What is the recommended treatment approach for normal‑tension glaucoma in an adult over 40 with intra‑ocular pressure already within the normal range?

Normal-Tension Glaucoma Treatment

For adults over 40 with normal-tension glaucoma (NTG), initiate IOP-lowering treatment targeting at least a 30% reduction from baseline or achieving IOP ≤10-12 mmHg, with prostaglandin analogs as first-line therapy.

Treatment Rationale and Target IOP

Even though IOP is already within the "normal" range (<21 mmHg), lowering IOP remains the only proven modifiable intervention to prevent vision loss in NTG 1, 2. The goal is to reduce IOP sufficiently to prevent disabling visual loss over the patient's lifetime.

Specific IOP Targets:

• Aim for 30% reduction from baseline IOP 1
• Target absolute IOP of 10-12 mmHg 1
• Optimal postoperative target: ≤10 mmHg based on surgical outcomes showing 92.7% visual field stability with >20% IOP reduction 3

The evidence is clear: a 20% IOP reduction achieved visual field stability in 70% of NTG eyes, while inadequately controlled eyes all progressed 3.

First-Line Medical Therapy

Start with prostaglandin analogs as initial treatment 4, 5. These are recommended because they:

• Provide the most effective IOP lowering (20-24% reduction at peak) 6
• Require only once-daily dosing, improving adherence
• Have favorable safety profiles
• Are well-tolerated long-term

Specific agents and their efficacy in NTG:

• Latanoprost: 20% peak reduction, 20% trough reduction 6
• Bimatoprost: 21% peak reduction, 18% trough reduction 6

Alternative and Adjunctive Agents

If prostaglandin analogs are contraindicated, not tolerated, or insufficient:

Second-line options 4, 5:

• Beta-blockers (timolol): 15% peak, 18% trough reduction 6

  • Avoid nighttime dosing - associated with nocturnal BP reduction and potential visual field progression 5
  • Consider cardioselective agents (betaxolol) for patients with pulmonary disease

• Alpha-2 agonists (brimonidine): 24% peak, 11% trough reduction 6

  • Contraindicated in breastfeeding mothers (risk of apnea in infants) 5

• Carbonic anhydrase inhibitors (dorzolamide): 14% peak, 12% trough reduction 6

• Rho kinase inhibitors (netarsudil): 10-20% IOP reduction 5

Surgical Considerations

Laser trabeculoplasty can be considered as primary therapy or when medication adherence, cost, side effects, or convenience are concerns 4, 5. The LiGHT trial demonstrated patients randomized to laser were more likely to achieve target pressure than those on topical therapy 5.

Trabeculectomy should be reserved for:

• Refractory cases not responding to maximum medical therapy 1
• Progressive disease despite treatment
• Patients requiring IOP in the low teens or single digits

Critical Vascular Considerations in NTG

NTG has significant vascular components that distinguish it from high-pressure glaucoma 7, 1:

Screen for and address:

• Nocturnal systemic hypotension (each 10 mmHg lower minimum sleeping systolic BP associated with 0.9 dB worse mean deviation) 8
• Over-treated systemic hypertension 1
• Raynaud's phenomenon and migraine 1
• Consider 24-hour blood pressure monitoring 1
• Systemic calcium channel blockers (nifedipine) may provide additional benefit 1

Important caveat: 40% of NTG patients have systemic hypertension, 53% have blunted nocturnal BP dipping, and 71% have morning BP surge on ambulatory monitoring 8. These vascular factors may be as important as IOP in disease progression.

Monitoring Strategy

Do not rely solely on in-office IOP measurements - maximal daily IOP often occurs outside office hours 9. Consider:

• Multiple baseline IOP measurements at different times of day
• 48-hour IOP profiles when available 10
• Assessment every 6-12 months once stable on treatment

Progression is most commonly detected by visual field testing (36/46 progressions in one study) 10, so prioritize perimetry over structural imaging for monitoring.

Common Pitfalls to Avoid

1. Don't accept "normal" IOP as adequate - the entire premise of NTG is that these patients need lower-than-normal pressures
2. Don't use beta-blockers at bedtime - this can worsen nocturnal hypoperfusion
3. Don't ignore systemic vascular factors - NTG may be part of a systemic small vessel disease spectrum 7
4. Don't assume 20% reduction is sufficient - some patients need IOP in single digits to halt progression 3
5. Don't monitor with structural tests alone - functional changes (visual fields) are more sensitive for detecting NTG progression 10