Excimer laser effects on outflow facility and outflow pathway morphology.

Area of Science:

• Ophthalmology
• Ocular Physiology
• Surgical Innovation

Background:

• Aqueous humor outflow resistance is a key factor in intraocular pressure regulation.
• Understanding the specific anatomical contributions to outflow resistance is crucial for developing effective glaucoma treatments.

Purpose of the Study:

• To quantify the resistance to aqueous humor outflow attributed to tissues located distal to the inner wall of Schlemm's canal.
• To determine the functional significance of the tissues outside Schlemm's canal in regulating ocular fluid dynamics.

Main Methods:

• Human cadaver eyes were perfused at a constant pressure of 10 mm Hg.
• An excimer laser was used to precisely ablate portions of the sclera, exposing Schlemm's canal while preserving its inner wall.
• Outflow facility was measured before and after laser ablation (sinusotomy) to assess changes in resistance.

Main Results:

• A statistically significant increase in outflow facility was observed after excimer sinusotomy (mean increase of 27%).
• This corresponds to a 21.3% reduction in outflow resistance directly measured, and an estimated 35% reduction when accounting for circumferential flow.
• Microscopy confirmed the structural integrity of the inner wall of Schlemm's canal post-ablation.

Conclusions:

• The tissues distal to the inner wall of Schlemm's canal represent a significant component of the total resistance to aqueous humor outflow.
• Approximately one-third of the outflow resistance originates from structures outside the inner wall of Schlemm's canal.
• These findings highlight potential therapeutic targets for enhancing aqueous humor drainage in conditions like glaucoma.