Understanding Eye Pressure: Why IOP Fluctuates and What It Means for You

Your body's internal clock, called the circadian rhythm, influences how much fluid your eye produces and drains at different times. Aqueous humor production typically slows during sleep, but drainage can also decrease when you are lying down, which often causes pressure to rise overnight. This is one reason why a single daytime reading may not reveal your true pressure peaks.

Lying flat increases eye pressure compared to sitting or standing. When you are horizontal, more blood flows toward your head and eyes, and fluid inside your eye does not drain as easily. This positional effect is most clinically important when glaucoma is worsening despite pressures that appear controlled in the office.

• Sitting upright generally produces the lowest pressure readings
• Lying flat can raise IOP by 2 to 6 mmHg or more
• Face-down positions may increase pressure even further
• The side you sleep on may transiently raise pressure in the lower eye

Most aerobic exercise, such as walking, running, or cycling, temporarily lowers IOP during and after activity by improving fluid drainage. Regular physical activity may help keep your pressure more stable over time. However, certain activities can cause short-term spikes, including heavy weightlifting, playing wind instruments, headstands, or any activity that involves straining or holding your breath. We may recommend modifying certain exercises if your glaucoma is not well controlled.

Drinking a large volume of fluid very quickly can cause a temporary rise in eye pressure. Spreading your fluid intake throughout the day helps avoid these sudden spikes. We do not recommend restricting your total daily hydration, only avoiding rapid large-volume intake if you are sensitive to pressure increases.

Caffeine can cause small, temporary IOP increases in some people, typically lasting about 90 minutes. A diet rich in fruits, vegetables, and omega-3 fatty acids supports overall eye health, and we recommend a balanced diet as part of your care plan.

Many prescription and over-the-counter medications affect eye pressure. Corticosteroids taken in any form, including pills, inhalers, skin creams, or eye drops, can raise IOP significantly in susceptible individuals, sometimes within weeks of starting treatment. Always tell your eye care provider about every medication, supplement, and herbal product you use.

• Corticosteroids in any form can increase eye pressure
• Some blood pressure medications may influence IOP
• Medications that dilate the pupil or have anticholinergic effects can trigger acute angle closure in people with narrow angles
• Decongestants, some antihistamines, and certain antidepressants are examples where your angle anatomy matters
• Prescription glaucoma eye drops lower pressure when used correctly and consistently

If you have been told you have narrow angles, ask your provider before starting any new dilating or anticholinergic medications.

Hormones affect fluid balance throughout the body, including the eyes. Women may notice pressure changes related to their menstrual cycle, pregnancy, or menopause. Thyroid conditions can also impact IOP. Some evidence suggests eye pressure may vary slightly with the seasons, possibly due to changes in temperature, daylight, or activity. These variations are usually small, but they remind us that tracking pressure over months and years gives the most complete picture of your eye health.

We recommend treatment when IOP swings widely, peaks very high at certain times, or remains consistently elevated beyond a safe range. People with existing glaucoma damage need treatment to prevent further vision loss, while those at high risk may benefit from starting therapy before any damage occurs. Your family history, optic nerve appearance, corneal thickness, and other individual risk factors all guide our decision.

Eye drops are the most common first-line treatment for high or unstable eye pressure. Different medication classes work in different ways, with some reducing how much fluid your eye produces and others improving drainage. We often start with one drop and add others as needed to reach your target pressure range.

• Prostaglandin analogs are usually the first choice and provide strong 24-hour pressure control
• Beta-blockers reduce fluid production and are typically used twice daily
• Alpha agonists lower pressure and are often added to other drops
• Carbonic anhydrase inhibitors decrease fluid production through a different mechanism
• Combination drops contain two medications in a single bottle for added convenience

A procedure called selective laser trabeculoplasty, or SLT, uses gentle laser energy to improve fluid drainage through the trabecular meshwork, which is the eye's main drainage channel. This short, in-office procedure can reduce the need for daily eye drops, though individual response varies. SLT lowers pressure by approximately 20 to 30 percent in those who respond, and the effects can last several years. The procedure can be safely repeated if pressure rises again over time. Temporary inflammation or a brief pressure spike can occur after SLT, so we check your IOP following treatment.

When eye drops and laser treatment do not provide adequate control, surgery may be necessary. Traditional trabeculectomy creates a new drainage channel under the eyelid, allowing fluid to filter out of the eye and dramatically lower IOP. This approach is typically reserved for more advanced disease.

Minimally invasive glaucoma surgeries, known as MIGS, offer gentler alternatives with faster recovery times and lower risk profiles than traditional surgery. MIGS options include tiny stents that hold drainage channels open and devices that shunt fluid to new areas within the eye. These procedures are often performed alongside cataract surgery and are best suited for mild-to-moderate glaucoma. For advanced disease, tube shunts or trabeculectomy remain the standard for reaching very low target pressures. We recommend surgery based on your degree of glaucoma and how well other treatments have performed.

Daily habits can support more stable eye pressure alongside medical treatment. Regular aerobic exercise, a healthy weight, and stress management all contribute to better pressure control and benefit your overall health at the same time.

• Aim for moderate aerobic exercise for about 30 minutes most days
• Spread your fluid intake throughout the day to avoid sudden pressure spikes
• Consider slightly elevating your head during sleep if you have nighttime pressure concerns
• Limit caffeine if you notice it affects your IOP
• Take prescribed eye drops at the same times each day to maintain consistent pressure control

Regular follow-up visits allow us to track how well treatment is controlling your pressure and protecting your optic nerve. Visit frequency depends on how severe your condition is and how stable your pressure has become. People with high-risk or poorly controlled IOP may need checks every few weeks, while stable, well-controlled cases may only need visits every three to six months.

At each follow-up, we measure your pressure, examine your optic nerve, and may perform visual field tests to look for any changes. We adjust your medications or recommend additional treatments based on what we find. Lifelong monitoring is essential because eye pressure and glaucoma can change over the years.