From the 2nd Department of Ophthalmology (IE, VG, PN, GT), Henry Dunant Hospital, Athens; and the 2nd Department of Ophthalmology (AR, PT), University of Athens, Attiko Hospital, Chaidari, Greece.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to George Theodossiadis, MD, 13, Likiou Street, 10674 Athens, Greece. E-mail: theodossiadisg@ath.forthnet.gr
Introduction
Cone-rod dystrophy is a variant of retinitis pigmentosa in which the cone system is more severely affected compared to the rod system. Initially, the most common fundus finding in cone-rod dystrophy is retinal pigment epithelium (RPE) atrophy that often progresses to a bull’s eye pattern in the macula. Temporal disc pallor has also been observed in certain patients. Later, narrowing of the retinal vessels and peripheral extension of RPE atrophy with or without bone spicule formation can appear.1
The electroretinogram (ERG) findings are crucial for the diagnosis of cone-rod dystrophy, initially showing loss or marked decrease of cone responses while the rod responses are mildly affected. Later, in the course of the disease, the rod responses also become diminished.2 Optical coherence tomography (OCT) has shown thinning of the neurosensory retina and disorganization of the outer retinal layers.3
We are presenting a case of cone-rod dystrophy with neurosensory detachment of the macula, disintegration and focal absence of the inner segment/outer segment (IS/OS) junction layer, and intraretinal cystoid spaces in both eyes that became evident only after OCT examination.
Case Report
A 25-year-old man who complained of progressive deterioration of his vision in both eyes was examined in our clinic. His visual acuity was 0.1 bilaterally. On biomicroscopy, the anterior segments of both eyes were normal. Funduscopy revealed a zone of depigmentation around the foveola creating a bull’s eye pattern in the right and left eye and temporal pallor of the optic discs (Figs. 1A and 2A). There was no clinical evidence of cystoid maculopathy or bone spicule formation. In the macular area, fluorescein angiography showed window-defect type of hyperfluorescence without evidence of active leakage of dye or flower-petal formation. Hyperfluorescent spots were also present around the macula and along the vascular arcades due to RPE disturbances (Figs. 1B and 2B).
In the right eye, OCT depicted a neurosensory detachment in the fovea that was accompanied nasally by small cystoid spaces located in the middle layers of the retina. The macular detachment had a diameter of 1,984 μm and a height of 107 μm. There was also disruption and a complete absence of the IS/OS junction layer in some areas in the macula. The underlying RPE–choriocapillaries layer seemed to be unaffected.
In the left eye, the fovea was mainly characterized by the presence of a shallow neurosensory detachment, large cystoid spaces, and total absence of the IS/OS junction layer. There was also diffuse retinal edema in the surrounding retina. The cystoid maculopathy was more prominent in the left eye, but the height of the neurosensory detachment of the retina was larger in the right eye (Figs. 1C and 2C).
There was marked decrease of the amplitude on both the photopic and scotopic ERG (Figs. 1D and 2D). Electro-oculogram (EOG) recording was also decreased. The color vision of the patient was severely affected when tested with Ishihara’s plates. Based on the ERG results and the fundus findings, we determined that the patient had cone-rod dystrophy.
Discussion
There is great variation in the degree of dysfunction of the rod and the cone systems within both the retinitis pigmentosa and the cone dystrophy entities. In cases of retinitis pigmentosa, the gradual change of the amplitude of the responses of both the scotopic and the photopic ERG and the relationship between them makes the role of electrophysiology important in distinguishing these entities. However, because the photopic and scotopic amplitudes were both affected in our case, the diagnosis of cone-rod dystrophy was mainly based on the fundus findings. The characteristic bull’s eye appearance bilaterally in association with the absence of bone spicules or retinal vessel attenuation and the optic disc appearance render the diagnosis of retinitis pigmentosa less probable.
OCT findings in cone-rod dystrophy in a limited number of patients have shown thinning of the retina, blunting of the foveal pit, and disorganization of the outer retinal layers.3 OCT of our patient depicted the presence of new findings in both eyes: neurosensory macular detachment in association with complete absence of the IS/OS junction layer in some areas, which is in agreement with the histopathological loss of the photoreceptors cells, and cystoid macular edema.
The etiology of retinal detachment and cysts in our case is not clear. However, because cone-rod dystrophy is considered a variant of retinitis pigmentosa, the macular edema could be related to a dysfunction of the outer blood–retinal barrier4 or to an inflammatory, autoimmune process,5 as in retinitis pigmentosa.
To our knowledge, the complete absence in some areas of the IS/OS junction layer and the existence of neurosensory detachment in both eyes are new findings that became evident by OCT.
References
- Gass D. Stereoscopic Atlas of Macular Diseases, 4th ed. St. Louis, MO: Mosby; 1997:370.
- Rabb M, Tso M, Fishman G. Cone-rod dystrophy: a clinical and histopathologic report. Ophthalmology. 1986;93:1443–1451.
- Cruz-Vilegas V, Rosenfeld P, Puliafito C. Retinal dystrophies. In: Schuman J, Puliafito C, Fujimoto J, eds. Optical Coherence Tomography of Ocular Diseases, 2nd ed. Thorofare, NJ: SLACK Incorporated; 2004:413.
- Newsome DA. Retinal fluorescein leakage in retinitis pigmentosa. Am J Ophthalmol. 1986;101:354–360.
- Heckenlively JR, Jordan BL, Aptsiauri N. Association of antiretinal antibodies and cystoid macular oedema in patients with retinitis pigmentosa. Am J Ophthalmol. 1999;127:565–573. doi:10.1016/S0002-9394(98)00446-2 [CrossRef]