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 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 pointed towards the central fovea.
Till now, the etiology of the 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 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 can precisely reveal the correlation of retinal sensitivity and fundus lesion, and also detect microscotoma within the central visual field that may not be detectable using standard perimetry methods[8]. Published reports 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 very light in this case, and does not harm the function of overlying photoreceptors.
Using SD-OCT, the outer retina was disorganized, and significant atrophy of RPE with an intact ellipsoid zone was seen in this case. We thought that RPR still preserved the function of ingesting photoreceptor cell outer segment, so the ellipsoid zone still remained intact and the patient preserved the normal visual function. Evan et al[13] identified two patterns of abnormality: 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 30, and was consistent with the characteristics summarized by them.
OCTA non-invasively detected the movement of red blood cells to reveal the retinal and choroidal vascular system. Therefore, alterations in the choriocapillaris can be visualized 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 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. Comparison of our case with the previous reported cases[14], our case could be considered as an early stage according to the OCT classification.
Autofluorescence signal is predominantly derived from lipofuscin within the RPE[15]. In our case, FAF showed slight hypoautofluorescene with marginal mild hyperautofluorescence. The possible explanation for this was that the hypoautofluorescene of thinner RPE within the lesion provides a sharp contrast to the physiological hyper-autofluorescence within the marginal region.
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.
In conclusion, we herein presented a case of torpedo maculopathy using fundal photograph, IR, microperimetry visual field, OCT, OCTA, FAF, and FFA simultaneously for the first time. We demonstrated it to be present 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 to easily diagnose and deeply understand this rare disease. This disease is very rare, and needs more case reports worldwide and longer follow-up to further understand regarding the etiology, characteristics and development of this lesion.