20 patients in the same age group and only 2 patients were above 70 years of age. Both these had a complete posterior vitreous detachment (PVD). All our patients had associated pathology and majority had undergone PDT, all of which may have influenced the outcome. While the finding of vitreo-macular attachment may be more common in normal eyes (>50%), our study [2] suggests that the incidence may be may be lower in patients with exudative age-related macular degeneration (35.7%).

References

[1] Uchino E., A. Uemura, N. Ohba. Initial stages of posterior vitreous detachment in healthy eyes of older persons evaluated by optical coherence tomography. Arch Ophthalmol. 2001; 119:1475-1479.

[2] Sahni J, Stanga P, Wong D, Harding S. Optical coherence tomography in photodynamic therapy for subfoveal choroidal neovascularisation secondary to age related macular degeneration: a cross sectional study. Br J Ophthalmol. 2005; 89(3):316-320.