Mathematically modeling the involvement of axons in Leber's hereditary optic neuropathy.
OBJECTIVE
Leber's hereditary optic neuropathy (LHON), a mitochondrial disease, has clinical manifestations that reflect the initial preferential involvement of the papillomacular bundle (PMB). The present study seeks to predict the order of axonal loss in LHON optic nerves using the Nerve Fiber Layer Stress Index (NFL-S(I)), which is a novel mathematical model.


METHODS
Optic nerves were obtained postmortem from four molecularly characterized LHON patients with varying degrees of neurodegenerative changes and three age-matched controls. Tissues were cut in cross-section and stained with p-phenylenediamine to visualize myelin. Light microscopic images were captured in 32 regions of each optic nerve. Control and LHON tissues were evaluated by measuring axonal dimensions to generate an axonal diameter distribution map. LHON tissues were further evaluated by determining regions of total axonal depletion.


RESULTS
A size gradient was evident in the control optic nerves, with average axonal diameter increasing progressively from the temporal to nasal borders. LHON optic nerves showed an orderly loss of axons, starting inferotemporally, progressing centrally, and sparing the superonasal region until the end. Values generated from the NFL-S(I) equation fit a linear regression curve (R(2) = 0.97; P < 0.001).


CONCLUSIONS
The quantitative histopathologic data from this study revealed that the PMB is most susceptible in LHON, supporting clinical findings seen early in the course of disease onset. The present study also showed that the subsequent progression of axonal loss within the optic nerve can be predicted precisely with the NFL-S(I) equation. The results presented provided further insight into the pathophysiology of LHON.
Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
Billy X
BX
Pan
Fred N
FN
Ross-Cisneros
Valerio
V
Carelli
Kelly S
KS
Rue
Solange R
SR
Salomao
Milton N
MN
Moraes-Filho
Milton N
MN
Moraes
Adriana
A
Berezovsky
Rubens
R
Belfort
Alfredo A
AA
Sadun
D000368:Aged; D001369:Axons / Q000473:pathology*; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D008962:Models, Theoretical; D029242:Optic Atrophy, Hereditary, Leber / Q000473:pathology*; D009900:Optic Nerve / Q000473:pathology*; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence