Pre-laminar tissue thickness measurably affects the visualization of the lamina cribrosa (LC)

Abstract

 

Purpose

 

Concrete effort has recently been made to analyze the LC, as it is considered a primary location for glaucomatous damage. This study evaluated the effect of pre-laminar tissue thickness on LC visualization with OCT.

 

Methods

 

The LC region of 132 eyes (46 healthy, 29 glaucoma suspect, and 57 glaucoma) from 105 subjects was scanned using a prototype swept-source (SS-) OCT at a 1060nm wavelength with a 100kHz axial scan rate. The quality of the scans were graded subjectively using a scale of 1-5. The quality grading was based on pore presence, clarity, and contrast. The pre-laminar tissue thickness of each eye was quantified by measuring the distance between the anterior pre-laminar surface and anterior laminar surface. Pre-laminar tissue thickness was then related to the quality grading using a linear mixed effects model, accounting for the inclusion of both eyes from some subjects.

 

Results

 

Pre-laminar tissue thickness was 85.8±20.8µm thinner in glaucoma suspects (p=0.0001) and 109.4±17.2µm thinner in glaucoma subjects (p=0.0000) compared to normal (Fig. C). Pre-laminar tissue thickness significantly affected the quality of LC visualization, with thicker pre-lamina causing worse LC image quality (p=0.0004, Fig. A, B, D).

 

Conclusions

 

Pre-laminar tissue plays an important role in the visualization of the LC. The constraints created by pre-laminar tissue may present difficulties in properly characterizing LC microstructure in healthy eyes. Therefore, LC microstructure may be better used to analyze longitudinal progression changes in individual subjects instead of as a cross-sectional measurement to determine disease status, until technological advances enable better LC visualization in spite of optically scattering intervening structures.  

 

Figure. (A) Cross-sectional scan of a healthy subject with thick pre-laminar tissue (left, anterior pre-laminar surface - red line, anterior laminar surface - teal line) shows poor LC quality (right) in C-mode. (B) Cross-sectional scan of a glaucoma subject with thin pre-laminar tissue (left) shows good LC quality (right) in C-mode. (C) Boxplot of pre-laminar tissue thickness based on diagnosis and (D) scatterplot of pre-laminar tissue thickness with ranked LC quality.