Introduction
Posterior polar central choroidal dystrophy is a form of choroidal dystrophy characterized by loss of retinal pigment epithelium (RPE) and choriocapillaris. Involvement occurs in the posterior fundus within the vascular arcades and sometimes surrounding the optic nerve. This term was first used by Yannuzzi1 and since then there have been no further reports of this rare condition. In this case report, we present the results of fluorescein angiography, fundus autofluorescence (FAF) imaging, optical coherence tomography (OCT) and electrophysiological testing in this rare disease.
Discussion
Primary choroidal dystrophies which affect the central macula are referred to as central areolar choroidal dystrophy, posterior polar central choroidal dystrophy, posterior polar annular dystrophy, posterior polar hemispheric dystrophy, and central and peripheral annular choroidal dystrophy.1 All forms of these choroidal dystrophies feature varying patterns of atrophy involving both the RPE and choriocapillaris. In posterior polar central choroidal dystrophy, the atrophic abnormality involves the posterior fundus within the vascular arcades and sometimes the area surrounding the optic nerve.1
OCT, which provides detailed analysis of retinal architecture, revealed atrophy of the choriocapillaris and outer retinal layers, and FAF images helped to localize the boundaries of the atrophic area.
The differential diagnosis of this condition included central areolar choroidal dystrophy, geographic atrophy, and pathologic myopia. We excluded pathologic myopia because the patient had refractive error less than -6.0 D. In central areolar choroidal dystrophy, atrophy of the RPE and choriocapillaris occurs in the foveal region and does not spread through the vascular arcade. The results of an electrophysiological study in a patient with central areolar choroidal dystrophy have been reported in the literature. Ponjavic et al.2 reported the result of full-field electroretinography in this disorder. They showed that the cone b-wave amplitude in ERG is decreased and the cone b-wave implicit time is prolonged. This result shows that although it is a choroidal disease, it also affects most or all of the retinal cones. Lotery et al.3 reported that pattern VEP and pattern ERG are the most sensitive electrophysiological tests which show abnormality in clinically normal but genetically affected central areolar choroidal dystrophy patients. Eventually in later disease stages, atrophy results in abnormal cone and rod responses on full-field ERG due to widespread photoreceptor dysfunction.
In another case report, full-field and multifocal ERG results of a patient with central areolar choroidal dystrophy showed normal photopic and scotopic responses in the full-field ERG and severely depressed retinal function of the perifoveal macula corresponding to the atrophic area in the multifocal ERG.4
Posterior polar central choroidal dystrophy affects a larger area than central areolar choroidal dystrophy and in our case the patient was in the advanced stage. Therefore, the patient demonstrated abnormal photopic and scotopic responses in full-field ERG as well as pattern VEP and pattern ERG. At the same time, all waves showed reduced amplitude in multifocal ERG.
Another disease in the differential diagnosis may be geographic atrophy, which is a devastating complication of age-related macular degeneration. Geographic atrophy of the RPE may be classified as drusen-related or neovascularization-related.5 Because there were no drusen or fibrovascular tissue in either eye and the findings were symmetrical, this diagnosis was excluded.
Based on all of these findings, we diagnosed the patient with posterior polar central choroidal dystrophy. We share the results of fluorescein angiography, FAF imaging, OCT, and electrophysiological tests in our case in order to remind clinicians of this rare disease.
