Understanding Eye Pressure: Why IOP Changes Throughout the Day

Your circadian rhythm, your body's internal 24-hour clock, influences how much fluid your eye produces and drains at different times. This cycle affects hormone levels, blood flow, and other processes that shift your IOP even when your activity level stays the same. Aqueous humor production typically slows at night, but drainage can also decrease during sleep, which often causes pressure to rise.

Lying down raises the pressure inside your eye compared to sitting or standing. When you are flat, more blood flows to your head and eyes, and fluid does not drain as easily from the eye. This is why many people experience their highest pressure during sleep. The effect is most clinically significant in people whose glaucoma continues to worsen despite apparently controlled pressures during office visits.

• Sitting upright typically produces the lowest pressure readings
• Lying flat can raise IOP by 2 to 6 mmHg or more
• Face-down sleeping positions may increase pressure further
• The eye resting against a pillow may experience transiently higher pressure in some people

Most forms of aerobic exercise, such as walking, running, or cycling, temporarily lower eye pressure during and shortly after the activity by improving fluid drainage. Regular physical activity may also help keep pressure more stable over time.

Certain activities, however, can raise IOP briefly. Weightlifting, playing wind instruments, or performing inverted yoga poses can cause short-term spikes. Straining or holding your breath during exercise also increases pressure. We may recommend modifying specific activities if you have poorly controlled glaucoma or very high IOP.

Drinking a large volume of fluid quickly can cause a temporary rise in eye pressure as your body processes the extra water. Spreading fluid intake throughout the day helps avoid sudden spikes. We do not generally recommend restricting total daily hydration; the goal is simply to avoid rapid large-volume intake if you are sensitive to these spikes.

Caffeine can cause small, temporary pressure increases in some individuals. A diet rich in fruits, vegetables, and omega-3 fatty acids supports overall eye health and may contribute to better pressure control. We recommend a balanced diet as part of your complete eye care plan.

Many prescription and over-the-counter medications can influence your eye pressure. Corticosteroids in any form, including pills, inhalers, skin creams, and eye drops, may raise IOP significantly in susceptible people, sometimes within weeks of starting the medication. Always share a complete list of your medications, supplements, and herbal products with us.

• 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 a dangerous pressure spike in people with narrow angles
• Decongestants, certain antihistamines, and some antidepressants fall into this category
• Prescription glaucoma eye drops lower pressure when used correctly and consistently

If you have been told you have narrow drainage angles, ask us before starting any new dilating or anticholinergic medication.

Hormones affect fluid balance throughout the body, including the eyes. Some people notice pressure changes related to their menstrual cycle, pregnancy, or menopause. Thyroid disorders can also impact IOP, and we take these factors into account when reviewing your pressure patterns.

Some evidence suggests eye pressure may shift slightly with the seasons, possibly due to changes in daylight exposure, temperature, or activity habits. These variations are usually small, but they reinforce the value of tracking your pressure over many months and years to build a complete picture of your eye health.

We recommend treatment when pressure fluctuations or sustained elevations pose a meaningful risk to your optic nerve. This applies when IOP swings widely throughout the day, peaks very high at certain times, or stays above normal ranges consistently. People who already have glaucoma damage need treatment to prevent further vision loss, and those at high risk may benefit from starting therapy before damage occurs.

Your family history, optic nerve appearance, visual field results, and corneal thickness all factor into our decision. The goal is to keep your IOP both low and stable around the clock, not just during office visits.

Eye drops are the most common first treatment for high or unstable eye pressure. Different classes of drops work in different ways, with some reducing how much fluid the eye produces and others improving how well fluid drains. We typically start with one drop and add others if needed to reach your target pressure.

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

Selective laser trabeculoplasty, or SLT, uses gentle laser energy to improve fluid drainage through the trabecular meshwork, which is the eye's primary drainage system. This quick in-office procedure can reduce IOP by roughly 20 to 30 percent in people who respond to it, and it may reduce the need for daily eye drops, though results vary.

SLT can be used as a first-line option or added to an existing eye drop regimen. Its effects typically last several years, and the procedure can be safely repeated if pressure rises again over time. A temporary short-term pressure spike or mild inflammation can occur after treatment, so we check your IOP following the procedure. Some patients still need drops after SLT, but often fewer medications at lower doses.

When drops and laser treatment are not enough to control your pressure adequately, surgery may be the next step. Traditional trabeculectomy creates a new drainage outlet under the eyelid to allow fluid to filter out of the eye. For advanced glaucoma that needs to reach very low target pressures, this approach or a tube shunt device may be necessary.

Minimally invasive glaucoma surgery, or MIGS, offers a gentler class of options with faster recovery and lower risk profiles. MIGS procedures work through tiny incisions and include microscopic stents that open drainage channels, devices that redirect fluid to new areas, or techniques that enhance natural outflow. MIGS is generally well-suited to mild or moderate glaucoma and is frequently performed at the same time as cataract surgery. We recommend the right surgical approach based on the severity of your condition and how your eye has responded to other treatments.

Healthy daily habits can complement medical treatment and support more consistent pressure control. These changes benefit your overall wellbeing while also contributing to your eye health.

• Aim for 30 minutes of moderate aerobic exercise most days of the week
• Spread fluid intake throughout the day rather than consuming large amounts at once
• Elevate your head slightly during sleep if nighttime pressure spikes are a concern
• Limit caffeine if you notice it affects your pressure readings
• Take prescribed eye drops at the same times each day for the most consistent effect

Regular follow-up appointments allow us to track how well your treatment is controlling pressure fluctuations and protecting your optic nerve. How often you return depends on the severity of your condition and how stable your pressure has been. People with high-risk or poorly controlled IOP may need visits every few weeks or months.

At each visit, we measure your pressure, examine your optic nerve, and may perform visual field testing to check for any changes. Once pressure is stable and well controlled, we may extend intervals to every three to six months. Lifelong monitoring remains essential because both eye pressure and glaucoma can change over time even when treatment has been going well.