Dr. Arpltha Pereira, Dr.Santosh Gopi Krishna Gadde, Dr.Naresh Kumar Yadav, Dr.Rohit Shetty
Introduction
Idiopathic polypoidal choroidal vasculopathy (IPCV) is a pathology of the choroidal vasculature characterized by. In 1989, Yannuzzi and colleagues first described idiopathic polypoidal choroidal vasculopathy in 11 patients with subretinal, vascular lesions associated with serous and hemorrhagic detachments of the retinal pigment epithelium (RPE)1,2.
The etiology and pathophysiology of IPCV is not clearly understood but there is a propensity for dilation and aneurysmal formation of choroidal vasculature3,4.
Though history and clinical examination are first steps in diagnosis, Indocyanine green angiography is currently the gold standard in diagnosis of IPCV. In 1995, Spaide and colleagues identified the precise choroidal abnormalities associated with PCV and examined them usingICGA5. It showed two basic choroidal vascular changes: a branching network of vessels in the inner choroid and polypoidal vascular dilations at the border of the network of vessels.
Based on ICGA features IPCV has been divided into 2 types: a.)Type 1 (polypoidal CNV): polyp/s with well-defined branching vascular network (BVN, both feeder and draining vessels), b.)Type 2 (typical PCV): polyp with absent BVN (neither feeder not draining vessels)6,7. Still ICGA cannot completely differentiate some pathologies like central serous chorioretinopathy from IPCV as both conditions share the same pachychoroid spectrum.
Thus ICGA is aided in diagnosis by Optical coherence tomography (OCT). It helps in identification of subretinal or sub-RPE fluid, and can also delineate polypoidal lesions. These lesions resemble dome-like elevations of RPE with moderate internal reflectivity. In most cases, there is also a highly reflective line just below these lesions consistent with location of vascular branching network8. The dual reflective layers are also called “double-layer sign,” and are seen in 59% of eyes with PCV9. Thus, ICGA and OCT, both are useful for understanding the pathophysiology and for diagnosing PCV. However, the cause and the pathogenesis of PCV are not clearly known.
OCTA is a non-invasive technique that acquires volumetric angiographic information without the use of dye. Each three-dimensional scan set takes approximately six seconds to obtain. The en-face images (OCT angiograms) can then be scrolled outward from the internal limiting membrane (ILM) to the choroid to visualize the individual vascular plexus and segment the inner retina, outer retina, choriocapillaris, or other area of interest. The en-face acquisition areas currently range from 2 × 2 mm to 12 × 12 mm with the scan quality greatly decreased with a widened field of view since the same number of OCT b-scans is used for all scanning areas. The 12 x 12 mm scan is only available on research prototypes. The 3 × 3 mm OCT angiograms appear to be higher resolution than the currently available FA/ICGA images. Therefore, OCTA provides both structural and functional (i.e. blood flow) information in tandem10.
However, OCTA is more prone to artifact than FA or ICGA. Because OCTA uses the principle that movement in the back of the eye represents blood flow, it is prone to motion artifact. OCTA can also miss areas of slow blood flow such as in microaneurysms or fibrotic CNV. Since OCTA relies on change between consecutive b-scans, it will detect flow only above a minimum threshold, the slowest detectable flow, which is determined by the time between the two sequential OCT b-scans. Lesions that have flow below the slowest detectable flow would therefore not be visualized using this imaging technique.
Thus, we through this study would like to know if OCTA can be used as a novel diagnostic tool with ICGA for understanding a pathological process like IPCV, where neovascular changes occur at different levels of choroidal vasculature.
Methodology
In this study , 51eyes having ICG diagnosed PCV with BVN were recruited and subjected to 3×3, 6×6, 8×8 scanning protocols of OptovueAngiovue OCTA. The area of BVN on OCTA and on enface OCTA was calculated and co related with that of ICG using image J software.The en face images were analysed by two users independently and compared with the ICGA images to remove intraobserver bias.
Results
The study included 51 eyes of 51 patients diagnosed as having IPCV with BVN on ICGA which underwent OCTA scans. The characteristics of study population is shown in Table 1.
| Characteristics | Value |
| Age (years) | 64.8 ± 8.46 |
| Sex
Males Females |
32 (52.4 %) 29 (47.6 %) |
| Eye laterality
Right Left |
27 (44.3 %) 34 (55.7 %) |
| BCVA (log MAR) | 0.67 ± 0.49 |
| IOP (mmHg) | 14.35 ± 3.26 |
The mean follow up for the patients was 24.69 ± 16.11 months (range being from 2 to 60 months).
