Torpedo maculopathy is a rare, benign, and congenital maculopathy, which is usually
asymptomatic, but occasionally found during routine examination. It often occurs in
patients without any relevant medical history and is most commonly unilateral, although
bilateral cases have been reported previously[4]. The torpedo maculopathy appears
as a transverse oval, yellowish-white hypo-pigmented lesion, and is located in the
temporal macular area, with a tip pointing towards the central fovea.
Till now, the etiology of this disease is still unclear. Few studies have been reported
to explain the pathogenesis of the lesion. Pian et al[5] assumed that it might be
a developmental defect within the nerve-fiber layer at the horizontal raphe. Shields[6]
suggested a persistent defect in the development of RPE during the fetal temporal
bulge, which might be the reason for the cause of the lesion. Golchet et al[7] hypothesized
that the lesion may be related to dysmorphia of the emissary canal of the long posterior
ciliary artery and nerve.
Microperimetry precisely revealed the correlation of retinal sensitivity and fundus
lesion, and also detected microscotoma within the central visual field that may not
be detectable by using standard perimetry methods[8]. Published reports have demonstrated
that scotoma is frequently associated with torpedo lesion[9-11]. Focal RPE atrophy
results showed that reduced metabolites and oxygen supply for the inner retina, secondary
choriocapillaris loss and photoreceptor degeneration are associated with the reduction
of retinal sensitivity[12]. This case was different from the earlier reports, and
there was no microscotoma seen, the retinal sensitivity appeared normal, and the patient
had good visual function. Therefore, we speculated that the degree of RPE atrophy
was mild in this case, and does not harm the function of overlying photoreceptors.
Using SD-OCT, the outer retina was disorganized, and showed significant atrophy of
RPE with an intact ellipsoid zone in this case. We thought that the RPE still preserved
the function of ingesting photoreceptor cell outer segment, so the ellipsoid zone
still remained intact and the patient has preserved the normal visual function. Evan
et al[13] identified two patterns of abnormalities: type 1, attenuation of outer retinal
structures without outer retinal cavitation; and type 2, those with both attenuation
of outer retinal structures and outer retinal cavitation. According to their theory,
this patient was included under type 1 torpedo maculopathy. Besides, they also observed
that the patients with type 1 lesion (age, 4–37) tended to be younger than those with
type 2 lesion (age, 13–73) [13]. This patient was aged 30, and was consistent with
the characteristics summarized by them.
OCTA non-invasively detects the movement of red blood cells to reveal the retinal
and choroidal vascular system. Therefore, alterations in the choriocapillaris can
be visualized by using OCTA. Papastefanou and his colleagues[14] described the OCTA
features of torpedo lesions with OCTA, and revealed choroidal vascular segmentation
with hypo-reflectivity (atrophy), which in turn was correlated to the OCT of the subretinal
cleft. While there was no subretinal cleft in our patient, and the OCTA findings were
different. OCTA choroid capillary segment revealed increased density of choroidal
vasculature, revealing thinner RPE as the optical signal transmission for the increased
choroidal thickness; however, the superficial and deep layers were normal. Comparison of our case with the previous reported cases[14] revealed that our case
had an early stage according to the OCT classification.
Autofluorescence signal is predominantly derived from lipofuscin within the RPE[15].
In our case, FAF showed normal signals mostly with slight hyperautofluorescence at the nasal lesion.
The possible explanation for this was due to attenuation of both RPE and outer nuclear
layer.
FFA of the lesion showed variegated fluorescence and no leakage and change in the
morphology during the whole imaging process. This demonstrated no choroidal neovascularization
(CNV), while few cases showed the existence of CNV[16]. Lesions in our case were still
limited to RPE without CNV.
Differential diagnosis such as posterior uveitis should be carefully addressed. Posterior
uveitis is also known as choroiditis, and is characterized by vitreous exudation and
choroidal vasodilatation, resulting in CNV and visual reduction. Examinations showed
by OCTA, FFA and FAF in posterior uveitis are distinguished from torpedo maculopathy.
Early hypo-fluorescence followed by late leakage on FFA was observed in active choroiditis
lesions. However, healed lesions represented hypo-fluorescence during the early phase
with staining but no leakage in the late phase. According to FAF, ill-defined hyper-autofluorescence
was observed in active choroiditis lesions, while rounded edges and hypo-autofluorescence within the lesion were shown
in healed choroiditis[17]. These are quite different from the torpedo maculopathy.
However, there are several limitations in this study. The sample size of the study
was small, and indocyanine green angiography was not performed, which helps in better
understanding of the differential diagnosis of this disease. Besides, no further follow-up
examination is a conceivable limitation of this study.
In conclusion, a case of torpedo maculopathy by using fundal photographs, IR, microperimetry
visual field, OCT, OCTA, FAF, and FFA simultaneously has been presented for the first
time. It is in a very early stage or a mild type of torpedo maculopathy. The natural
development of torpedo maculopathy is still unclear, whether it does not develop or
develops very slowly. Multimodal imaging provides precious and detailed information
for easily diagnosing and deeply understanding this rare disease. This disease is
very rare, and needs more case reports worldwide and longer follow-up time to further
understand the etiology, characteristics and development of this lesion.