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How Accurate Is Your Eye Pressure Test? A Patient’s Guide to IOP Measurement Methods · Glaucoma, Vision & Longevity: Supplements & Science

• 0:00
  SPEAKER_00: How accurate is your eye pressure test?
• 0:02
  SPEAKER_00: A patient's guide to IOP measurement methods.
• 0:06
  SPEAKER_00: Was your test a puff of air, a blue light, and a small tip touching your eye, or a tiny probe tapping your cornea?
• 0:13
  SPEAKER_00: Each is a way to estimate intraocular pressure, IOP, the fluid pressure inside the eye.
• 0:19
  SPEAKER_00: The tests may give different numbers, even when they are done minutes apart.
• 0:23
  SPEAKER_00: That does not automatically mean one test was wrong.
• 0:25
  SPEAKER_00: They use different methods, and each is affected by the eye's surface, the testing technique, and ordinary changes in pressure over time.
• 0:34
  SPEAKER_00: This guide explains how to recognize the main tests, what their readings can and cannot tell you, and when another measurement might help.
• 0:42
  SPEAKER_00: The short version Goldman Aplanation Tonometry is the usual clinical reference, not a perfect reading of true pressure.
• 0:50
  SPEAKER_00: A number is most useful when interpreted alongside your cornea, optic nerve, visual field, and previous readings.
• 0:57
  SPEAKER_00: First, what does accurate mean?
• 0:59
  SPEAKER_00: A tonometer does not usually place a sensor inside the eye.
• 1:03
  SPEAKER_00: Most estimate pressure by observing how the cornea, the clear front window of the eye, responds to air or gentle contact.
• 1:10
  SPEAKER_00: The cornea's thickness, shape, stiffness, hydration, and surface can affect that estimate.
• 1:16
  SPEAKER_00: It helps to distinguish two ideas.
• 1:18
  SPEAKER_00: Agreement asks whether a method gives a similar number to a reference method.
• 1:23
  SPEAKER_00: Repeatability asks whether the method gives similar numbers when the test is repeated.
• 1:28
  SPEAKER_00: A device can be repeatable yet consistently read a little high or low.
• 1:33
  SPEAKER_00: And two devices can have almost the same average result across a group of people while disagreeing by several millimeters of mercury gram in a particular person.
• 1:43
  SPEAKER_00: How to read the scores in this guide.
• 1:45
  SPEAKER_00: The 1 to 100 ratings below are editorial comparison scores, not percentages, validated medical scores, or an official ranking.
• 1:54
  SPEAKER_00: They are broad estimates of how useful a method is for matching established clinical measurements in a trained, untreated adult with a structurally typical cornea.
• 2:04
  SPEAKER_00: The assessment considers agreement with Goldman applination tonometry and, where available, direct pressure measurements, systematic bias, repeatability, and how well the method holds up across pressure levels and patient characteristics.
• 2:19
  SPEAKER_00: A score of 90 does not mean 90% correct.
• 2:23
  SPEAKER_00: A few points difference is not meaningful proof that one device is better for an individual.
• 2:28
  SPEAKER_00: Evidence confidence labels describe how confident we are in the comparison, not whether a reading from that device is guaranteed to be right.
• 2:37
  SPEAKER_00: When studies report 95% limits of agreement, those limits describe the range in which about 95% of individual paired differences between two methods fell in that study or pooled analysis.
• 2:50
  SPEAKER_00: They are more informative about person-to-person differences than an average difference alone, but they still do not say which method was closer to the true pressure.
• 2:59
  SPEAKER_00: At a glance, how the methods compare.
• 3:03
  SPEAKER_00: For the full table, please open this article on visualfieldtest.com.
• 3:07
  SPEAKER_00: The comparison evidence is not a clean contest between identical devices.
• 3:11
  SPEAKER_00: Studies differ in patient groups, instrument models, pressure ranges, and testing procedures.
• 3:17
  SPEAKER_00: In a large systematic review, agreement with Goldman varied substantially among methods.
• 3:22
  SPEAKER_00: For example, pooled 95% limits of agreement were roughly minus 4 to plus 4 millimeter hergrangs for some non-contact tests and wider for several other devices.
• 3:32
  SPEAKER_00: The review also found notable differences between studies and between repeated measurements.
• 3:37
  SPEAKER_00: Systematic review of tonometer agreement.
