Chronic Open-Angle Glaucoma: Target Pressure, Eye Drop Technique and What Protects Sight
The eye continuously produces a clear fluid, aqueous humour, which nourishes the front of the eye and then drains out through a mesh of tissue at the angle between iris and cornea. In chronic open-angle glaucoma that angle stays open, but the mesh drains too slowly. Pressure inside the eye rises, and the optic nerve fibres carrying vision to the brain are gradually lost.
Two features make this disease what it is. The first is that it is painless and invisible: the brain fills in the missing areas of peripheral vision so convincingly that people commonly lose half their visual field without noticing. The second is that the damage is permanent. Nerve fibres do not regenerate.
What can be changed is the rate. Lowering pressure slows or halts further loss, and it is currently the only proven way to do so. Everything in the treatment of glaucoma follows from that single sentence.
📊 The target is a percentage, not a number
Normal intraocular pressure runs from about 10 to 21 mmHg, but that range is a population statistic rather than a treatment goal. Around a third of people with glaucoma damage have pressures inside the normal range, a form called normal-tension glaucoma. Others have pressures of 24 mmHg for decades and never lose a nerve fibre.
🎯 How target pressure is set. The ophthalmologist takes the untreated baseline and aims to bring it down by 20 to 30 percent, further in advanced disease or where damage is progressing. A landmark trial in people with raised pressure but no damage showed that a 20 percent reduction roughly halved the rate of developing glaucoma. The target is then revised according to whether scans and visual fields stay stable.
Because pressure fluctuates through the day and one reading at 11 am says little, and because corneal thickness distorts the measurement, diagnosis and monitoring rest on several tests together:
| Test | What it shows |
|---|---|
| Tonometry | The pressure itself, at that moment |
| Pachymetry | Corneal thickness. A thin cornea under-reads pressure and is itself a risk factor |
| Gonioscopy | Whether the drainage angle is open or closed, which separates two different diseases |
| Optic disc examination | Cupping, the hollowing of the nerve head as fibres are lost |
| OCT imaging | Nerve fibre layer thickness, which detects loss years before the visual field does |
| Visual field testing | Function. Progression is judged on repeated fields over time, not one result |
🚦 Who should be tested, and when
- 👨👩👧 A parent or sibling with glaucoma — raises risk severalfold and is the strongest single factor after age
- 🎂 Age over 40, with risk climbing steadily each decade
- 🌍 African or Caribbean ancestry — earlier onset and faster progression, so screening starts younger
- 👁️ Short-sightedness, particularly high myopia
- 💉 Long-term corticosteroids in any form, including inhalers, nasal sprays and creams, and especially steroid eye drops
- 🩸 Diabetes, and low blood pressure at night, which reduces perfusion of the nerve head
- 💥 Previous eye injury or surgery
For anyone in these groups the interval is usually every one to two years. Waiting for symptoms is not a strategy, because symptoms mean a substantial proportion of the nerve has already gone.
💧 Eye drops: the classes and what each does
Drops either reduce the production of aqueous humour or increase its outflow. Most people start on one and add a second if the target is not reached.
| Class | Examples | Effect on pressure | Main issue |
|---|---|---|---|
| Prostaglandin analogues | Latanoprost, bimatoprost, travoprost | 25 to 33 percent, the strongest single class | Cosmetic changes to the eye and lashes |
| Beta-blockers | Timolol | 20 to 25 percent | Systemic absorption: bronchospasm, slow pulse |
| Carbonic anhydrase inhibitors | Dorzolamide, brinzolamide | 15 to 20 percent | Stinging, bitter taste |
| Alpha agonists | Brimonidine | 20 to 25 percent | Allergic reactions with long use; avoided in young children |
| Rho kinase inhibitors | Netarsudil | Around 20 percent | Redness, small corneal deposits |
Of these, we stock the first-line option: Xalatan (Latanoprost), in the eye drops category.
⚠️ Timolol drops are a real beta-blocker. Enough is absorbed through the nasal mucosa to affect the whole body. They can trigger severe bronchospasm in asthma, slow the heart, worsen heart failure and mask the warning signs of low blood sugar in diabetes. Anyone with asthma, COPD or a slow heart rate should make sure the eye clinic knows before beta-blocker drops are prescribed.
