Optical coherence tomography in photodynamic therapy for subfoveal choroidal neovascularisation secondary to age related macular degeneration: a cross sectional study

Abstract

Aims: To introduce new terminology and validate its reliability for the analysis of optical coherence tomography (OCT) scans, compare clinical detection of cystoid macular oedema (CMO) and subretinal fluid (SRF) with OCT findings, and to study the effect of photodynamic therapy (PDT) on the foveal morphology.

Methods: Patients with subfoveal, predominantly classic choroidal neovascularisation (CNV) secondary to age related macular degeneration (AMD) undergoing PDT were evaluated with refraction protocol best corrected logMAR visual acuity (VA), slit lamp biomicroscopy, stereoscopic fluorescein angiography (FFA), and OCT. New terminologies introduced to interpret the OCT scans were: neuroretinal foveal thickness (NFT), bilaminar foveal thickness (BFT), outer high reflectivity band thickness (OHRBT), intraretinal fluid (IRF), subretinal fluid (oSRF), and vitreomacular hyaloid attachment (VMHA).

Results: Fifty six eyes of 53 patients were studied. VA was better in eyes with a thinner outer high reflectivity band (OHRBT) (p = 0.02) and BFT (p = 0.05). BFT was less in eyes that had undergone a greater number of PDT treatments (p = 0.04). There was poor agreement between OCT and clinical examination in the detection of CMO and subretinal fluid (kappa = 0.289 and kappa = 0.165 respectively). To validate the interpretation and measurements on OCT, two groups of 20 scans were analysed by two independent observers. There was good agreement between the observers in the detection of IRF, oSRF, and VMHA (p<0.001). Measurements of NFT and BFT had a high reproducibility, and of OHRBT reproducibility was low.

Conclusions: New terminology has been introduced and tested. OCT appears to be superior to clinical examination and FFA in the detection of CMO. In this study, better vision was associated with a thinner OHRBT and/or the absence of SRF giving insight into the biological effect of PDT.

Figure 1

Optical coherence tomogram passing through the fovea of a normal eye illustrating retinal layers and terminology developed for the study. RNFL, retinal nerve fibre layer; PRL, photoreceptor layer; RPE, retinal pigment epithelium; NFT, neuroretinal foveal thickness (distance between inner high reflectivity band and inner margin of outer high reflectivity band at foveal centre); OHRBT, outer high reflectivity band thickness; NFT = 181 μ and OHRBT = 58 μ in this scan.

Figure 2

(A) Colour fundus photograph of the right eye of an 83 year old male patient demonstrates a green-grey subfoveal lesion with haemorrhage. The arrow indicates the location and direction of the optical coherence tomographic (OCT) scan. (B) OCT image demonstrates loss of foveal depression with cystoid spaces and vitreoretinal hyaloid attachment. NFT, neuroretinal foveal thickness; OHRBT, outer high reflectivity band; IRF, intraretinal fluid. NFT = 406 μm and OHRBT = 307 μ in this scan.

Figure 3

(A) Colour fundus photograph of the left eye of a 54 year old female patient shows a subfoveal green-grey lesion with minimal haemorrhage. The arrow indicates the location and direction of the optical coherence tomographic (OCT) scan. (B) OCT passing through the fovea illustrating bilaminar foveal thickness (BFT), intraretinal fluid (IRF), and subretinal fluid (SRF). BFT is the distance between the inner high reflectivity band and the inner margin of the outer high reflectivity band at the foveal centre in the presence of subretinal hyporeflective area. NFT = 473 μ and BFT = 722 μ in this scan.

Figure 4

Relationship between bilaminar foveal thickness (BFT) and number of PDT application in 56 eyes. The linear regression line is y = −15.928x+231.14 (r = −0.275, p = 0.04).

Figure 5

Relation between visual acuity (logMAR letters) units plotted against outer high reflectivity band (OHRBT) in μm in 56 eyes. The linear regression line is y  = −2.3352x+350.58 (r = −0.331, p = 0.02).