OCT yields comparable optic nerve head, RNFL scans in sitting, supine positions

Issue: November 25, 2012

A portable spectral-domain optical coherence tomography device provided optic nerve head and retinal nerve fiber layer thickness measurements that were similar in both sitting and supine positions, a study found.

Researchers at University of California, San Diego, demonstrated the reliability and repeatability of measurements taken with the portable iVue spectral-domain OCT system (Optovue).

“This device was one of two spectral-domain devices at that time and at the present time that can take measurements in the sitting position and also the supine position,” Kaweh Mansouri, MD, MPH, the corresponding study author, told Ocular Surgery News. “Therefore, we wanted to see if the measurements changed specifically with the positions. The main finding was that they did not.”

Posture-related fluctuations in IOP may exceed 5 mm Hg and skew OCT measurements, Mansouri and colleagues said in the study published in the American Journal of Ophthalmology.

Kaweh Mansouri

Patients and methods

The prospective study included 60 eyes of 30 patients: 10 healthy young adults with a mean age of 22.9 years, 10 healthy older adults with a mean age of 53.9 years and 10 primary open-angle glaucoma patients with a mean age of 61.3 years.

Investigators obtained five scans in the sitting position and five in the supine position from all patients. Retinal nerve fiber layer (RNFL) thickness values were obtained from a 3.45-mm circle centered on the optic disc.

Repeatability and correlations between measurements obtained in sitting and supine positions were assessed for four optic nerve head (ONH) parameters (optic disc area, cup area, rim area and rim volume) and three RNFL thickness parameters (inferior, superior and overall average thickness). Repeatability was defined as the variation of repeat measurements in the same position.

Results and observations

Study results showed high reliability within individual eyes. Intraclass correlation coefficients ranged from 73% to 99% for ONH parameters and 72% to 99% for RNFL parameters.

Concordance correlation coefficients between supine and sitting ONH measurements were 97% to 99% in younger healthy patients, 98% to 99% in older healthy patients and 84% to 99% in glaucoma patients.

“The repeatability itself is quite good,” Mansouri said. “It has to do with the scanning rate of the device and the high resolution of the device, which is identical to the RTVue spectral-domain OCT made by the same company.”

The ONH rim area measurement was the least repeatable, the study authors said.

The iVue is suited for retinal imaging in children and patients with physical disabilities who cannot undergo scanning in a sitting position, Mansouri said.

In addition, the system may be used to take measurements in zero gravity conditions.

“There are findings that astronauts have been losing vision because of intraocular pressure changes,” Mansouri said. “We could use OCT imaging in space to find out what is happening in astronauts’ eyes.” – by Matt Hasson

Reference:

Mansouri K, Liu JHK, Tafreshi A, Medeiros FA, Weinreb RN. Positional independence of optic nerve head and retinal nerve fiber layer thickness measurements with spectral-domain optical coherence tomography. Am J Ophthalmol. 2012;154(4):712-721.

For more information:

Kaweh Mansouri, MD, MPH, can be reached at Hamilton Glaucoma Center, University of California, San Diego, Department of Ophthalmology, 9500 Gilman Drive, La Jolla, CA 92093-0946; email: kawehm@yahoo.com.
Disclosure: Mansouri has no relevant financial disclosures.