A 47 year old man sustained a head injury after tripping over and hitting his head against a pillar. He developed a small swelling at the site of injury on his forehead just above the lateral end of the right eyebrow. He was seen in the accident and emergency (A&E) department the next morning because of pain and swelling at the site of injury. He did not have any sign of intracranial injury and the head radiographs did not show any fractures, thus the injury was classified as non-serious. However, during examination the A&E doctor noted bilaterally blurred optic discs on ophthalmoscopy. A case of papillo-oedema secondary to raised intracranial pressure (ICP) was suspected, and an urgent brain computed tomography (CT) scan was advised to rule out any intracranial pathology. An urgent ophthalmic consultation was also requested.

Examination by the ophthalmologist revealed corrected visual acuity in both eyes to be 6/6 (using Snellen’s visual acuity chart). Both pupils were equal and reacting to light, and no relative afferent pupillary defect was noted. Anterior segment examination showed slight conjunctival injection in both eyes. In both eyes, the corneas, anterior chambers, and lenses were normal. Fundoscopic examination showed discs with clear but slightly crenated margins and obliteration of the physiological optic disc cupping. Venous pulsations were present in both eyes. Retinal vasculature showed premature branching on emerging from the discs (fig 1A, B). Visual field examination by confrontation showed grossly restricted peripheral visual fields in both eyes. A diagnosis of bilateral optic nerve head drusen (ONHD) was made, which was subsequently confirmed by autofluorescence (fig 2A, B) and a B scan ultrasound (fig 3), in the ophthalmic outpatient department. Addtionally, a formal visual field examination using a Humphries visual field analyser was performed, which confirmed severe restriction of visual fields in both eyes (fig 4A, B). In the absence of any other signs of raised ICP, the CT brain scan was cancelled. The patient was advised subsequently not to drive, and the Driver and Vehicle Licensing Agency was informed. He was also advised to inform his siblings of his condition so that they could have an ophthalmic examination to exclude optic disc drusens.

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Figure 1

 Drusen disc: (A) right eye; (B) left eye.

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Figure 2

 Autofluorescence: (A) right eye; (B) left eye.

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Figure 3

 Ultrasound showing increased signal at the drusen disc.

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Figure 4

 Visual field, showing generalised constriction, right eye.

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Figure 5

 Visual field, showing generalised constriction, left eye.

DISCUSSION

ONHDs are yellow opalescent hyaline excrescences derived from calcified axonal debris present on the surface of the disc or buried in it. They are present in 0.3% of the population and are bilateral in about 75% of cases. They can be sporadic, congenital, or inherited as an autosomal dominant trait with incomplete penetrance. In early age, they remain deeply embedded deep in the nerve (but anterior to the lamina cribrosa) and not visible by ophthalmoscopy. With increasing age, they become more visible and recognisable as they come onto the surface, by the third or fourth decade of life. The optic nerve head in these cases is typically small and full, mimicking papillo-oedema. Drusens are recognised on the disc as a small, mulberry-like mass or a waxy elevation composed of a conglomerate of smaller masses. In doubtful cases if diagnosis needs to be confirmed, a simple ultrasound, autofluorescence using red free light (when viewing through a fundus camera), or a fundus fluorescin angiography (FFA) is diagnostic. In cases of children with anomalously elevated discs without visible drusen, examination of family members is essential if the distinction between true papillo-oedema and pseudo-papillo-oedema in the child is in doubt.^1–3

Three patterns of visual defect may be found: (a) enlargement of the blind spot (60% of cases); (b) arcuate or nerve fibre bundle defects producing sector cuts, ring scotomas and paracentral scotomas; or (c) generalised irregular field constrictions (as in this patient).² Visual fields are an important method of documenting and monitoring optic nerve compromise secondary to ONHD, but they are neither uniform nor diagnostic.

Ultrasonography is probably the best ancillary test to perform in adults with ONHD, demonstrating calcification within the disc. It should be performed on all adult patients presenting with elevated optic discs that are not definitively identifiable. However, it must be kept in mind that optic disc drusen are generally not calcified in children and adolescents. Hence, ultrasonography is not very helpful in diagnosing these cases.

Retinal vasculature in patients with optic disc drusen may show increased tortuosity and premature branching. Optic disc drusens may also cause spontaneous haemorrhage, which may appear peripapillary flame shaped, either intravitreal or subretinal. Incidence of retinal haemorrhage in optic disc drusen is 2–10%. It may also give rise to complications such as ischaemic optic neuropathy or choroidal neovascularisation, which cause significant visual loss.^2–4

The majority of cases of disc drusens are harmless and remain asymptomatic. As a rule, central vision is intact.

Autofluorescence is an important property of ONHD. It is best demonstrated by visualising through fluorescein angiography filters (prior to the injection of fluorescein). Using FFA, the drusens become stained during the late stages of the angiogram. In ONHD, disc is typically “normal” pink to pinkish yellow in colour, rather than waxy pale or hyperaemic. In addition, a spontaneous venous pulsation is present in about 80% of patients with ONHD, but is absent in cases of true disc oedema. Most importantly, while the disc margins may be irregular in ONHD, they are rarely blurred or obscured.

The development of papillo-oedema after head injury is caused by elevated ICP, but it is very important to realise that it takes time (3 days to 3 weeks) for papillo-oedema to develop even after raised ICP is documented. In one study, papillo-oedema was seen in only 3.5% of 426 patients with severe trauma in whom the frequency of elevated ICP exceeded 50%.⁵ Therefore, although papillo-oedema is a positive sign of elevated ICP, more importance should be given to other specific signs of elevated ICP.