🔬 Latanoprost in practice
Latanoprost increases outflow through an alternative drainage route at the base of the iris. It lowers pressure more than any other single drop and needs applying only once a day, which is why it became the standard first choice.
- 🌙 One drop in the affected eye, once daily, in the evening. Evening dosing works better than morning
- 🚫 More than once daily reduces the effect, which is counterintuitive and true. Doubling up after a missed dose is not helpful
- 🧊 Store the unopened bottle in the fridge. Once opened it keeps at room temperature for four weeks, then is discarded even if liquid remains
- 📅 Full effect takes three to five weeks, so pressure is rechecked rather than judged early
👁️ The cosmetic effects, which should be disclosed before starting
- Permanent darkening of the iris
- Increased brown pigment, developing over months and irreversible. It is most noticeable in mixed-colour eyes such as green-brown or blue-brown, and in someone treated in one eye only it can leave the two eyes visibly different colours. It is harmless but it does not go away.
- Longer, thicker, darker eyelashes
- Reversible on stopping. The same molecule family is sold cosmetically for exactly this effect.
- Darkening of the eyelid skin
- Usually reversible.
- Hollowing around the eye
- Loss of orbital fat gives a sunken appearance with long use, and it partially reverses after stopping.
- Redness of the eye
- Common early and usually settles.
👌 The technique that decides whether the drop works
Studies observing patients putting in their own drops find that a large proportion miss the eye entirely, touch the bottle to the eye, or use several drops per dose. All three undermine treatment.
- Wash hands. Tilt the head back, or lie down
- Pull the lower lid down to make a pocket, and look up
- Squeeze one drop into the pocket, never onto the cornea directly, and do not let the tip touch the eye or lashes
- Close the eye gently for two minutes. Do not squeeze or blink hard, which pumps the drop away
- Press the inner corner of the eye, where the tear duct is, for one to two minutes
- If a second different drop is due, wait five minutes, otherwise the second washes out the first
💡 Why step 5 matters twice over. The eye holds about 30 microlitres and a drop is around 50, so a second drop only runs down the cheek. What does not stay in the eye drains through the tear duct into the nose, where it is absorbed into the bloodstream directly, bypassing the liver. Pressing the tear duct closed keeps more drug on the eye and cuts systemic absorption substantially. With beta-blocker drops that is a safety measure, not a refinement.
One further practical point: most glaucoma drops contain benzalkonium chloride as preservative, which irritates the ocular surface and causes dry, gritty, red eyes over years of use. Preservative-free formulations exist for people on multiple drops long term, and are worth asking about when the eyes become uncomfortable.
⚡ Laser, and where it now sits
Selective laser trabeculoplasty applies short low-energy pulses to the drainage mesh, stimulating it to work better. It is an outpatient procedure taking a few minutes, with no incision.
Its status changed after a large randomised trial compared laser first against drops first in newly diagnosed patients. Laser-first patients were more likely to be at target pressure, more likely to be off drops entirely, and needed less surgery. Many ophthalmologists now offer it as a first-line alternative rather than a fallback. The effect wears off over three to five years, and the procedure can be repeated.
Where laser and drops are insufficient, surgical options run from minimally invasive stents through to trabeculectomy, which creates a new drainage channel and lowers pressure the most.
💊 Acetazolamide: short-term, not long-term
Diamox (Acetazolamide 125/250/500 mg) is a carbonic anhydrase inhibitor taken by mouth, which cuts aqueous production substantially and lowers pressure fast.
Its place is specific: acute pressure spikes, acute angle-closure before laser treatment, and preparation for surgery. It is not used as ongoing treatment for chronic open-angle glaucoma, because systemic side effects accumulate: tingling in the fingers and toes, fatigue, a strange metallic taste that makes carbonated drinks taste unpleasant, loss of appetite, low potassium, kidney stones and metabolic acidosis. It is avoided in sulfonamide allergy, in significant kidney or liver disease, and in low potassium.
🚨 The glaucoma that is an emergency
🚑 Acute angle-closure glaucoma is a different disease and needs care within hours. The drainage angle closes suddenly, pressure rises to extreme levels, and untreated it destroys sight within a day or two. The presentation is unmistakable: severe eye pain and headache, a red eye, blurred vision with halos around lights, nausea and vomiting, and a mid-sized pupil that does not react. The vomiting frequently sends people to a general emergency department where the eye is overlooked. Anyone with these symptoms needs an eye assessment immediately.
