Microvasculature dropout picked out the preperimetric eyes that went on to lose field

Design

subgroup analysis of a prospective longitudinal cohort, mean follow-up 4.9 years

Population

93 eyes of 70 participants with glaucomatous discs and no repeatable field defect; mean age 67.7 years

Primary outcome

rate of circumpapillary capillary density and retinal nerve fibre layer loss, and development of visual field loss

Effect

capillary density -0.88 %/year with dropout against -0.23 without; no difference in nerve fibre layer loss (P=0.886); field loss in 62.5% against 26.2% (P<0.001)

Preperimetric glaucoma - a glaucomatous disc with no repeatable field defect - is the hardest follow-up decision in the clinic, because most of these eyes will not convert and the ones that will are not obvious. This subgroup analysis of a prospective cohort followed 93 eyes in 70 participants for a mean of 4.9 years with optical coherence tomography, OCT angiography and visual fields, grouped by whether microvasculature dropout was present at baseline.

Thirty-two eyes had dropout. They lost circumpapillary capillary density more than three times faster (-0.88 %/year, 95% CI -1.08 to -0.67, against -0.23 %/year, -0.42 to -0.04), and the association held in multivariable models (-0.63 %/year, -0.95 to -0.32, P<0.001). Retinal nerve fibre layer thinning did not differ at all (0.03 µm/year, -0.33 to 0.38, P=0.886). Most importantly, visual field loss developed in 62.5% of eyes with dropout against 26.2% without (P<0.001).

That dissociation - vascular change progressing while structural thinning does not - is the interesting part, and it also flags the limitation: if the nerve fibre layer is unchanged, the capillary density measurement may partly be detecting something other than neural loss. Ninety-three eyes from 70 people is small, and OCT angiography is not universally available. But where it is, this identifies a subgroup in which two out of three eyes converted within five years, and those are eyes that should be seen more often than annually.

• Where OCT angiography is available, look for microvasculature dropout when deciding follow-up interval in preperimetric glaucoma
• Shorten the interval and perform fields more often in eyes with dropout - nearly two-thirds converted within five years
• Do not rely on stable retinal nerve fibre layer thickness for reassurance in these eyes; it did not differentiate
• Treat this as risk stratification rather than as an indication to start treatment on its own
• Note the cohort was small and from a specialist centre - the conversion rates will not transfer directly

Why it matters

It offers a way to decide which preperimetric eyes need close follow-up, in the one situation where structural monitoring is least informative.

Don't overread it

A subgroup analysis of 93 eyes at a specialist centre - it stratifies risk, and does not show that acting on the stratification improves outcomes.

The statistics, in plain English

The capillary density difference (-0.88 against -0.23 %/year) has non-overlapping confidence intervals, so the difference in rate is solid within this cohort. The conversion figures are the more useful ones clinically, but with 32 eyes in one group and 61 in the other, 62.5% means 20 eyes - so treat it as 'most' rather than as a precise probability. The null result for retinal nerve fibre layer loss is worth noticing: it means this marker adds information that conventional structural monitoring does not, which is the whole argument for measuring it.

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