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Despite glaucoma being the second leading cause of blindness globally, its pathogenesis remains incompletely understood. Although intraocular pressure (IOP) contributes to glaucoma, and reducing IOP slows progress of the disease, some patients progress despite normal IOP (NTG). Glaucomatous damage causes characteristic cupping of the optic nerve where it passes through the lamina cribrosa. There is evidence that cerebrospinal fluid (CSF) within the optic nerve sheath has a different composition from CSF surrounding the brain. Furthermore, fluctuations in CSF flow into the optic nerve sheath may be reduced by trabeculae within the sheath, and on standing intracranial pressure (ICP) within the sheath is stabilised at around 3 mmHg due to orbital pressure. Blood pressure has been linked both to glaucoma and ICP. These facts have led some to conclude that ICP does not play a role in glaucoma. However, according to stress formulae and Laplace's Law, stress within the lamina cribrosa is dependent on the forces on either side of it, (IOP and ICP), and its thickness. On lying flat at night, ICP between the brain and optic nerve sheath should equalise. Most evidence suggests ICP is lower in glaucoma than in control groups, and that the lamina cribrosa is thinner and more posteriorly displaced in glaucoma. Subjects who have had ICP reduced have developed signs of glaucoma. This review finds most evidence supports a role for low ICP in the pathogenesis of glaucoma. Caffeine, theophylline and vitamin A may increase ICP, and could be new candidates for an oral treatment. MethodologyPubMed was searched online using the combinations of terms: glaucoma, intracranial pressure, cerebrospinal fluid pressure, translaminar pressure gradient, lamina cribrosa, and blood pressure. Abstracts were screened and articles read if considered relevant.

Purpose To establish the prevalence and heritability of cilioretinal arteries (CRAs), tilted discs (TDs) and situs inversus (SI). Methods Fundus photos from the Twins UK Adult Twin registry twin database were analyzed: 1812 individuals, 526 complete monozygotic (MZ) twin pairs and 336 complete dizygotic (DZ) pairs. Images were assessed non-stereoscopically on a computer screen by the same ophthalmologist for presence of CRAs, TDs or SI. Prevalence figures, probandwise concordances and heritabilities were calculated. Results Prevalence of a CRA in subjects' right eyes was 28.6% (26.5-30.8). Prevalence of subjects with a CRA in at least one eye was 45.0% (42.6-47.5), with a TD in at least one eye was 1.2% (0.8-1.9), and with SI at least one eye was 0.5% (0.3-1.0). There was no association between birth weight and presence of CRA.Concordance for CRA in at least one eye (MZ twins) was 60% (95% CI 55-64), and (DZ) was 45% (95% CI 39-51). Heritability for CRAs in at least one eye was 49.4% (95% CI 38.1-59.7) and for both eyes was 32.9% (95% CI 10.4-53.3). We were unable to calculate meaningful heritabilities or concordances for TDs and situs SI, due to insufficient numbers. Conclusions The presence of CRAs appears to be moderately heritable, with greater variance explained by individual environmental factors or even stochastic events. They were not associated with low birth weight. Future genetic research and studies of birth/lifecourse cohorts may offer further insights into the etiology of congenital papillovascular abnormalities.