• 3:40
  SPEAKER_00: Why Goldman is the clinical reference, but not a perfect truth.
• 3:45
  SPEAKER_00: Goldman Applanation Tonometry, the blue light test.
• 3:48
  SPEAKER_00: How it works, a clinician looks through a slit lamp, a microscope used during an eye examination, and uses a small prism to flatten a tiny area of the cornea.
• 3:58
  SPEAKER_00: The instrument estimates pressure from the force needed to flatten it.
• 4:02
  SPEAKER_00: What it feels like.
• 4:03
  SPEAKER_00: Numbing drops are usually used along with fluorescence dye, which makes the contact point visible under blue light.
• 4:10
  SPEAKER_00: The prism briefly touches the cornea.
• 4:12
  SPEAKER_00: The procedure usually takes only a short time for each eye.
• 4:16
  SPEAKER_00: You may feel the drops or notice the light, but the eye should not feel sharp pain.
• 4:21
  SPEAKER_00: Where it is used.
• 4:22
  SPEAKER_00: Goldman is a major reference method in glaucoma care.
• 4:26
  SPEAKER_00: For example, the United Kingdom's National Institute for Health and Care Excellence recommends Goldman type applination tonometry in glaucoma assessment and says referral decisions should not be based solely on a non-contact reading.
• 4:40
  SPEAKER_00: National Institute for Health and Care Excellence Glaucoma Recommendations.
• 4:45
  SPEAKER_00: Wyatt is trusted.
• 4:47
  SPEAKER_00: Clinicians have extensive experience with it, the technique is well established, and many studies and clinical decisions use it as the comparison standard.
• 4:57
  SPEAKER_00: Keeping to the same method over time can make it especially helpful for tracking change.
• 5:02
  SPEAKER_00: Wyatt is not a direct measurement of true pressure.
• 5:05
  SPEAKER_00: Goldman estimates pressure through the cornea.
• 5:08
  SPEAKER_00: Its original design assumes average corneal properties.
• 5:12
  SPEAKER_00: Differences in thickness and biomechanics can therefore change the reading.
• 5:17
  SPEAKER_00: It is commonly used as the clinical reference because it is established and practical, not because it directly measures fluid pressure inside the eye.
• 5:26
  SPEAKER_00: A true direct measurement requires placing a pressure sensor or cannula inside the eye, something generally limited to research or an operation.
• 5:35
  SPEAKER_00: In a small human cadaver eye study, Pascal dynamic contour readings were closer to experimentally set intracameral pressure than Goldman readings.
• 5:43
  SPEAKER_00: Cadaver eyes, however, are not the same as living eyes in routine practice.
• 5:48
  SPEAKER_00: Intracameral monometry comparison, Perkins handheld applination tonometry.
• 5:54
  SPEAKER_00: How it works.
• 5:55
  SPEAKER_00: The Perkins instrument uses the same basic applination principle as Goldman, but is handheld rather than mounted on a slit lamp.
• 6:03
  SPEAKER_00: What it feels like, it usually requires numbing drops and fluorescine dye, and the instrument briefly touches the cornea.
• 6:11
  SPEAKER_00: It can be used with a patient sitting or lying down, depending on the situation.
• 6:16
  SPEAKER_00: Where it is used, its portability can be useful in hospitals for patients who cannot sit at a slit lamp and when pressure must be checked with someone lying down.
• 6:25
  SPEAKER_00: It is also used in some children and in people under anesthesia.
• 6:29
  SPEAKER_00: It has a similar underlying measurement approach to Goldman, but a handheld test still depends on careful positioning and technique.
• 6:37
  SPEAKER_00: American Academy of Ophthalmology Assessment of Rebound Tonometry in Children.
• 6:42
  SPEAKER_00: Air puff or non-contact tonometry.
• 6:45
  SPEAKER_00: How it works, a machine sends a quick puff of air toward the cornea and detects how the cornea responds.
• 6:51
  SPEAKER_00: There is no instrument touching the eye.
• 6:54
  SPEAKER_00: What it feels like, you rest your chin and forehead on the machine and look at a target.
• 6:59
  SPEAKER_00: The puff can be startling, but it is over quickly.
• 7:03
  SPEAKER_00: Numbing drops and fluorescine are not needed.
• 7:06
  SPEAKER_00: Where it is used, it is often used for routine screening because it is quick and does not require corneal contact.
