Optic Nerve and Glaucoma: Time for a Paradigm Shift

Introduction: Rethinking What We Thought We Knew

For over a century, glaucoma—the second leading cause of blindness worldwide—has been primarily defined and treated through the lens of intraocular pressure (IOP). Yet as we evolve in our understanding of the disease, so too must our methods of diagnosis, monitoring, and treatment.

This post explores the shifting paradigm in glaucoma care—from a singular focus on pressure to a comprehensive view of optic nerve health—drawing on insights from clinical electrophysiology, microperimetry, and newer therapeutic approaches like selective laser trabeculoplasty (SLT).

From Appearance to Pressure to Function: The Historical Arc

Glaucoma was once diagnosed by what physicians could see from the outside—namely, the "glaucous" (bluish-green) appearance of the eye. The development of tonometry in the mid-20th century revolutionized care, making intraocular pressure a central diagnostic and therapeutic target.

But over time, researchers discovered a critical gap: many patients progressed despite having normal IOP. This uncovered a broader reality—glaucoma is a neurodegenerative disease of the optic nerve, influenced by factors far beyond pressure alone.

A New Framework: Functional Diagnostics in Focus

In 2024, we are witnessing a transformation in the way clinicians assess glaucoma. New functional tools are emerging to supplement structural tests like OCT (Optical Coherence Tomography):

Electrophysiology

Tests like Visual Evoked Potentials (VEP) and Electroretinography (ERG) objectively measure the function of the optic nerve and retina. These tests are particularly valuable when patient-reported vision loss is unreliable or early dysfunction is suspected despite normal imaging.

Microperimetry (Visual Field 2.0)

Unlike traditional perimetry that focuses on peripheral vision, microperimetry hones in on central retinal sensitivity, allowing for earlier detection of damage, especially in macular-involved glaucoma and retinal disease.

Keshav’s Triad: Pressure, Perfusion, and the Brain

Dr. Narain introduces Keshav’s Triad, which identifies three hydrodynamic forces affecting the optic nerve:

1. Systemic Hypotension (low blood pressure)

2. Ocular Hypertension (high eye pressure)

3. Elevated Intracranial Pressure (ICP)

These factors converge at the optic nerve head, affecting its health through mean ophthalmic artery perfusion pressure (mOAP). A patient with normal IOP could still experience optic nerve damage if systemic hypotension or increased ICP is present. This underscores why IOP alone is no longer sufficient for diagnosis or treatment planning.

SLT: A Game-Changing Treatment

Among the most promising therapeutic shifts is Selective Laser Trabeculoplasty (SLT). Unlike daily eye drops, SLT:

• Requires no patient compliance

• Has fewer side effects

• Offers longer-lasting results

• Is cost-effective over time

• Stimulates biological repair of the drainage system (trabecular meshwork)

In many cases, SLT is now being considered as a first-line treatment, especially in settings where access to long-term pharmaceutical care is limited.

Real-World Evidence: What the Data Shows

Case studies presented in Dr. Narain’s lecture illustrate real gains in patients treated with SLT:

• VEP improvements: Post-treatment, patients showed faster signal transmission through the optic nerve.

• Microperimetry tracking: Retinal sensitivity and scotoma mapping provided actionable feedback on treatment effectiveness and disease progression.

Together, these tools offer a dynamic and multidimensional view of glaucoma—moving beyond snapshots of anatomy to real-time insight into function.

New Challenges and Considerations

The evolving landscape of glaucoma management demands updated protocols for complex cases:

• Normal Tension Glaucoma (NTG): Often missed when relying solely on IOP.

• High Myopia: Optic nerve anatomy can be misleading on OCT.

• Non-Arteritic Anterior Ischemic Optic Neuropathy (NA-AION): May mimic or co-exist with glaucoma but requires different treatment.

In these cases, electrophysiology and microperimetry are not luxuries—they are necessities.

Conclusion: A Call to Action

The future of glaucoma care is not just about lowering pressure—it’s about preserving function. As we expand our diagnostic toolbox and refine our understanding of the optic nerve's complex environment, we are better equipped to intervene early, track progression, and personalize treatment.

This shift requires embracing functional diagnostics, laser-first therapy, and a nuanced understanding of each patient's unique physiology.

It’s time we updated our clinical paradigm—before vision loss makes the case for us.

🔍 Frequently Asked Questions

Q: Why is IOP not enough anymore?Because many glaucoma patients progress despite having normal eye pressure. Factors like blood flow to the optic nerve and intracranial pressure matter just as much.

Q: What is microperimetry and how is it different?Microperimetry maps central visual field sensitivity and monitors fixation. It’s more sensitive for detecting macular damage than traditional field tests.

Q: How does SLT compare to eye drops?SLT has fewer side effects, better compliance (since it's done in-office), and may restore fluid drainage mechanisms in the eye.