Clinical features and imaging characteristics in achiasmia

Area of Science:

• Ophthalmology
• Neuroscience
• Developmental Biology

Background:

• Achiasmia is a rare visual pathway maldevelopment characterized by reduced crossing of optic nerve axons at the optic chiasm.
• Understanding the full spectrum of achiasmia's impact on visual structures and brain morphology is crucial for diagnosis and management.

Purpose of the Study:

• To investigate the clinical characteristics, macular, optic nerve, and brain morphology in individuals with achiasmia.
• To identify potential underlying developmental processes and associated anomalies in achiasmia.

Main Methods:

• A prospective, cross-sectional study involving 12 participants with achiasmia and 24 matched healthy controls.
• Comprehensive assessments included ophthalmology exams, eye movement recordings, spectral-domain optical coherence tomography (OCT), visual-evoked responses (VERs), and brain MRI.

Main Results:

• Achiasmia was confirmed by VERs; participants exhibited reduced visual acuity, see-saw nystagmus, and absent stereo vision.
• OCT revealed optic nerve hypoplasia with foveal hypoplasia in some, and macular changes in others.
• MRI showed varying degrees of chiasmatic maldevelopment (aplasia/hypoplasia) in 83% of participants, with some also presenting septo-optic dysplasia.

Conclusions:

• This study identifies neuronal abnormalities at the retinal level in achiasmia for the first time.
• Foveal and optic nerve changes, along with midline brain anomalies, suggest achiasmia may represent a spectrum of fetal developmental abnormalities.