Glaucoma - AIOS D B Chandra Disha Award - aioseducation

69th AIOC Proceedings, Ahmedabad 2011
This paper was conferred with the AIOS D B CHANDRA - DISHA
AWARD for the BEST PAPER of ALL GLAUCOMA Sessions. This
paper was also judged the BEST PAPER of GLAUCOMA-I Session.
DR. VINAY KUMAR NANGIA B: M.B.B.S. (’80) & M.S. (’84) from Govt.
Medical College, Nagpur University; Fellowship (’86), FRCS (’89). Formerly,
Fellow and Consultant, Vitreo Retinal Surgery, Medial Research Foundation,
Madras, Sankara Nethralaya, Chennai; Resident Ophthalmology, Royal Eye
Hospital, Manchester, U.K. Presently, Director, Suraj Eye Institute, Nagpur.
Contact: 9890020804
Measurement of Neural Canal Using the Spectral
Domain OCT
Dr. Vinay Kumar Nangia B., Dr. Shubhra Agarwal, Dr. Karishma Bhate,
Dr. Rajesh Gupta
Purpose: The neural Canal is the area between the edges of the bruchs membrane. It was
the purpose to measure the diameter of the neural canal in the human eye using spectral
domain enhanced digital imaging technology. Methods: 11 eyes of 6 patients who underwent
OCT for RNFLT were included. Mean age was 59.83+16.36. There were 5 males and 1

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female. Enhanced Depth Imaging with the spectralic OCT was used to image the optic disc
using a horizontal scan. Edges of the bruchs membrane were identified and measured using
planimetry. Results: The mean diameter of the neural canal was 1.61+0.21 mm. (range 1.32-
1.88) The mean disc area was 3.39mm2. The neural canal area was significantly correlated
with disc area (p=0.019;r=0.794), cup area (p=0.005;r=0.87), CCT (p=0.042;r=0.619) and with
age (pO.047;r=-0.887). Discussion: Neural Canal measurement is now possible. Neural Canal
characteristics may be important in the study of optic disc morphometry in health and disease.
The neural Canal is the area between the edges of the bruchs membrane. The
lamina cribrosa fills up the space between the bruchs membrane through
which the optic nerve fibers pass. The neural canal and the lamina cribrosa are
important anatomic landmarks, that may have a significant role to play in the
health of the optic nerve and in explaining the aetiopathogenesis of optic nerve
disease. 1,2 It was the purpose to measure the diameter of the neural canal in the
human eye using spectral domain enhanced digital imaging technology.
MATERIALS AND METHODS
11 eyes of 6 subjects who underwent spectral domain OCT for Retinal nerve fiber
layer thickness were included. There were 5 males and 1 female. The mean
age was 59.83+-16.36 yrs. The spectralis from Heidelberg engineering was used
with V 5.3.1 software. Enhanced depth horizontal imaging of the optic disc
was done for increased penetration through the optic nerve. This was achieved
by bringing the OCT lens closer to the eye. This causes greater depth imaging
and enables visualization of the optic nerve and the choroid. The ends of the
Bruchs membrane was identified visually. Using the drawing and measuring tool
available in the software, the edges of the bruchs membrane in the horizontal
and diagonal planes were identified and measured planimetrically. The These
measurements were considered as the horizontal and diagonal measurements of
the neural canal.
RESULTS
The mean diameter of the neural canal horizontal diameter was 1.61+-0.21mm.
(range 1.32,1.88) and diagonal was 1.61+-0.21 mm (range 1.31, 1.88). The mean
disc area was 3.39mm2 (range 2.61, 4.66) and the mean cup area was 1.80+-
0.57mm. (range 1.10, 2.56). The neural canal diameters (horizontal and diagonal)
showed positive significant correlations with disc area (p=0.1;r=0.8), cup area
(p=0.001;r=0.9), and negative significant correlations with central corneal
thickness (p=0.042+-0.619) and age (p=0.047;r=-0.88) There was no significant
bivariate correlation with tilt of disc along vertical axis, cup disc ratio, spherical
equivalent and axis of astigmatism. Multivariate regression analysis with the
horizontal neural canal diameter as dependant parameter and disc area, cup
area, CCT, and age as independent variables showed significant correlations
with cup area (p=0.05) and CCT (p=0.043).

69th AIOC Proceedings, Ahmedabad 2011
DISCUSSION
The anatomy of the optic disc is important since it is the primary focus of
damage and the first structure to manifest sign of glaucomatous change. The
neural canal can only be identified on histology. With the availability of high
resolution spectral domain optical coherence tomography, it has become possible
to visualize the living histology. Using the Enhanced.
Depth Imaging Technique of the Spectralis it was possible to image in depth
the optic nerve head and beyond. Hence it is easy to visually identify the ends
of the Bruchs membrane at the borders of the optic disc. Measurement of the
neural canal is possible manually using the planimetric method in the software.
The study has small numbers. However clinically and on bivariate analysis we
know that it correlates with the optic nerve head and with the cup area, since the
cup area is a covariate of the optic disc area. Its correlations with central corneal
thickness and age need further study. Technology now offers an opportunity to
study the optic nerve in the human eye and the measurements of the neural canal
may give further insight into the ocular and systemic correlations of the optic
nerve in health and disease.
REFERENCES
1. Jonas JB, Berenshtein E, Holbach L. Anatomic relationship between lamina
cribrosa, intraocular space, and cerebrospinal fluid space. Invest Ophthalmol Vis Sci.
2003;44:5189–95.
2. Anthony J. Belleza, Rintalan CJ, Thompson HW, Downs D, et al. Deformation of
the Lamina Cribrosa and the Anterior Scleral Canal Wall in Early Experimental
Glaucoma. Invest Ophthalmol Vis Sci. 2003:44;623-36.