Rethinking Glaucoma Care: Understanding Optic Nerve Damage and What We Thought We Knew

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).

A surreal, distorted image captures multiple overlapping faces, creating a kaleidoscopic effect that evokes a sense of dreamlike introspection and fragmented reality.

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 Optic Nerve Damage

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

• Systemic Hypotension (low blood pressure)

• Ocular Hypertension (high eye pressure)

• 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.