Ocular Hypertension and Glaucoma are often used interchangeably, but they represent distinctly different states of eye health. Both conditions involve measuring Intraocular Pressure (IOP), the pressure inside the eye. However, only one is classified as a disease that causes permanent vision loss. The fundamental distinction lies in whether the elevated pressure has begun to inflict measurable harm on the optic nerve and internal eye structures.
Understanding Intraocular Pressure
Intraocular Pressure (IOP) is the fluid pressure maintained within the eyeball, measured in millimeters of mercury (mmHg). This pressure is established by a continuous flow of aqueous humor, a clear fluid produced by the ciliary body. The aqueous humor circulates to nourish structures and then drains out through the trabecular meshwork.
The balance between fluid production and drainage dictates the level of IOP. A healthy IOP range is typically between 10 and 21 mmHg. Maintaining pressure within this window keeps the eye structurally stable and supports the optic nerve’s health. If the drainage system becomes sluggish or blocked, fluid accumulates, causing the pressure to rise.
Ocular Hypertension: Elevated Pressure Readings
Ocular Hypertension (OHT) is a diagnostic term used when the IOP consistently exceeds the normal range, usually above 21 mmHg, without evidence of corresponding damage. It is not considered a disease but a risk factor for developing glaucoma. Patients with OHT do not experience symptoms, as the elevated pressure itself does not cause noticeable vision changes.
The diagnosis requires a thorough examination to ensure the optic nerve appears healthy and visual field tests are normal. The absence of visual field loss or structural changes to the optic nerve distinguishes OHT from glaucoma. Individuals with OHT are classified as “glaucoma suspects” and are monitored closely due to the high pressure. This state is medically coded under the ICD-10 range H40.05.
Glaucoma: The Optic Nerve Disease
Glaucoma is a group of eye diseases characterized by progressive damage to the optic nerve, resulting in irreversible vision loss. It is fundamentally an optic neuropathy—a disease of the nerve that transmits visual information to the brain. While Glaucoma is frequently associated with high IOP, optic nerve damage is the defining characteristic separating it from Ocular Hypertension.
Sustained pressure can cause the death of nerve fibers, leading to a noticeable cupping or excavation of the optic disc, visible upon examination. This gradual deterioration typically affects peripheral vision first, often progressing without the patient’s awareness. Importantly, some forms, like normal-tension glaucoma, cause nerve damage even when IOP measurements fall within the normal 10 to 21 mmHg range. This demonstrates that physical damage, not the pressure reading alone, marks the disease. Glaucoma diagnoses fall within the ICD-10 code range of H40.1 to H40.9.
Management and Monitoring Strategies
The management of Ocular Hypertension differs significantly from the treatment necessary for diagnosed Glaucoma, reflecting the distinction between a risk factor and an active disease. For patients with OHT, the initial strategy often involves watchful waiting, meaning frequent monitoring of IOP, the optic nerve, and visual fields. Risk stratification, including measuring corneal thickness, helps determine the necessity of intervention.
If the specialist determines the risk of progression to glaucoma is high, preventive treatment may be initiated, usually with prescription eye drops to lower the IOP. Conversely, a Glaucoma diagnosis necessitates immediate intervention to prevent further vision loss. Treatment centers on lowering the IOP to stop optic nerve damage from advancing, often using daily eye drops that decrease fluid production or increase drainage. If medication is insufficient, the doctor may recommend laser treatments, such as trabeculoplasty, or surgical procedures to create alternative drainage paths.