Optic disc pallor: a false localizing sign

Diagnostic Yield of Investigations in Symmetric Optic Neuropathy

BACKGROUND

Symmetric optic neuropathy (SON) is commonly seen in neuro-ophthalmic practice and is often discovered incidentally. Although multiple investigations might be performed to discover the underlying cause, they are not always indicated. The aim of this study was to report a clinically reasonable and cost-effective approach to investigating patients with SON.

METHODS

SON was defined as bilateral optic neuropathy with normal and/or symmetrically decreased central visual acuity, absence of relative afferent pupillary defect, presence of symmetric optic disc pallor, symmetric thinning of peripapillary retinal nerve fiber layer on optical coherence tomography, and absence of other identifiable causes of optic neuropathy. Records of all patients diagnosed with SON seen at a tertiary university-affiliated neuro-ophthalmology practice from 2016 to 2022 were reviewed to identify the yield of various investigations. Clinical data from the initial and last follow-up visit were obtained. Subgroup analysis was performed to ascertain whether diagnostic yield is higher in patients with severe visual loss (central acuity worse than 20/40) compared with those with mild visual loss (acuity 20/40 or better).

RESULTS

One hundred thirty-six patients met inclusion criteria. Testing for OPA1 and OPA2 mutations had the highest diagnostic yield (16.0%), followed by mitochondrial genome sequencing (13.6%), serum vitamin B12 (6.1%), and serum folate (1.6%). MRI brain was performed in 54.4% of patients and had a diagnostic yield of only 5%. Both patients who had abnormal MRI had symptoms of demyelination at presentation. Patients were followed for a mean of 15.0 (SD 21.3) months. The most frequently identified etiologies of SON were Leber hereditary optic neuropathy (8.1%), alcohol/tobacco amblyopia (7.4%), vitamin B12 deficiency (5.9%), and dominant optic atrophy (2.9%). Patients with severe visual impairment were more likely to have a final diagnosis compared with those with milder visual impairment (63.9% vs 12.0%, P < 0.001).

CONCLUSIONS

The diagnostic yield of investigating SON in patients with preserved visual function, normal diet, and absence of other neurological symptoms is very low. It is reasonable to observe patients with SON with mild visual impairment, reserving costly investigations for those with the visual acuity worse than 20/40 or progressive course.

Electrophysiology in neuro-ophthalmology

This chapter reviews common applications of visual electrophysiology relevant to neuro-ophthalmology practice. The use of standard tests and extended protocols are described including the cortical visual evoked potential and pattern and full-field electroretinogram (PERG; ERG) methods, the latter including the photopic negative response. Abnormalities of these recordings are rarely specific but provide valuable diagnostic guidance and an objective measure of visual pathway function, difficult or impossible to infer by other methods. The electrophysiological phenotypes associated with Leber hereditary optic neuropathy, OPA1- and SSBP1-associated dominant optic atrophy, and WFS1-related syndromes are described. Typical changes in retinal and optic nerve function tests associated with acquired disease are highlighted, including those related to demyelination, ischemic, compressive, nutritional and toxic, and nonorganic etiologies. The importance of complementary testing using different electrophysiological techniques is emphasized, for the purposes of differential diagnosis and in disorders that may masquerade as optic nerve pathology.

Detailed functional and structural characterization of a macular lesion in a rhesus macaque

PURPOSE

Animal models are powerful tools to broaden our understanding of disease mechanisms and to develop future treatment strategies. Here we present detailed structural and functional findings of a rhesus macaque suffering from a naturally occurring bilateral macular dystrophy (BMD), partial optic atrophy and corresponding reduction of central V1 signals in visual fMRI experiments when compared to data in a healthy macaque (CTRL) of similar age.

METHODS

Retinal imaging included infrared and autofluorescence recordings, fluorescein and indocyanine green angiography and spectral domain optical coherence tomography (OCT) on the Spectralis HRA + OCT platform. Electroretinography included multifocal and Ganzfeld-ERG recordings. Animals were killed and eyes analyzed by immunohistochemistry.

RESULTS

Angiography showed reduced macular vascularization with significantly larger foveal avascular zones (FAZ) in the affected animal (FAZBMD = 8.85 mm(2) vs. FAZCTRL = 0.32 mm(2)). OCT showed bilateral thinning of the macula within the FAZ (total retinal thickness, TRTBMD = 174 ± 9 µm) and partial optic nerve atrophy when compared to control (TRTCTRL = 303 ± 45 µm). Segmentation analysis revealed that inner retinal layers were primarily affected (inner retinal thickness, IRTBMD = 33 ± 9 µm vs. IRTCTRL = 143 ± 45 µm), while the outer retina essentially maintained its thickness (ORTBMD = 141 ± 7 µm vs. ORTCTRL = 160 ± 11 µm). Altered macular morphology corresponded to a preferential reduction of central signals in the multifocal electroretinography and to a specific attenuation of cone-derived responses in the Ganzfeld electroretinography, while rod function remained normal.

