New findings from a study published in Eye outlined six optic disc phenotypic classifications found in primary open-angle glaucoma (POAG), each linked with unique patient characteristics.
Give me some background first.
In 1996, Stephen Drance, MD, and Marcelo Nicolela, MD published a notable study that designated the appearance of the optic disc into four phenotypes:
- Focal ischemic discs
- Myopic glaucomatous discs
- Senile sclerotic discs
- Generalized enlargement of the optic cup discs
Since then, research has uncovered further optic disc phenotypes, such as a pit-like area of ectasia in the lamina cribrosa, which, if factored into future classifications, would be beneficial to glaucoma specialists.
Talk about the study.
The retrospective interventional case series included 885 eyes from 885 patients that presented to an outpatient tertiary care center and met specified criteria for POAG.
Optic disc photographs were categorized by three glaucoma specialists into the following phenotypes (based on their dominant features):
- Concentric rim thinning
- Focal rim thinning
- Acquired pit of the optic nerve (APON)
- Tilted
- Extensive peripapillary atrophy (PPA)
- Broad rim thinning
And the prevalence of these phenotypes?
The distribution of phenotypic characteristics was as follows:
- Concentric rim thinning: 153 eyes (18%)
- Focal rim thinning: 398 eyes (45%)
- APON: 25 eyes (3%)
- Tilted: 109 eyes (12%)
- Extensive PPA: 47 eyes (5%)
- Broad rim thinning: 153 eyes (17%)
Go on…
Investigators noted a higher proportion of female patients with focal thinning (p=0.015).
Additionally, myopia (p=0.000), Asian race (odds ratio 8.8, p=0.000), and younger age (p=0.000) were linked with the tilted phenotype.
The cohort with focal thinning had a localized visual field pattern with high-pattern standard deviation (PSD) in comparison to those in the concentric thinning group (p=0.005).
Any other connections?
Patients categorized with the concentric thinning phenotype had a thicker RNFL (p=0.000), higher mean deviation (p=0.008), and lower PSD (p=0.043) than broad thinning—despite the fact that no difference in disc sizes (p=0.849) was observed.
Expert opinion?
According to the study authors, “In an era of emerging technologies and increased access to a variety of devices to aid our diagnostic ability, we believe medical semiology remains an important tool for glaucoma specialists.”
Take home.
With further research and refinement, these optic disc phenotypes could allow for eye care practitioners to utilize an enhanced identification system of genetic associations to create individualized treatments for glaucoma patients.