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Editors Selection IGR 21-4

Anatomical Structures: Optic Disc

Comment by Andrew Tatham on:

Acquired optic disc pits (ODPs) are localized defects of the lamina cribrosa (LC), which may be a manifestation of, or perhaps, contribute to, glaucomatous structural change. Although recognized as an important clinical sign, there is poor understanding of the relationship between ODPs and glaucomatous neural loss.

This longitudinal study sought to examine rates of change in retinal nerve fiber layer (RNFL) over time in eyes with and without ODPs.

One hundred sixty-three glaucomatous eyes were included, comprising 83 eyes with ODPs and 80 without, followed for an average of just over three years. There were strict criteria for identification of ODPs, which were required to be visible on baseline stereoscopic disc photographs and confirmed at the final visit by the presence of an alteration of the LC at the corresponding location on swept source OCT. Only ODPs involving the temporal LC were included due to the difficulty of imaging the nasal LC. Eyes in the non-ODP group were required to have no focal abnormality of the LC on OCT as this may represent a ‘microscopic ODP’.

Eyes with ODPs experienced faster rates of RNFL loss, with comparatively faster rates in regions corresponding to the location of the ODP. The average rate of RNFL loss in eyes with ODPs was 0.51 µm per year faster than in eyes without an ODP (-1.44 versus -0.93 µm per year, P = 0.008). This result suggests that detection of ODPs may help better predict the rate and location of future structural change.

Interestingly, RNFL loss also appeared to be faster in eyes with partial thickness compared to full thickness LC defects. It was proposed that retinal ganglion cell axons in eyes with partial thickness defects might be subject to greater mechanical stress and strain due to a steeper translaminar pressure gradient, whereas the pressure gradient may be decreased where LC is nonexistent.

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