Target IOP Calculator

Target intraocular pressure (IOP) is not derived from a single mathematical formula.
Instead, it is a clinically derived concept based on large longitudinal glaucoma trials demonstrating that lowering IOP reduces the risk of structural and functional progression, with greater reduction required for more advanced disease.

The percentage reductions used in this calculator are informed by the following landmark studies and consensus guidelines:

1. Early Manifest Glaucoma Trial (EMGT)

• Showed that a ~25% IOP reduction reduced the risk of progression in early glaucoma.

• Demonstrated that each 1 mmHg of IOP reduction reduced progression risk by ~10%.

Reference:
Heijl A, Leske MC, Bengtsson B, et al.
Reduction of intraocular pressure and glaucoma progression.
Arch Ophthalmol. 2002;120(10):1268–1279.

2. Collaborative Initial Glaucoma Treatment Study (CIGTS)

• Supported more aggressive IOP lowering in patients with more advanced disease.

• Reinforced the need for individualised target IOP rather than a universal threshold.

Reference:
Lichter PR, Musch DC, Gillespie BW, et al.
Interim clinical outcomes in the CIGTS.
Ophthalmology. 2001;108(11):1943–1953.

3. Advanced Glaucoma Intervention Study (AGIS)

• Demonstrated that patients maintaining IOP consistently <18 mmHg had less visual field deterioration.

• Influenced the concept of lower absolute targets in advanced glaucoma.

Reference:
The AGIS Investigators.
The relationship between control of intraocular pressure and visual field deterioration.
Am J Ophthalmol. 2000;130(4):429–440.

4. European Glaucoma Society (EGS) Guidelines

• Recommends stage-based IOP reduction:

  • Early glaucoma: ~20–25%

  • Moderate glaucoma: ~30%

  • Advanced glaucoma: ≥40%

• Emphasises revising target IOP if progression occurs.

Reference:
European Glaucoma Society.
Terminology and Guidelines for Glaucoma, 5th Edition.
Savona, Italy; 2020.

5. American Academy of Ophthalmology (AAO) Preferred Practice Pattern

• Supports individualised target IOP based on:

  • Disease severity

  • Rate of progression

  • Life expectancy

  • Risk factors (e.g., thin CCT, pseudoexfoliation)

Reference:
American Academy of Ophthalmology.
Primary Open-Angle Glaucoma PPP.
2020–2023 update.

🔎 How this calculator applies these principles

This calculator:

• Uses stage-based percentage IOP reduction (20% / 30% / 40%) as a starting point

• Tightens the target when progression or high-risk features are present

• Applies a safety floor to avoid hypotony risk

• Outputs a target range, not a single absolute number

This mirrors real-world glaucoma management rather than implying a fixed or universally “correct” IOP.

Important disclaimer (recommended to display)

This calculator provides decision support only.
Target IOP must be reassessed over time and adjusted based on documented optic nerve, OCT, or visual field progression, treatment tolerance, and patient-specific risk–benefit considerations.