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Boy referred for glaucoma suspect evaluation
The right optic nerve was pink and sharp with a 0.8 cup-to-disc ratio, and the left optic nerve had pallor with a 0.9 cup-to-disc ratio.
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A 10-year-old boy was referred to Tufts New England Eye Center for a glaucoma suspect evaluation after a routine eye exam. The patient was born full-term with no complications during pregnancy or delivery. He had a history of mild developmental delay. Medical history was otherwise negative. He was on no medications, and family history was noncontributory.
Examination
The patient’s best corrected visual acuity was 20/25 in the right eye and 20/50 in the left eye. Pupils were equal, round and reactive with no relative afferent defect. His ocular motility was full, and he was orthophoric in all gaze positions. He saw 10 of 10 Ishihara color plates with each eye. He had 60 arc seconds of stereoacuity. IOP was 14 mm Hg in the right eye and 12 mm Hg in the left eye. Central corneal thickness was 473 µm in the right eye and 484 µm in the left eye. Cycloplegic refraction was –1.25 sphere in the right eye and –2.75 +1.25 × 090 in the left eye.
Source: Lauren Bierman, MD, Sylvia H. Yoo, MD, and Thomas R. Hedges III, MD
On slit lamp examination, the conjunctivae in both eyes were white and quiet, the corneas were clear, and the anterior chambers were deep and quiet bilaterally. The irides were round and reactive, and the lenses were clear. On dilated fundus exam, the right optic nerve was pink and sharp with a 0.8 cup-to-disc ratio, and the left optic nerve had pallor with a 0.9 cup-to-disc ratio (Figure 1). Humphrey visual field 24-2 demonstrated superior and inferior arcuate changes with a nasal step in the right eye. In the left eye, there was a superior and inferior nasal step with a superior arcuate defect approaching fixation (Figure 2). Ganglion cell analysis showed thinning nasally in the right eye and temporally in the left eye, consistent with a predominant right homonymous hemianopia seen on visual field testing (Figure 3).
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Glaucoma suspect evaluation
The differential diagnosis includes juvenile glaucoma, optic neuropathy due to compression, ischemia, toxic/nutritional abnormalities, congenital anomalous optic nerves or an occipital lobe lesion. Additional testing was ordered, including MRI of the brain and orbits with and without contrast. Lab work included a complete blood count, vitamin B12 and folate levels, and a heavy metal panel. The MRI was initially reported as unremarkable without evidence of infarction, hemorrhage or space-occupying lesion. However, on further review of the MRI, an area of encephalomalacia was noted involving the occipital lobe bilaterally, more extensive on the left than right side and centered at the superior aspect of the calcarine fissure. In addition, there was thinning of the cortex with atrophy of the underlying white matter (Figure 4).
Discussion
When evaluating a new patient referred as a glaucoma suspect, it is important to recall the patterns that are typically seen in glaucomatous optic neuropathy vs. non-glaucomatous optic neuropathy. Glaucomatous nerves usually do not have rim pallor, and there is often verticalization of the optic nerve cup with nasalization of the vessels. In addition, vision is usually unaffected until advanced stages, and the visual field often correlates with the appearance of the disc. Our patient had nerve pallor, especially in the left eye with a large cup-to-disc ratio without significant verticalization. IOPs were normal, although the corneal thicknesses were notably thin. Further evaluation for the etiology of his exam findings was thus pursued. The abnormalities seen in his occipital lobe better explain his exam findings. He appears to have a likely congenital postsynaptic abnormality of the visual pathways leading to transsynaptic ganglion cell and nerve fiber layer loss and optic atrophy of both eyes with a predominant right homonymous hemianopia.
Large cup-to-disc ratio in normal-sized optic discs is a unique form of optic nerve hypoplasia also seen in patients with a history of periventricular leukomalacia. In these patients, hypoxic-ischemic injury to the optic radiations likely results in transsynaptic degeneration of the optic axons. This is most commonly seen in patients born prematurely with a history of intraventricular hemorrhage in the neonatal period. This patient had a normal birth history per his family.
When following pediatric patients with a homonymous hemianopia, it is important to monitor for the development of strabismus, as an adaptive strabismus can develop. In pediatric patients with a homonymous hemianopia, there is a 24% prevalence of exotropia and 9% prevalence of esotropia, which is higher than the general population at 1.5% and 5%, respectively. The eye with strabismus typically drifts toward the visual field defect, likely as a way to increase the binocular horizontal visual field. Therefore, it is important to recognize this adaptation when considering intervention for the strabismus.
Clinical course continued
The patient will be monitored every 6 months with OCT and was registered with the Massachusetts Commission for the Blind. He has developed an intermittent exotropia, which will be monitored as well.
- References:
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- For more information:
- Lauren Bierman, MD, Sylvia H. Yoo, MD, and Thomas R. Hedges III, MD, can be reached at New England Eye Center, Tufts University School of Medicine. 800 Washington Street, Box 450, Boston, MA 02111; website: www.neec.com.
- Edited by Adam T. Chin, MD, and Omar Dajani, MD. They can be reached at the New England Eye Center, Tufts University School of Medicine, 800 Washington St., Box 450, Boston, MA 02111; website: www.neec.com.