Monika Jha, B.Optom

Fellow Optom (Retina), Dr. Shroff’s Charity Eye Hospital, New Delhi, India

Ophthalmic imaging modalities have revolutionised the field of eye care in ophthalmology by taking diagnostics to the next level. Various ophthalmic diagnostic modalities are used for the detection and confirmation of posterior segment disorders such as optical coherence tomography (OCT), OCT-Angiography (OCT-A), Fundus photography (FP), Fundus Fluorescein angiography (FFA) and Indo-cyanine green angiography (ICGA).

FFA and OCT-A are the two most used posterior segment diagnostics that help in the study of retinal vasculature in several posterior segment disorders.

FFA is the most used and most accurate posterior segment diagnostic imaging for the study of vascular disease of the retina. It is an invasive procedure that requires capturing a series of sequential photographs of the retinal vasculature following the intravenous injection of the fluorescein dye. It provides detailed information on the anatomy and physiology of retinal and choroidal circulation and helps in the confirmation of retinal diagnosis and in making an effective treatment plan for retinal disorders. FFA has several side effects like vomiting tendency, nausea, dizziness, skin rashes, difficulty in breathing, etc. ⁽¹⁾

OCT-A is a non-invasive diagnostic imaging technique, based on the principle of motion contrast which does not require the injection of any contrast agents. It especially gives volumetric information and has the capability to localise the pathology by providing structural and blood circulation information together.⁽²⁾

Retinal disorders affect the different parts of the retina, mostly the blood circulation of the retina resulting in vision loss. Choroidal neovascular membranes (CNVM) is a retinal disorder with an abnormal new growth of vessels in the choroidal capillaries which are fragile and immature and tend to break easily resulting in leakage in the macular region and thus leading to vision loss.⁽³⁾

In CNVM, the patient complains of sudden painless vision loss especially central vision, distorted vision, loss in colour brightness, different image size with different eyes, flashes of light (mostly myopic patient) and Scotoma in chronic cases. Most common form of CNVM is Wet age-related macular degeneration.⁽⁴⁾

FFA and OCT-A are the two important diagnostic tools for the ophthalmologists for the confirmation of diagnosis of CNVM.

Two most useful segments to visualise for changes in eyes with CNVM are:

1. Retina – (Outer plexiform layer- Bruch membrane)
2. Choriocapillaris (Region just below RPE 20 microns thick)

What to look for when diagnosing CNVM in OCT-A? ⁽⁵⁾

• Neovascular complex between Bruch’s membrane of choroid and RPE.
• Neovascular tissue that grows in the blood vessels of the choroid and penetrates the subretinal space through the RPE – Bruch membrane complex.
• Bleeding to correlate with OCT-A as intraretinal anastomoses occurring in deep retinal capillary plexuses as intraretinal and sub retinal miniatures.

Figure 1: shows Branch like neurovascular structure in Choroid plexus

Figure 2: Shows Net like neurovascular in Outer retina to choriocapillaris

What to look for diagnosing CNVM in FFA?

• Window defects
• Granular inactive hyper fluorescence
• Active pinpoint RPE leaks
• Diffuse leakage of dye in late phase without or with underlying focal RPE leaks.
• A stippled early hyper fluorescence without progressive leakage
• Retinal Pigment Epithelial Dystrophy (RPED)
• Ink blot /smokestack pattern of dye leakage

Figure 3 : Showing B-scan OCT shows Neovascular membrane in Bruch membrane and RPE which declare CNVM

Figure 4: This above picture shows window defect along with CNV at macular region

Can OCT-A be an alternative to FFA in the confirmation of diagnosis of CNVM?

FFA is the gold standard posterior segment diagnostics for the confirmation of CNVM.  As FFA is an invasive procedure and is contraindicated in case of pregnancy, Kidney problem or any previous allergy to fluorescein dye. So, in such cases we can look for OCT-A scans for neovascular complex between the RPE and Bruch’s membrane which is ordinarily devoid of blood flow in normal eyes and a branching neovascular network within the outer retina which aids in the confirmation of CNVM.⁽⁶⁾

However, OCT-A is limited to static flow of blood vessels rather than dynamic flow as in case of FFA. We will be able to see the branch vascular networking (BVN) due to the neovascular complex between Bruch’s membrane of choroid and RPE but will not be able to see the RPE leakage. Also, OCT-A is associated with many artefacts (due to blinks, movement or vessel ghosting).

There, OCTA and FFA both have their own significance along with their limitations. Ophthalmologists can use both the diagnostics tools for the confirmation of CNVM depending upon the condition and past ocular as well as systemic history of the patient.

Reference:

1. Fluorescein Angiography and Optical Coherence Tomography Correlation in Various Retinal Diseases.Jay Chhablani, MD, and Aditya Sudhalkar, MD
2. Koushik Tripathy, MD (AIIMS), FRCS (Glasgow) Andrea Tamine Hoyos Dumar, MD Diana V. Do, MD Talisa de Carlo, MD Jennifer I Lim MD CNVM OCTA findings
3. Gomolin J. E. (1989). Choroidal neovascularization and central serous chorioretinopathy. Canadian journal of ophthalmology. Journal canadien d’ophtalmologie, 24(1), 20–23.
4. Bhatt, N. S., Diamond, J. G., Jalali, S., & Das, T. (1998). Choroidal neovascular membrane. Indian journal of ophthalmology, 46(2), 67–80.7. International Journal of Retina and Vitreous
5. Choroidal Neovascularization: OCT Angiography Findings https://eyewiki.aao.org/User:Andrea.Tamine.Hoyos.Dumar.
6. Bansal, R., Dogra, M., Mulkutkar, S., Katoch, D., Singh, R., Gupta, V., Dogra, M. R., & Gupta, A. (2019). Optical coherence tomography angiography versus fluorescein angiography in diagnosing choroidal neovascularization in chronic central serous chorioretinopathy. Indian journal of ophthalmology, 67(7), 1095–1100. https://doi.org/10.4103/ijo.IJO_1238_18 .

Image Courtesy: The retinal scan images used in this blog were taken from Dr.Shroff’s Charity Eye Hospital, Daryaganj, New Delhi