Cytoskeletal Alteration and Change of Retinal Nerve Fiber Layer Birefringence in Hypertensive Retina

ABSTRACT

Purpose: Glaucoma damages the retinal nerve fiber layer (RNFL). Both RNFL thickness and retardance can be used to assess the damage, but birefringence, the ratio of retardance to thickness, is a property of the tissue itself. This study investigated the relationship between axonal cytoskeleton and RNFL birefringence in retinas with hypertensive damage.

Materials and Methods: High intraocular pressure (IOP) was induced unilaterally in rat eyes. RNFL retardance in isolated retinas was measured. Cytostructural organization and bundle thickness were evaluated by confocal imaging of immunohistochemical staining of the cytoskeletal components: microtubules (MTs), F-actin, and neurofilaments. Bundles with different appearances of MT stain were studied, and their birefringence was calculated at different radii from the optic nerve head (ONH) center.

Results: Forty bundles in eight normal retinas and 37 bundles in 10 treated retinas were examined. In normal retinas, the stain of axonal cytoskeleton was approximately uniform within bundles, and RNFL birefringence did not change along bundles. In treated retinas, elevation of IOP caused non-uniform alteration of axonal cytoskeleton across the retina, and distortion of axonal MTs was associated with decreased birefringence. The study further demonstrated that change of RNFL birefringence profiles along bundles can imply altered axonal cytoskeleton, suggesting that ultrastructural change of the RNFL can be inferred from clinical measurements of RNFL birefringence. The study also demonstrated that measuring RNFL birefringence profiles along bundles, instead of at a single location, may provide a more sensitive way to detect axonal ultrastructural change.

Conclusions: Measurement of RNFL birefringence along bundles can provide estimation of cytoskeleton alteration and sensitive detection of glaucomatous damage.

KEYWORDS:

• Birefringence
• cytoskeleton
• microtubules
• glaucoma
• retinal nerve fiber layer

Funding

This study was supported by NIH grant R01-EY019084, NIH center grant P30-EY014801, and an unrestricted grant from Research to Prevent Blindness, Inc.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

Additional information

Funding

This study was supported by NIH grant R01-EY019084, NIH center grant P30-EY014801, and an unrestricted grant from Research to Prevent Blindness, Inc.