CONCLUSION

We provided detailed characterization of a primate macular disorder. This study aims to stimulate awareness and further investigation in primates with macular disorders eventually leading to the identification of a primate animal model and facilitating the preclinical development of therapeutic strategies.

Increasing exotropia and decreasing vision in a school-aged boy

An 8-year-old boy presented with bilateral visual loss and an increasing exotropia, and later developed deteriorating school performance. Magnetic resonance imaging of the head showed bilateral, symmetric, T2, and FLAIR white matter abnormalities in the parieto-occipital regions. Elevated serum very long chain fatty acids confirmed the diagnosis of X-linked adrenoleukodystrophy. Ophthalmologists should be aware of the diagnosis in boys with visual loss, hyperactivity, behavioral changes, and deterioration in school performance. Visual loss may be the presenting or predominant feature in X-linked adrenoleukodystrophy.

Electrophysiological assessment of optic nerve disease

The electrophysiological findings in optic nerve and primary ganglion cell dysfunction are reviewed. The value of the pattern reversal visual-evoked potential (VEP) in the diagnosis of optic nerve disease, and the pattern appearance VEP in the demonstration of the intracranial misrouting associated with albinism, are discussed. The pattern electroretinogram (PERG) is used in the direct assessment of ganglion cell function. The use of PERG or multifocal electroretinography (mfERG), to enable the distinction between VEP delay due to optic nerve disease and that due to macular dysfunction, is described.

Pattern electroretinography (PERG) and an integrated approach to visual pathway diagnosis

The pattern electroretinogram (PERG) provides an objective measure of central retinal function, and has become an important element of the author's clinical visual electrophysiological practice. The PERG contains two main components, a positivity at approximately 50ms (P50) and a larger negativity at approximately 95ms (N95). The P50 component is affected by macular dysfunction with concomitant reduction in N95. The PERG therefore complements the Ganzfeld ERG in the assessment of patients with retinal disease. In contrast, the ganglion cell origins of the N95 component allow electrophysiological evaluation of ganglion cell function both in primary disease and in dysfunction secondary to optic nerve disease, where selective loss of N95 can be observed. Both macular dysfunction and optic nerve disease can give abnormalities in the visual evoked cortical potential (VEP), and the PERG thus facilitates more meaningful VEP interpretation. This review addresses the origins and recording of the PERG, and then draws on extensive clinical data from patients with genetically determined retinal and macular dystrophies, other retinal diseases and a variety of optic nerve disorders, to present an integrated approach to diagnosis.

Coffee and doughnut maculopathy: a cause of acute central ring scotomas

AIMS

To report the clinical features of five patients with non-progressive central ring scotomas of acute onset associated with excellent retained visual acuity.

METHODS

Complete neuro-ophthalmological examinations were performed. Visual fields were performed by tangent screen, Goldmann, or Humphrey perimetry. In some cases further testing was carried out including fundus photography, fluorescein angiography, ERG, VEP, and neuroimaging.

RESULTS

The patients were three women and two men whose ages ranged from 25 to 57 years. Four patients were heavy caffeine consumers while the fifth patient experienced an episode of hypotension. Vision loss was acute in all cases. The onset of vision loss was bilateral/simultaneous in three cases, bilateral/sequential in one case, and unilateral in one case. All affected eyes retained visual acuities of 20/25 or better. Colour vision was subnormal in three of four cases. Visual field defects were characterised by a central ring scotoma having an outer diameter less than 10 degrees. Fundus examination demonstrated temporal optic nerve pallor in three patients (five of 10 affected eyes) and reddish, petaloid macular lesions in one patient. Good visual acuity was maintained for the duration of follow up in all five patients.

CONCLUSION

Central ring scotomas with excellent retained visual acuity may present as an acute, bilateral syndrome in patients who are heavy caffeine consumers. The configuration of visual field loss and its location, combined with the presence of temporal pallor in five eyes, suggest that the defect localises to the inner layers of the macula. While these cases could be considered an expansion of the clinical spectrum of acute macular neuroretinopathy, some may represent a distinct entity.