Sir, Olali et al1 presented a case of biopsy-proven giant cell arteritis (GCA) with atypical visual loss. The visual impairment had manifested as bilateral reduction of visual acuity but with sparing of peripheral field. Fluorescein angiography provided the denouement: there was focal perfusion defect localised to the submacular choroid. The angiographic curiosity was more pronounced in the right eye, with its central scotoma of greater eminence, as evidenced by a poorer acuity. The authors noted that this pattern—of isolated focal ischaemic choroidopathy in GCA patients—had been reported earlier.2 However, as the literature burgeons we become ever remiss of treasures from the past. Almost 40 years ago a monograph called ‘Segmental nature of the choroidal vasculature' appeared in the British Journal of Ophthalmology, a masterclass by SS Hayreh on the anatomy and haemodynamics of the choroidal vascular system, with allusion to the superimposition of diseases including arteritis.3 A homage to this contribution better explains the features observed by Olali et al1 in their patient. They wished specifically to report ‘pigmentary disturbance' at the maculae in a case of GCA in whom there appeared no other ophthalmoscopic features. A reference to the oeuvre of Hayreh affords insight: acute submacular choroidal ischaemia causes pallor of the overlying retinal pigment epithelium. Eventually, the pallid zone acquires depigmentation, the precise ophthalmoscopic anomaly visible in the patient under discussion. Indeed the description appended by Olali et al1 to their case report can be elevated to a formulation in dilgenter: in their presented arteritic case, the occurrence of submacular ischaemia (with sparing of the optic nerve head) denoted hypoperfusion in the lateral posterior ciliary artery (LPCA), the vascular stalk that serves the temporal posterior choroid. As perfusion pressure decreased inside the LPCA—in this situation as consequence of arteritis—the submacular choroid was the first casualty of ischaemia because it is a watershed vascular territory. This is the explanatory nub of the clinical constellation detected in this patient. Of further intrigue, the optic nerve head escaped infarction because it retained perfusion from the medial PCA and a meshwork of circumferential short PCAs. With unsuppressed disease progression, however, the inevitable course would have been arteritic anterior ischaemic optic neuropathy, as the operational nerve head feeders succumbed finally to arteritis. Through a marshalling of superb diagrams, the outstanding duo of McLeod and Hayreh,4 both now emeritus professors, have earlier expounded the behaviour of the choroidal tree as observed after piecemeal cauterisation of its various feeder PCAs. Also in this patient, the submacular choroidal ischaemia was cast into a sharp outline by the 19-s image from the angiogram. Later, at 52 s, the outermost fringe of the ischaemic zone had turned indistinct. Explanation for this observation again comes from the experiments of landmark stature, which hark back some 40 years. As ischaemic patches form within the choroid there is remedial response from neighbouring vascular systems, instanced among others by retrograde flux in the vortex veins. When such zones of choroidal ischaemia are captured over days and weeks via serial angiograms, the non-perfused zones are seen to contract in area. The speed of angiographic filling improves through brisk consolidation of collateral flow. Thus, late frames were found to show dye ingress into choroidal zones that showed stark ischaemia in the opening sequence. The broader message for ophthalmologists is that, in its incipient stealthy phase, GCA can produce localised ischaemic patches in the choroid while entirely sparing the optic nerve and retinal arterial system. Ophthalmologists must be cognizant of this possibility when faced with an older patient who has seemingly inexplicable visual loss and biomicroscopic signs of minimal intensity.
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May 31, 2023
Rafael Godoy + 3
Open Access
