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Eye pressure is the pressure exerted by the fluid inside the eye against the wall of the eye. Medically, it is known as intraocular pressure and is measured in millimetres of mercury, or mmHg. Values between 10 and 21 mmHg are generally considered normal in healthy individuals. However, this range does not have the same meaning for every person's eye structure and health. Higher values may not cause optic nerve damage in some people, while damage may develop in others even at values considered normal. Eye pressure should therefore be assessed together with examination findings and individual risk factors.
How Is Intraocular Pressure Created?
A fluid called aqueous humour is continuously produced in the front part of the eye. This fluid helps nourish the tissues inside the eye and drains out through specific channels. The balance between fluid production and drainage determines intraocular pressure. Pressure may rise when drainage slows down or fluid circulation is disrupted. In some cases, pressure may fall because of reduced fluid production or fluid loss from the eye. The effects of these changes on eye health vary according to their cause and duration.
What Should Intraocular Pressure Be?
The question of what intraocular pressure should be can generally be answered with a range of 10 to 21 mmHg. These values represent the reference range used for the general population. However, a measurement above 21 mmHg does not necessarily mean that the person has glaucoma. Similarly, a value below 21 mmHg does not mean that the optic nerve is completely safe. For example, it would not be correct to say that values above 18 mmHg are necessarily dangerous in a person with a family history of glaucoma. An appropriate assessment considers the appearance of the optic nerve, the visual field and other examination findings.
Why Can the Normal Value Vary?
Age, family history and the anatomical characteristics of the eye are assessed together when interpreting intraocular pressure. Previous eye operations and medications being used may also affect how the measurement is interpreted. Long-term use of corticosteroid medications may increase intraocular pressure in some people. Pressure values within the normal range may still require close monitoring in people with a vulnerable optic nerve structure. Conversely, the optic nerve may appear healthy despite higher measurements. An individual assessment is therefore required instead of establishing a single normal value for every patient.
Does Corneal Thickness Affect the Measurement?
The cornea is the transparent layer covering the front surface of the eye. Its thickness may cause the eye pressure measurement to appear different from the actual pressure. In people with a thick cornea, the measured value may be higher than the actual pressure. With a thin cornea, the measured value may make the actual pressure appear lower than it is. Corneal thickness is assessed using a method called pachymetry. Interpreting this information together with the optic nerve examination and other tests helps create a more appropriate follow-up plan.
Does Intraocular Pressure Change During the Day?
Intraocular pressure does not remain completely stable throughout the day. In some people, values measured in the morning may be higher than those measured later in the day. The extent of these changes varies between individuals. A single measurement may therefore not reflect all pressure fluctuations. When necessary, measurements at different times or monitoring at specific intervals may be recommended. Monitoring these changes contributes to the assessment process, particularly in people with suspected glaucoma.
Does High Intraocular Pressure Mean Glaucoma?
High intraocular pressure and glaucoma are not the same condition. Glaucoma is a disease associated with optic nerve damage and resulting visual field loss. High intraocular pressure without optic nerve damage is known as ocular hypertension. Not everyone with ocular hypertension develops glaucoma, although the risk may increase over time in some people. Glaucoma may also develop in patients whose intraocular pressure is measured within the normal range. Diagnosis is therefore based not only on pressure measurements but also on optic nerve assessment, visual field testing and the necessary imaging results.
Can Intraocular Pressure Be Low?
Intraocular pressure below the normal range may be temporary in some people. Eye surgery, trauma, inflammation inside the eye or changes in fluid production may cause low pressure. Not every low measurement necessarily indicates a problem requiring treatment. However, a significant fall in pressure or pressure that remains low for an extended period may cause various changes to the structures of the eye. The condition should be assessed without delay if blurred vision, pain or a sudden change in vision occurs. The appropriate approach is determined according to the cause of the low pressure and its effects on the eye.
Does High Intraocular Pressure Cause Symptoms?
High intraocular pressure and chronic glaucoma often cause no symptoms during the early stages. Changes in the optic nerve may therefore have started even though the person believes they can see clearly in daily life. Narrowing of the visual field usually develops gradually and may initially go unnoticed. In some patients, the problem is only identified during a routine examination. In less common cases of sudden pressure elevation, severe eye pain, redness, blurred vision, halos around lights, headache, nausea or vomiting may occur. As these symptoms may be associated with emergencies such as an acute glaucoma attack, they require urgent assessment on the same day.
Who Should Be Monitored More Closely?
Regular monitoring is particularly important for people with a family history of glaucoma. Older age, diabetes, high myopia and long-term corticosteroid use are also among the risk factors considered during assessment. The follow-up plan may also differ for people who have previously experienced eye trauma or undergone eye surgery. Being in a risk group does not necessarily mean that glaucoma will develop. However, regular examinations may help identify changes in the optic nerve at an early stage. The frequency of examinations should be determined according to the person's age, existing findings and risk profile.
How Is Intraocular Pressure Measured?
Intraocular pressure measurement is performed using devices called tonometers. Air-puff devices can measure pressure without touching the ocular surface. Other methods involve applying anaesthetic drops to the ocular surface before taking a contact measurement. Small differences in results may occur depending on the method used during the examination. Squeezing the eyelids, holding the breath or not being sufficiently relaxed may affect the measurement. If the result is uncertain, the measurement may be repeated, and corneal thickness, optic nerve structure and the visual field may also be assessed when necessary.
How Are Treatment and Follow-up Planned?
Not everyone found to have high intraocular pressure needs to begin treatment immediately. The treatment decision is based on whether optic nerve damage is present and the risk of future damage. Eye drops may be used to reduce intraocular pressure when necessary. Laser treatments or surgical methods may be considered in patients for whom eye drops are insufficient or unsuitable. The aim of treatment is to achieve an individual pressure level that helps protect the optic nerve and reduce the risk of existing damage progressing. Using medications regularly and attending follow-up examinations are important parts of the monitoring process. You can contact me using the contact details on my website to arrange an examination appointment.
