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Patient suspected of having either AMD or pattern dystrophy
The patient reported ‘hazy’ vision in both eyes that did not improve or worsen.
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A 52-year-old man was referred to the New England Eye Center for evaluation with the presumptive diagnosis of either age-related macular degeneration or pattern dystrophy. The patient said that he was experiencing chronic “hazy” vision, which was worse in the left eye. He denied photopsia, nyctalopia or metamorphopsia. He said that the poor vision was not progressive, and he believed that his vision was fine when he was younger. Nothing improved or worsened the vision, and the patient did not have any pain.
| Shazia Ahmed | My Hanh T. Nguyen |
The patient’s review of systems was unremarkable. His ocular history was significant for previously diagnosed amblyopia in the left eye many years ago, and the patient’s family history was significant for an unspecified blindness in his mother, who had long since passed away. The patient said that he was healthy and was not currently taking any prescription medications or eye drops. He said that he was a heavy smoker and drinker, however.
Examination
On examination, the patient’s visual acuity was 20/60 in the right eye and 20/200 in the left eye with best correction. IOP, extraocular motility and pupil examination were normal in both eyes. There was no afferent pupillary defect in either eye. Manifest refraction demonstrated no improvement in vision.
Slit lamp examination of the ocular adnexae and anterior segment was unremarkable except for mild nuclear sclerotic cataracts in both eyes. Dilated fundus examination (Figure 1) was notable for an annular area of retinal pigment epithelium loss and mottled pigmentation, as well as sharply demarcated areas of chorioretinal atrophy in the macula of both eyes. The optic discs were remarkable for bilateral prepapillary vascular loops consistent with Bergmeister’s papillae. The retinal vessels and peripheral fundi of both eyes were unremarkable.
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Images: Chaturvedi V, Rhee D, Duker JS |
What is your diagnosis?
Macular changes
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These macular findings are consistent with AMD or pattern dystrophy. Other macular dystrophies, including central areolar choroidal dystrophy and North Carolina macular dystrophy, should be entertained, especially in the setting of a possible positive family history.
In addition, due to the symmetric annular nature of the macular changes at the level of the retinal pigment epithelium, it is necessary to consider various etiologies of bull’s eye maculopathy, including cone dystrophy, medication toxicity (phenothiazines, chloroquines) or systemic conditions such as olivopontocerebellar atrophy and neuronal ceroid lipofuscinosis (Batten’s disease). The absence of systemic medications makes pharmacologic toxicity unlikely, and the late onset and absence of systemic symptoms renders Batten’s disease and olivopontocerebellar atrophy doubtful.
A fluorescein angiogram and both standard and ultrahigh resolution spectral optical coherence tomography (OCT) of the macula were performed. Fluorescein angiogram (Figure 2) showed staining of pigmentary changes and peripapillary atrophy without leakage in both eyes. Standard OCT appeared relatively normal; however, ultrahigh resolution OCT demonstrated disruption of the external limiting membrane and diffuse photoreceptor atrophy in both eyes (Figure 3).
Because of these findings, an electroretinogram (ERG) was performed on both eyes, which showed normal scotopic responses but reduced photopic (30 Hz flicker) responses (Figure 4). These findings were consistent with cone dystrophy.
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Discussion
Cone dystrophies are a heterogeneously inherited group of disorders in which cone photoreceptor function is typically normal at birth. The age of onset of symptoms can vary from the mid-teens to the seventh decade. The symptoms are most commonly manifest as day-blindness (hemeralopia), a decrease in visual acuity and color sensitivity, and photosensitivity or photophobia. Final visual acuity in these patients is rarely better than 20/200 or 20/100.
This spectrum of dystrophies can range from abnormalities with the cones only (cone dystrophies) to cone dysfunction in addition to varying degrees of rod dysfunction (cone-rod dystrophies). In either case, the cone abnormalities predominate.
Bull’s eye maculopathy is neither pathognomonic nor a sine qua non for cone dystrophies. Some cases may show no macular changes at all. Occasionally, temporal pallor of the optic disc has been noticed. Visual field testing usually shows a bilateral central scotoma.
The ERG confirms the diagnosis in these cases. Absence or a minimal response of the cones on ERG with normal scotopic responses is typical for cone dystrophies. Ladewig and colleagues in 2003 showed that both late-onset cone dystrophy and AMD can appear similar in terms of fundus findings, visual acuity, color deficits and visual fields; however, the ERG was significantly different between the two disease entities. (Interestingly, the AMD patients in this study showed a subnormal photopic [30 Hz flicker] response, but other studies have both confirmed and refuted these findings.) It is important to note that visual acuity is not a good indicator for the extent of cone dysfunction, as an abnormal photopic response on ERG may occur in patients with good visual acuity due to widespread dysfunction of the peripheral cones.
Rod monochromats can share the same ERG and fundus findings as someone with cone dystrophy; however, the onset of symptoms occurs at birth. In addition, blue-cone monochromats may exhibit similar ERGs due to the relative paucity of blue cones throughout the retina, but like rod monochromats, these patients have defective cone function since birth.
Cone and cone-rod dystrophies have been linked with mutations in the RCD, ABCA4 and guanylate cyclase genes, as well as other polymorphisms. It is possible that genetic analysis may aid in the diagnosis and counseling of affected individuals.
There are no known treatment modalities for this condition. Patients should be informed of the visual prognosis and referred to low-vision specialists when appropriate.
For more information:
- Vivek Chaturvedi, MD, David Rhee, MD, and Jay S. Duker, MD, can be reached at New England Eye Center, Tufts University School of Medicine, 750 Washington St., Box 450, Boston, MA 02111; 617-636-4219; fax: 617-636-4866; Web site: www.neec.com.
- Edited by Shazia Ahmed, MD, and My Hanh T. Nguyen, MD. Drs. Ahmed and Nguyen can be reached at New England Eye Center, Tufts University School of Medicine, 750 Washington St., Box 450, Boston, MA 02111; 617-636-4219; fax: 617-636-4866; Web site: www.neec.com. Drs. Ahmed and Nguyen have no direct financial interest in the products mentioned in this article, nor are they paid consultants for any companies mentioned.
References:
- Kurz-Levin MM, Halfyard AS, et al. Clinical variations in assessment of bull’s-eye maculopathy. Arch Ophthalmol. 2002;120(5):567-575.
- Ladewig M, Kraus H, Foerster MH, Kellner U. Cone dysfunction in patients with late-onset cone dystrophy and age-related macular degeneration. Arch Ophthalmol. 2003;121(11):1557-1561.
- Rowe SE, Trobe JD, Sieving PA. Idiopathic photoreceptor dysfunction causes unexplained visual acuity loss in later adulthood. Ophthalmology. 1990;97(12):1632-1637.
- Simunovic MP, Moore AT. The cone dystrophies. Eye. 1998;12(Pt 3b):553-565.