Microvasculature Dropout (MVD): A Novel Potential Marker in Diagnosing Glaucoma

Vaishaali Gunalan, M. Optom

Optometrist, Vision Care Centre, Lusaka, Zambia

MVD: What, where and how it is seen?

Optic nerve head (ONH) blood supply is “sectoral” in nature. Except for the surface nerve fibres, the rest ONH sectors are supplied by the “posterior ciliary artery (PCA)” ⁽¹⁾ (Figure 1). A decreased perfusion at any of this deep-layer microvasculature, especially near the β zone parapapillary atrophy adjacent to the optic disc is found to be a risk factor for glaucomatous optic neuropathy (GON), due to its vicinity to ONH and the common blood supply by short PCA.⁽¹⁾⁽²⁾ This sequence is called Microvasculature dropout (MVD).

Figure 1: A. Illustrates the ONH blood supply. B. Optic Nerve Head [Figure courtesy: Hayreh, S. S. (1996)]

MVD reflects the disruption of microvasculature in the prelaminar or laminar tissues.⁽³⁾⁽⁴⁾ It is measured as an angular extension, “angle α”.⁽⁵⁾ Optical Coherence Tomography Angiography (OCTA) and IndoCyanine Green Angiography(ICGA) helps in the visualization of the deep microvasculature of the retina and choroid, formerly mentioned technique is novel and non-invasive (Figure 2).

Figure 2: Illustrates the determination of the circumferential extent and location and of the area of the microvasculature dropout: (A) colour disc photograph, (B) infrared fundus image indicating the fovea-disc axis (blue line), (C)OCTA image of the choroidal layer, showing MVD as “focal sectoral complete loss of microvessels and was associated with the complete absence of ICG fluorescence” (D) indocyanine green angiography (ICGA) images the retinal arteriovenous (at 20 seconds after dye injection), (E) peak (at 51 seconds), and (F) late (at 3 minutes 23 seconds) phases in a glaucomatous eye with a choroidal microvasculature dropout (MvD). C-3, E-3, Magnified views of (C) and (E), respectively, revealing that the vascular dropout shown by choroidal OCTA and ICGA are nearly identical. A, C-F, dashed lines indicate the optic disc margin. Arrows indicate vascular impairments in (C) choroidal OCTA (MvD) and (D-F) ICGA (ICG “Perfusion Defect (PD)”). α Is the angular extent of the (C-1) MvD and (E-1) ICGPD, and β is the location of the (C-2) MvD and (E-2) ICGPD relative to the fovea-disc axis. Areas demarcated by the red dashed line indicate the area of the (E-3) MvD and (E-3) ICGPD. [Figure courtesy: Lee et al,2017]

Importance of angular circumference of MVD and its impact on Visual field defect:

Initial Parafoveal Visual Field Defect (IPVFD) has been of particular interest, as it has a greater impact on health and vision-related quality of life, due to its proximity with the fixation. IPVFD is associated with migraine, lower mean arterial pressure.⁽⁶⁾ The glaucomatous eyes were found to be present with IPVFD in 96% of patients with Choroidal MVD (CMVD) than in patients without MVD. In patients with a similar level of glaucoma severity, the degree of mean sensitivity(MS) loss in parafoveal areas, especially in the superior quadrant was worse in eyes with CMVD than in eyes without, in the early stage of glaucoma. Contrarily, in patients without CMVD, visual field (VF) MS was lower in the peripheral VF compared to the peripheral MS in patients with CMVD. It suggests that in eyes having CMVD, defect tends to commence from the parafoveal region, which later enlarges and extends into the peripheral VF in advanced stages. Among other vascular factors, MVD was found to be a crucial predictor for IPVFD. The location of MVD is most commonly noted in the 7’o clock position, justifying the theory of macular vulnerable zone by Hood et al.⁽⁷⁾

Figure 3: Illustrates the OCTA images of choroidal layer without choroidal MVD demarcation (top row) assessed on the en face, and with Choroidal MVD demarcation (middle low), and corresponding VF test results (bottom low) for 4 glaucomatous eyes with different Choroidal MVD angular circumferences. Areas demarcated by the red colour indicate the areas of the Choroidal MVD. Yellow lines indicate the lines connecting the disc centre to the circumferential margins of Choroidal MVD. Angle α is the “angular circumference (°)” of the Choroidal MVD in each eye. The circumferences of Choroidal MVDs in 4 eyes are 29˚, 38˚, 41˚, and 99˚, respectively. Global mean deviation (MD) values are -1.61 dB, -3.36 dB, -5.09 dB, and -8.81 dB, respectively. [Figure courtesy: Kwon et al, 2018]

Role of MVD in glaucoma progression:

The progression rates of central-most 12 points are very crucial. The progression rate in the central and peripheral regions in patients with and without CMVD is depicted in figure 4. It is evident that faster progression rates were observed in patients with CMVD. These findings help clinicians to have clarity on the relationship between the presence of MVD and IPVFD, as well as provide important insights into the clinical implications of MVD on glaucoma prognosis to central visual field loss in early stages of Open Angle Glaucoma (OAG). ⁽⁸⁾

Figure 4: Illustrating the rate of progression in patients with and without CMVD. [Figure courtesy: Jo et. al., 2019]

Does this micro sign cause a macro change in the clinic?

Well, the answer is yes! As it presents with the rapid functional changes, that needs a more aggressive treatment strategy in OAG patients having MVD sequence.

References:

1. Hayreh SS. Blood supply of the Optic Nerve Head. Ophthalmologica. 1996;
2. Kwon J, Shin JW, Lee J, Kook MS. Choroidal Microvasculature Dropout Is Associated With Parafoveal Visual Field Defects in Glaucoma. Am J Ophthalmol .2018;188:141–54.
3. Suh MH, Zangwill LM, Manalastas PIC, Belghith A, Yarmohammadi A, Medeiros FA, et al. Deep Retinal Layer Microvasculature Dropout Detected by the Optical Coherence Tomography Angiography in Glaucoma. Ophthalmology. 2016;123(12):2509–18.
4. Lee EJ, Lee KM, Lee SH, Kim TW. Parapapillary Choroidal Microvasculature Dropout in Glaucoma: A Comparison between Optical Coherence Tomography Angiography and Indocyanine Green Angiography. Ophthalmology 2017;124(8):1209–17.
5. Song MK, Shin JW, Lee JY, Hong JW, Kook MS. Choroidal microvasculature dropout is spatially associated with optic nerve head microvasculature loss in open-angle glaucoma. Sci Rep.2021;11(1):1–9.
6. Lee EJ, Kim TW, Kim JA, Kim JA. Central Visual Field Damage and Parapapillary Choroidal Microvasculature Dropout in Primary Open-Angle Glaucoma. Ophthalmology 2018;125(4):588–96.
7. Hood, Donald C, matthew Nguyen, Alyssa C Ehrlich, Ali S Raza, Leva Sliesoraityte, Carlos G. De Moraes, Robert Ritch US. A test of a model of glaucomatous damage of the macula with high density perimetry: Implications for the locations of visual field test points. Transl Vis Sci Technol. 2014;5(5):5–5.
8. Jo YH, Kwon J, Jeong D, Shon K, Kook MS. Rapid Central Visual Field Progression Rate in Eyes with Open-Angle Glaucoma and Choroidal Microvasculature Dropout. SciRep.2019;9(1):1–11.