Optic nerve sheath fenestration using a Raman-shifted alexandrite laser

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Laser Surgery

Background:

• Idiopathic intracranial hypertension can cause optic nerve damage due to overpressure.
• Optic nerve sheath fenestration is a surgical procedure to relieve this pressure.
• Previous studies demonstrated endoscopic free-electron laser use for optic nerve fenestration.

Purpose of the Study:

• Evaluate the efficacy of a table-top Raman-shifted alexandrite (RSA) laser for optic nerve sheath fenestration.
• Assess the feasibility of endoscopic delivery of mid-infrared laser pulses for this procedure.
• Determine optimal laser parameters and evaluate the safety and accuracy of the fenestration process.

Main Methods:

• Porcine optic nerves were ablated using an RSA laser at mid-infrared wavelengths (6.09, 6.27, 6.43 μm).
• Endoscopic beam delivery was achieved using hollow-glass waveguides.
• Ablation thresholds, etch rates, and fenestration efficacy were evaluated using optical coherence tomography and histology.

Main Results:

• The RSA laser effectively fenestrated porcine optic nerves via endoscopic delivery, with optimal performance at 6.09 μm.
• Ablation thresholds were 0.8 ± 0.2 J/cm², and etch rates were 1-4 μm/pulse with minimal thermal damage.
• Fenestration depth control was variable, with 16 good, 23 too deep, and 9 too shallow outcomes in 48 excised nerves.

Conclusions:

• Mid-infrared pulses from the RSA laser, delivered via hollow waveguides, can cut optic nerve sheaths effectively.
• Wavelengths of 6.09 or 6.27 μm are suitable, with 6.09 μm preferred.
• While ex vivo depth control was challenging, the absence of cerebrospinal fluid in excised nerves may underestimate in vivo safety margins.