How 3-D imaging shows tissue microstructures

Take-Home Message

Evaluation of the lamina cribrosa, using a three-dimensional imaging technology and a multi-modal adaptive optics imaging system (Physical Sciences Inc.), allows quantification of the microstructural features.

By Lynda Charters; Reviewed by Bo Wang

Wang

Washington, DC-The lamina cribrosa is a primary target of glaucomatous damage. However, advances in optical coherence tomography (OCT) technology permit three-dimensional (3-D) imaging of the tissue, which may be useful to identify glaucomatous damage or progression, said Bo Wang.

A study was conducted by Wang and his colleagues that included 30 glaucomatous eyes and 15 healthy eyes of 45 subjects. Comprehensive examinations were performed, and a multi-modal adaptive optics (AO) imaging system with spectral-domain optical coherence tomography (SD-OCT) and scanning laser ophthalmoscopy (SLO) (Physical Sciences Inc.) were used to image the lamina cribrosa.

The axial resolution of the system was 4 μm and the transverse resolution with AO was 4.5 μm. There were 28,000 A-scans/second obtained, said Wang, who is a student at the University of Pittsburgh Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh.

The instrument has a 1,050-nm superluminescent diode source with an 85-nm bandwidth.

A subset of the patients underwent imaging using a commercially available SD-OCT (Spectralis, Heidelberg Engineering) or high-definition OCT (Cirrus, Carl Zeiss Meditec) and confocal scanning laser ophthalmoscopy (HRT-III, Heidelberg Engineering).

Glaucoma was diagnosed before the study based on the presence of a reproducible and characteristic visual field (VF) defect.

The study sought to examine the 3-D in vivo structural characteristics of the lamina cribrosa using the AO imaging system and evaluate the tissue’s spatial relationship with VF function and retinal nerve fiber layer (RNFL) loss.

Findings

Using the AO imaging system, Wang said, the pores of the lamina cribrosa were discernible in individual C-mode slices and could be followed in 3-D through a stack.

Automated quantitative analysis can be performed on the microstructures of the lamina cribrosa, such as analyzing beam thickness and pore diameter.

In contrast, the commercial Cirrus and HRT imaging devices showed qualitatively poorer resolution of the lamina cribrosa beams and pores.

Spectralis did not permit dense 3-D reconstruction of the lamina cribrosa due to lower scan density and long scan time.

Morphologic indentation in the anterior surface of the lamina cribrosa was observed using both commercial SD-OCT and the AO SD-OCT device with limited correspondence with the VF or RNFL anomalies. This discrepancy was noted with anterior surface indentations of the lamina cribrosa identified in healthy controls and patients with glaucoma that do not correspond to locations of the VF and RNFL loss.

There was great variability in the pore size, shapes, and orientations in both healthy and glaucomatous eyes.

That comprehensive analysis of the lamina cribrosa, Wang said, involved consideration of the 3-D microstructures.

High-resolution AO SD-OCT permits more detailed 3-D reconstruction of the microstructure of the lamina cribrosa compared with devices that are commercially available.

“The lamina cribrosa is an important and often-observed structure in the study of glaucoma, but appropriate analysis should consider its 3-D nature, and subsequent quantification of the microstructural features,” Wang said. “The AO SD-OCT system allows for detailed 3-D lamina cribrosa analysis on a micro-scale that would advance the understanding of the glaucomatous pathogenesis.”

Bo Wang

E: wangb4@upmc.edu

Bo Wang has no proprietary interest in this subject matter.

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