In-vivo high resolution imaging of optic nerve head drusen using spectral-domain Optical Coherence Tomography

This is a retrospective case series of 5 patients with bilateral ONHD with a best-corrected visual acuity of 20/20 and no other posterior segment pathology. All the patients underwent fundus photography, fundus autofluorescence, B-scan ultrasonography, Spectralis OCT and Humphrey 30-2 threshold visual fields.All 5 patients had surface ONHD which were autofluorescent and echodense on B-scan ultrasonography. Spectralis OCT findings in the corresponding areas include 'scattered spots with high reflectivity' casting a shadow underneath. The reflectivity can be distinctly differentiated from the blood vessels on the optic nerve. Two patients had an arcuate scotoma on the Humphrey visual fields. No correlation was found between the changes on Spectralis OCT with that of visual field.Spectralis OCT is another useful ancillary investigation in the diagnosis of ONHD and we describe the features in the present study.Optic Nerve Head Drusen (ONHD) are white calcareous deposits that are generally asymptomatic and are bilateral in 66-85% of cases [1]. They are characteristically found in the pre-laminar region of the ONH and are believed to arise from the debris due to long standing axonal stasis in the nerve fibre layer [2]. Histopathologically, the drusen contain multiple deposits of calcium crystals that vary in size (5 to 1000 microns) [2,3]. These crystals mechanically compress the overlying nerve fibre layer resulting in progressive visual field defects [4].The diagnosis of ONHD is based upon a strong index of suspicion and confirmed by B-scan ultrasound of the posterior segment, which shows echodense structure with acoustic shadowing. CT scan may be required in the rare case when ultrasound is inconclusive [1-3]. Time-domain Stratus OCT has been used in recent years to document the nerve fibre layer changes associated with drusen [5]. However, the poor resolution of time-domain OCT prevents the visualization of changes seen as a result of mechanical compression due to the