Quantitative analysis of optic nerve damage in idiopathic intracranial hypertension (IIH) at diagnosis

Optic neuropathy secondary to idiopathic intracranial hypertension (IIH) may be a severe complication which must be early identified, adequately monitored and treated to avoid blindness. The aim of this study was to quantify optic nerve involvement at time of diagnosis in a prospectively series of IIH investigated at a single Institution and to identify objective parameters for early diagnosis and follow-up. 38 consecutive patients (9 men, 29 females, mean age 39.8 years) with IIH underwent a complete neuro-ophthalmological evaluation including standardized automated perimetry as functional measurement of optic neuropathy and spectral domain optical coherence tomography (SD-OCT) measurements to grade papilledema or optic nerve atrophy. An overall diagnosis of optic nerve involvement was made in 50 out of 76 eyes (66 %); ophthalmoscopic signs of papilledema were identified in 35 eyes (46 %) while optic disc pallor was found in 13 (17 %). In all patients mean visual field deviation (MD, dB) was -7.2 (range 5.3-33.2). SD-OCT measurements of peripapillary retinal nerve fiber layer thickness (PRNFLT) and of macular ganglion cell complex thickness (MGCCT) obtained in 40 eyes (20 subjects) showed normal PRNFLT in 12 eyes (30 %), increased in 16 (40 %) and reduced in 12 eyes (30 %); normal MGCCT in 26 eyes (65 %), reduced in 14 (35 %). In all eyes average RNFLT was increased (mean 130 μm, range 219-59) and average MGCCT was decreased compared to normal values (mean 89.5 μm, range 198-65). Increased PRNFLT was associated with reduced MGCCT in 4 eyes (10 %) indicating early retrograde optic nerve damage. Decreased PRNFLT was associated with decreased MGCCT in 10 eyes (83 %). These results indicate that, in IIH patients, signs of optic neuropathy can be identified in more than half of cases, even without papilledema evidenced on ophthalmoscopic examination. Moreover, an SD-OCT analysis, which can be definitively useful to quantify optic nerve edema or atrophy, can show damage of retinal ganglion cells in an early phase of the disease.