Page 85 - Read Online

Ma et al. J Transl Genet Genom 2022;6:179-203 https://dx.doi.org/10.20517/jtgg.2021.48 Page 183

In patients with pre-existing mCNV, the incidence of mCNV will increase in the fellow eye, with a rate of
[29]
34.8% in patients with pre-existing mCNV and 6.1% in patients without pre-existing mCNV . Myopic
[30]
CNV can occur in any degree of myopia . It is estimated that CNV develops in 3.7% and 20% of myopic
[29]
patients with diffuse chorioretinal atrophy and patchy atrophy, respectively . The final visual outcome is
unfavorable even after the application of therapy in most cases .
[31]
There are three phases of the natural course of mCNV: the active phase, the scar phase, and the atrophic
phase . The active phase is determined by the presence of hemorrhage and serous retinal detachment. The
[17]
scar phase, also called Fuchs’ spot, is a dry lesion with a grayish-white scar appearance and sometimes
pigmented. When the mCNV progresses into the atrophic phase, the CNV lesion flattens, and chorioretinal
[32]
atrophy develops around the CNV .

Myopic CNV is mostly located at the fovea , but it is occasionally located next to the myopic conus .
[34]
[33]
Different from other types of CNV, mCNV is usually small in size and accompanied by little subretinal
[35]
fluid . Bleeding from mCNV can be absorbed spontaneously in a range of 1-15 months [26,36] . Most of the
mCNV remains stable or regressed . Rebleeding occurs in 22% in ten-year follow-up .
[36]
[26]
Risk factors of myopic choroidal neovascularization
The factors associated with the visual outcome of mCNV are the age of onset, follow-up duration, CNV
location, and CNV lesion size. Yoshida et al. found that patients ≤ 40 years old at the onset of mCNV had
[33]
a better visual prognosis than those > 40 years old three years after diagnosis. Kojima et al. pointed out
[37]
that the aging RPE cells might lead to less restriction on CNV growth, and then the incompetent RPE cells
led to delayed regression of CNV and development of chorioretinal atrophy around the CNV. The visual
outcome also depends on follow-up periods. In another study, Yoshida et al. investigated the influence of
[26]
older age. In this study, a group of mCNV patients with a mean age of 46.9 years old were followed up for
more than ten years. In the first three years, more than half of them maintained the same visual acuity as the
initial value (≥ 20/200). In the tenth year, the visual acuity of 96.3% of patients dropped to < 20/200.
Meanwhile, Yoshida et al. found chorioretinal atrophy developed in the majority of the eyes after 5-10
[26]
years. Therefore, they postulated that the development of CNV-related macular atrophy was responsible for
visual loss. On the contrary, patients with younger age and smaller CNV located in the juxtafoveal region
had a favorable visual acuity better than 20/40 in a 5-year follow-up [32,38] .

Pathogenesis of myopic choroidal neovascularization
The precise pathogenesis of mCNV is still unclear. Mechanical stress, hemodynamic changes, inflammatory
factor, and genetic factor have been postulated.

Progressive thinning of the sclera and ectasia of the posterior sclera are the features of pathologic myopia.
Similar to the sclera, the choroid becomes thinner during the progression of myopia. The thinning of
choroid results from the loss of choriocapillaris and stroma and a reduction in the number of large
choroidal vessels . Mechanical stretching of the sclera plays a role in the development of mCNV . In
[39]
[40]
patients with pathologic myopia, the atrophic choroid and sclera make it easy to visualize retrobulbar
structures by swept-source optical coherence tomography (SS-OCT) or enhanced depth imaging optical
coherence tomography (EDI-OCT). Scleral perforating vessels are linear uniform hyporeflective structures
running through the sclera . The choroid circulation receives blood supply from short posterior ciliary
[41]
arteries (SPCAs). Scleral perforating vessels are originated from SPCAs, which penetrate the sclera in the
peripapillary and macular regions [42,43] . The scleral perforating vessels were detected at the site of CNV and
lacquer cracks in 70%-80% of mCNV patients [44-46] . The perforating vessels induce weakness of the local