The characteristics of IPCV illustrated on ICGA imaging at initial visit are shown in Table 2.
| Characteristics | Value |
| Number of Polyps
Less than 5 More than 5 |
46 (75.4 %) 15 (24.6 %) |
| Location of Polyp
Macular Extramacular Peripapillary |
41 (67.2 %) 19 (31.1 %) 10 (16.4 %) |
| Size of BVN
Less than 1 DD 1 DD More than 1 DD |
27 (44.3 %) 4 (6.5 %) 30 (49.2 %) |
| Foci of BVN
Single Multiple |
53 (86.8 %) 8 (13.2 %) |
| Shape of BVN
Prominence Fine net Sea fan |
25 (41 %) 32 (52.4 %) 11 (6.6 %) |
| Feeder vessels
Present Absent |
12 (19.7 %) 49 (80.3 %) |
At final visit, ICGA of 34 of the initial subjects showed regression of polyps in 15 (44.1 %) cases.
The polypoidal lesions were detected in 51 eyes (83.6 %) byen face OCT. Manual segmentation was required to detect the pathologic lesions of PCV in all cases. From analysis of images combined from different layers, polyps could be seen singly as well as differentiated from overlying pigment epithelial detachment. The BVNs could be clearly delineated and the size could be measured us. Out of the 34 eyes seen on long term follow up, 13 cases showed decrease in size of BVN from initial visit. This was correlating with regression detected on ICGA. Also, BVN were prominently seen on CC slab of OCTA.
Discussion
This study compared the angiographic features of IPCV detected by ICGA anden face OCTA. Our results demonstrated that the detection rate of the polypoidal lesions as well as BVN were significantly high by en face OCTA comparable with ICGA. The detection rate of en face OCTA was around 84 % for polypoidal lesions. It could clearly delineate polypoidal lesions even with overlying PEDs.
The cases where polyps were missed might be due to poor blood flow in the polyp, since OCTA can detect the blood flow, but not the vessels themselves. Also anti-VEGF treatment or photodynamic therapy induces the regression of the polyp, the previous history of treatment might reduce the detection rate by OCTA. Another point is that staining or pooling of ICGA dye around the polyps enhances the visualization of the polyps in ICGA in the late phase.
Because we can evaluate the polypoidal lesions and the BVN at each clinical visit, using OCTA without dye injection might be useful to monitor the progression or recurrence during follow-up. However, ICGA would still be necessary in diagnosing PCV, since the detection rate of the polypoidal lesions was significantly low by OCTA compared with ICGA.
Conclusion
En face OCTA enabled us to analyze the angiographic features of PCV combined with OCT B-scan. Indocyanine green angiography will still be necessary to make the diagnosis of PCV. En face OCTA may be useful for understanding the pathogenesis of PCV and managing PCV.
References
- Yannuzzi LA. Idiopathic Polypoidal Choroidal Vasculopathy. Presented at: Macula Society Meeting, February 5, 1982, Miami, FL, USA.
- Yannuzzi LA, Sorenson J, Spaide RF, Lipson B. Idiopathic polypoidal choroidal vasculopathy (IPCV). Retina 1990; 10:1–8.
- Maruko I, Iida T, Saito M, et al. Clinical characteristics of exudative age-related macular degeneration in Japanese patients. Am J Ophthalmol 2007; 144:15–22
- Imanmura Y et al. Polypoidal Choroidal Vasculopathy: A Review. SurvOphthalmol 2010; 55:501–515.
- Spaide R F, Yannuzzi L A, Slakter J S. et alIndocyanine green videoangiography of idiopathic polypoidal choroidal vasculopathy. Retina 199515100–110.
- Kawamura A, Yuzawa M, Mori R, Haruyama M, Tanaka K. Indocyanine green angiographic and optical coherence tomographic findings support classification of polypoidal choroidal vasculopathy into two types. ActaOphthalmol. 2013 Sep;91(6):e474-81
- Honda S, Matsumiya W, Negi A. Polypoidal choroidal vasculopathy: clinical features and genetic predisposition. Ophthalmologica. 2014;231(2):59-74.
- Kamaeda T, Tsujikawa A, Otani A, et al. Polypoidal choroidal vasculopathy examined with en face optical coherence tomography. Clin Experiment Ophthalmol. 2007; 35(7):596-601
- Sato T, Kishi S, Watanabe G, et al. Tomographic features of branching vascular networks in polypoidal choroidal vasculopathy. Retina. 2007 27; 589-594.
- Matsunaga D, Puliafito CA, Kashani AH. OCT Angiography in Healthy Human Subjects. Ophthalmic Surg Lasers Imaging Retina. 2014;45(6):510–5.
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