Open Angle Glaucoma

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Open-angle glaucoma is the most common form of glaucoma and one of the leading causes of irreversible blindness worldwide. It develops slowly over time, often without noticeable symptoms until significant vision loss has occurred. The condition is caused by damage to the optic nerve, typically due to elevated intraocular pressure (IOP) from impaired drainage of aqueous fluid within the eye.

In a healthy eye, aqueous fluid flows continuously through the trabecular meshwork — a microscopic drainage channel located in the angle between the iris and the cornea. In open-angle glaucoma, this drainage angle remains “open,” but the trabecular meshwork becomes partially blocked, leading to a gradual increase in eye pressure and progressive optic nerve damage.

This is the classic and most common form. The drainage system of the eye becomes less efficient over time, increasing pressure and slowly damaging the optic nerve. POAG often develops painlessly and without vision changes until advanced stages.

In this type, optic nerve damage occurs even though eye pressure remains within the normal range. Risk factors such as reduced blood flow to the optic nerve, vascular dysregulation, or genetic predisposition may play a role.

This occurs as a result of another eye condition or external factor—such as inflammation, steroid use, trauma, or pigment dispersion—that obstructs fluid drainage and raises eye pressure.

Because open-angle glaucoma progresses silently, regular comprehensive eye exams are critical for early detection. Diagnosis typically involves:

• Measurement of intraocular pressure (tonometry)
• Examination of the optic nerve (ophthalmoscopy or OCT imaging)
• Visual field testing to detect early vision loss
• Corneal thickness measurement (pachymetry)
• Gonioscopy to assess the drainage angle

Although glaucoma damage cannot be reversed, early and consistent treatment can slow or prevent further vision loss. Treatment focuses on lowering eye pressure to protect the optic nerve.

Selective Laser Trabeculoplasty (SLT) is a highly effective and minimally invasive laser treatment that improves fluid outflow through the trabecular meshwork. It is often recommended as first-line or adjunct therapy and can reduce the need for daily drops.  

Medicated drops are usually the first line of treatment. They work by either reducing fluid production or improving drainage. Common types include prostaglandin analogs, beta blockers, alpha agonists, and carbonic anhydrase inhibitors.

Oral medications for glaucoma are typically used when eye drops and laser treatments are not sufficient to control intraocular pressure (IOP). They are systemic drugs that lower eye pressure by reducing the production of aqueous humor (the fluid inside the eye).

Carbonic Anhydrase Inhibitors (CAIs): These are the primary oral drugs used for glaucoma management. They decrease the production of aqueous humor by inhibiting the enzyme carbonic anhydrase in the ciliary body of the eye.

Common oral CAIs include:

• Acetazolamide (Diamox) – The most widely used oral medication for glaucoma; available in regular and extended-release forms.
• Methazolamide (Neptazane) – Similar mechanism but generally better tolerated with fewer side effects.

MIGS procedures—such as the iStent, Hydrus Microstent, or OMNI canaloplasty—enhance natural drainage pathways with minimal tissue disruption. These are often performed during cataract surgery for added benefit.

In advanced or unresponsive cases, traditional procedures such as trabeculectomy or glaucoma drainage implants(Ahmed or Baerveldt valves) create new drainage pathways to control pressure.