The Relationship Between NAION and Refractive Error
The Relationship Between NAION and Refractive Error
Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic neuropathy in patients older than the age of 50 years. Although the precise cause is not known, vascular risk factors, including hypertension, diabetes mellitus, and hypercholesterolemia are thought to predispose the patient to ischemia of the optic nerve head. Despite these conditions, another important predisposing risk factor is the presence of a small optic disk and cup, with a small cup-to-disk ratio (CDR). The authors of this cohort study reviewed the records of 608 patients with NAION seen from 1973 to 2000 to determine whether refractive error was related to CDR. The previous literature attempting to link refractive error with CDR in NAION has shown conflicting results.
Hayreh SS, Zimmerman MB
Ophthalmology. 2008;115:2275-2281
Spherical equivalent refraction was used to determine refractive error. There was an association between CDR and age for patients 50 years of age and older. Compared with a reference age-matched population, there was a higher proportion of NAION eyes with spherical equivalents between -0.5 and +0.5 diopters. The number of patients with refractions between -3D to less than -0.5D, and between +0.5D and +3D, were smaller than expected. Thus, a higher degree of myopia or hyperopia was associated with a larger horizontal CDR.
The size of the optic disk and cup are determined in development. It is believed that a small optic disk and cup perpetuate ischemia via the compression of adjacent swollen axons. The authors reviewed what they believe is the sequence of events underlying ischemic optic neuropathy through this process and emphasized that they believe the anatomically small CDR is a secondary contributing factor, rather than the primary factor, involved in this optic neuropathy.
Abstract
Introduction
Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic neuropathy in patients older than the age of 50 years. Although the precise cause is not known, vascular risk factors, including hypertension, diabetes mellitus, and hypercholesterolemia are thought to predispose the patient to ischemia of the optic nerve head. Despite these conditions, another important predisposing risk factor is the presence of a small optic disk and cup, with a small cup-to-disk ratio (CDR). The authors of this cohort study reviewed the records of 608 patients with NAION seen from 1973 to 2000 to determine whether refractive error was related to CDR. The previous literature attempting to link refractive error with CDR in NAION has shown conflicting results.
Hayreh SS, Zimmerman MB
Ophthalmology. 2008;115:2275-2281
Summary
Spherical equivalent refraction was used to determine refractive error. There was an association between CDR and age for patients 50 years of age and older. Compared with a reference age-matched population, there was a higher proportion of NAION eyes with spherical equivalents between -0.5 and +0.5 diopters. The number of patients with refractions between -3D to less than -0.5D, and between +0.5D and +3D, were smaller than expected. Thus, a higher degree of myopia or hyperopia was associated with a larger horizontal CDR.
Comment
The size of the optic disk and cup are determined in development. It is believed that a small optic disk and cup perpetuate ischemia via the compression of adjacent swollen axons. The authors reviewed what they believe is the sequence of events underlying ischemic optic neuropathy through this process and emphasized that they believe the anatomically small CDR is a secondary contributing factor, rather than the primary factor, involved in this optic neuropathy.
Abstract