It is worth knowing that several common medicines can precipitate an attack in an anatomically predisposed eye: anticholinergics, some antidepressants and antihistamines, and drugs used for bladder problems. Their packaging warnings about glaucoma refer to this form, not to open-angle glaucoma, which is why people on latanoprost are often needlessly alarmed by them.
🏃 What lifestyle can and cannot do
- ✅ Regular aerobic exercise lowers intraocular pressure modestly and is worth doing
- ❌ Head-down yoga inversions raise pressure sharply for as long as they are held, and are best avoided
- 🎺 High-resistance wind instruments and heavy straining with a held breath cause pressure spikes
- 👕 Tight neckties and tight collars raise measured pressure; loosen before a reading
- ☕ Large amounts of caffeine at once raise pressure briefly. Ordinary consumption is not a problem
- 🛏️ Sleeping with the head slightly raised reduces night-time pressure a little
- 🚬 Stopping smoking and controlling blood pressure and diabetes support perfusion of the optic nerve
- 🌊 No diet or supplement has been shown to stop glaucoma progression
❓ Frequently asked questions
Can vision lost to glaucoma come back?
No. Optic nerve fibres do not regenerate, so lost visual field is permanent. Treatment protects what remains, which is why detection before symptoms appear matters so much.
What eye pressure is considered safe?
There is no universal number. The target is set as a 20 to 30 percent reduction from the untreated baseline, lower in advanced disease. About a third of people with glaucoma damage have pressures within the normal range.
How do I use latanoprost drops?
One drop in the affected eye once daily in the evening. Using it more often actually reduces its effect. Store the unopened bottle in the fridge, and discard it four weeks after opening. Full effect takes three to five weeks.
Will latanoprost change my eye colour?
It can, and the change is permanent. Increased brown pigment develops over months, most noticeably in mixed-colour eyes such as green-brown or blue-brown. Longer darker eyelashes and eyelid darkening also occur but reverse after stopping.
Why press on the corner of my eye after drops?
Because what drains through the tear duct into the nose is absorbed straight into the bloodstream. Pressing the inner corner for one to two minutes keeps more drug on the eye and reduces whole-body absorption, which matters most with beta-blocker drops.
Do I need to wait between two different eye drops?
Yes, at least five minutes. Applied immediately after each other, the second simply washes the first out of the eye.
Can eye drops affect the rest of my body?
Beta-blocker drops such as timolol can. Enough is absorbed to cause bronchospasm in asthma, slow the heart and mask low blood sugar. Tell the eye clinic about asthma, COPD, heart conditions or a slow pulse before starting them.
Is laser treatment better than drops?
In a large randomised trial, patients given selective laser trabeculoplasty first were more likely to reach target pressure and to remain free of drops, and needed less surgery. Many ophthalmologists now offer it as a first-line option. The effect fades over three to five years and can be repeated.
Which glaucoma symptoms are an emergency?
Severe eye pain with headache, a red eye, blurred vision with halos around lights, nausea and vomiting. That is acute angle-closure glaucoma, a different condition that destroys sight within a day or two without treatment.
Can diet or supplements slow glaucoma?
No supplement or diet has been shown to stop progression. Regular aerobic exercise lowers pressure modestly, while head-down yoga inversions and heavy straining raise it sharply and are best avoided.
📑 Sources and editorial
- Ophthalmology guidelines on the diagnosis and management of chronic open-angle glaucoma and ocular hypertension
- The Ocular Hypertension Treatment Study on pressure reduction and conversion to glaucoma
- The LiGHT randomised trial comparing selective laser trabeculoplasty with eye drops as initial treatment
- Prescribing information for latanoprost, timolol and acetazolamide, including iris pigmentation and systemic beta-blocker effects
- Studies of eye drop instillation technique, nasolacrimal occlusion and benzalkonium chloride toxicity to the ocular surface
- Related reading: chronic obstructive pulmonary disease
- Related products: Xalatan (Latanoprost), Diamox (Acetazolamide), eye drops category
- RXshop Editorial Team — reviewed by Sarah Mitchell, PharmD — Clinical Pharmacist & Chief Editorial
Medical Disclaimer: The information in this article is for educational and informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek guidance from a qualified healthcare provider with any questions you may have regarding a medical condition, and before starting, stopping or changing any medication.