Central retinal venous pulsations

Diagnosing raised intracranial pressure through ophthalmoscopic examination

The ophthalmoscope is one of the most useful and underutilised tools and it rewards the practitioner with a wealth of clinical information. Through illumination and a number of lenses for magnification, the direct ophthalmoscope allows the physician to visualise the interior of the eye. Ophthalmoscopic examination is an essential component of the evaluation of patients with a range of medical conditions, including diabetes mellitus, systemic hypertension and conditions associated with raised intracranial pressure (ICP). The fundus has exceptional clinical significance because it is the only location where blood vessels can be directly observed as part of a physical examination.

Optic disc swelling and central retinal venous pulsations are useful signs in cases where raised ICP is suspected. Both signs can be obtained rapidly by clinicians who know how to recognise them. Although optic disc swelling supports the diagnosis of raised ICP, the presence of central retinal venous pulsations may indicate the contrary.

In the standard technique for direct ophthalmoscopy, the patient is positioned in a seated posture and asked to fix their gaze on a stationary point directly ahead. Pupillary dilation, removal of the patient’s spectacles and dim room illumination usually aid the examination. To start examining the patient, set the ophthalmoscope dioptres to zero — alternatively, a suitable setting would be the sum of the refractive errors of the patient and the examiner. Use the right eye to examine the patient’s right eye and vice versa. Using a slight temporal approach facilitates the identification of the optic disc, which also minimises awkward direct facial contact with the patient. Examine the red reflex at just under arm’s length. A pale or absent red reflex may suggest media opacity, such as a cataract. Next, on approaching the patient and obtaining a clear view of a retinal vessel, follow its course toward the optic disc. The presence or absence of venous pulsations should be appreciable (see the video at www.mja.com.au; pulsations of the central vein are clearly visible at the inferior margin of the optic disc). These pulsations, usually of the proximal portion of the central retinal vein, are most readily identified at the optic disc. The examination of the fundus should be concluded by visualisation of the four quadrants of the retina and examination of the macula.

Central retinal venous pulsations are traditionally attributed to fluctuations in intraocular pressure with systole, although this is may be an incomplete explanation.1 Patients with central retinal venous pulsations generally have cerebrospinal fluid pressures below 190 mmHg.2 Based on the results of Wong and White,3 the positive predictive value for retinal venous pulsations predicting normal ICP was 0.88 (0.87–0.9) and the negative predictive value was 0.17 (0.05–0.4).

This is important when considering lumbar puncture and when neuroimaging is not available. A limitation of this sign is that about 10% of the normal population4 do not have central retinal venous pulsations visible on direct ophthalmoscopy.4 The absence of central retinal venous pulsations does not, by itself, represent evidence of raised ICP; some patients with elevated ICP may still have visible retinal venous pulsations.

Papilloedema (optic disc swelling caused by increased ICP) may develop after the loss of retinal venous pulsations. This change in the appearance of the optic disc and its surrounding structures may be due to the transfer of elevated intracranial pressure to the optic nerve sheath. This interferes with normal axonal function causing oedema and leakage of fluid into the surrounding tissues. Progressive changes include the presence of splinter haemorrhages at the optic disc, elevation of the disc with loss of cupping, blurring of the disc margins, and haemorrhage. In later stages, there is progressive pallor of the disc due to axonal loss. A staging scale, such as that of Frisén,5 can be used to reliably identify the extent of papilloedema (Box).

Box – Stage 4–5 papilloedema (5) showing disc and nerve fibre swelling, haemorrhage, loss of the optic cup and obscuration of the vessels at the disc margin

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Source: Bruce AS, O’Day J, McKay D, Swann PG. Posterior eye disease and glaucoma A–Z. London: Elsevier Health Sciences, 2008.