• 7:13
  SPEAKER_00: The exact mix of devices in community eye care settings varies.
• 7:17
  SPEAKER_00: Reliable country by country comparisons of how widely each type of tenometer is used are lacking, so a device's availability in a country should not be taken as evidence that it dominates there.
• 7:29
  SPEAKER_00: How to interpret it?
• 7:30
  SPEAKER_00: A systematic review found that pooled airpuff results were among the methods that most closely matched Goldman on average.
• 7:38
  SPEAKER_00: But studies still showed individual differences of several memony her grams, and the result can be affected by the cornea and by device design.
• 7:45
  SPEAKER_00: Airpuff testing is useful, but a concerning reading may need confirmation with an applination test or another suitable method.
• 7:53
  SPEAKER_00: Systematic review of tonometer agreement, rebound tonometry, the tiny probe test.
• 7:59
  SPEAKER_00: How it works.
• 8:00
  SPEAKER_00: A handheld device briefly propels a very light, disposable probe toward the cornea.
• 8:05
  SPEAKER_00: The device measures how the probe slows and rebounds.
• 8:08
  SPEAKER_00: A clinic-based eye care session typically takes several readings and combines them.
• 8:14
  SPEAKER_00: What it feels like, you may hear a quiet click or feel a light tap.
• 8:18
  SPEAKER_00: Topical anesthetic drops are usually not needed.
• 8:21
  SPEAKER_00: Where it is used, clinic-based rebound devices can be useful for children, bedside assessments, and people who find a slit lamp difficult.
• 8:30
  SPEAKER_00: Models differ.
• 8:31
  SPEAKER_00: A model designed for a trained clinician should not be assumed to work the same way as a model designed for self-testing.
• 8:38
  SPEAKER_00: American Academy of Ophthalmology reviewers found that children's readings from rebound telonometry were often 2 to 3 mm higher than Goldman readings in the small number of comparable studies they reviewed.
• 8:50
  SPEAKER_00: That does not mean every rebound reading should be reduced by 2 to 3 mmHg, it means the methods can differ.
• 8:58
  SPEAKER_00: American Academy of Ophthalmology assessment of rebound tonometry in children.
• 9:03
  SPEAKER_00: Eye care home and home 2.
• 9:05
  SPEAKER_00: Home pressure checks.
• 9:06
  SPEAKER_00: Eye care home devices use rebound telometry, but are designed for eligible patients to measure their own pressure after instruction.
• 9:14
  SPEAKER_00: Home measurement is a way to collect more readings at different times.
• 9:18
  SPEAKER_00: Not a reason to treat each individual number as exact.
• 9:22
  SPEAKER_00: A systematic review and meta-analysis published in 2026 found little average difference between eye care home and goldman readings, but the spread between individual paired readings remains substantial.
• 9:35
  SPEAKER_00: Estimated limits were about plus 5 millimeter hergrams.
• 9:39
  SPEAKER_00: The review rated the evidence very low certainty, partly because study results varied.
• 9:44
  SPEAKER_00: So a close average across studies does not mean that a particular person's home and clinic numbers will always match.
• 9:51
  SPEAKER_00: 2026 Systematic Review of Eye Care Home and Goldman Agreement.
• 9:55
  SPEAKER_00: What home monitoring can add, a clinic reading is a snapshot.
• 9:59
  SPEAKER_00: With advice from your eye care professional, home readings at different times may show whether your pressure rises or falls at particular times of day.
• 10:08
  SPEAKER_00: They may help a clinician decide whether further testing at another time is useful.
• 10:13
  SPEAKER_00: What it cannot do, it does not continuously track pressure, diagnose glaucoma, or reliably replace an office examination.
• 10:22
  SPEAKER_00: Home and clinic readings are best compared by checking the device against a clinic measurement, ideally with the patient and clinician measuring around the same visit.
• 10:31
  SPEAKER_00: A clinician can then interpret a pattern in context.
• 10:34
  SPEAKER_00: Do not change drops, delay care, or make a treatment decision based on a home device score or one isolated reading.
• 10:43
  SPEAKER_00: Tono pen and related handheld applination devices.
• 10:46
  SPEAKER_00: How it works.
• 10:47
  SPEAKER_00: The tono pen is a small handheld instrument with a narrow tip that briefly touches the cornea.
• 10:52
  SPEAKER_00: It estimates pressure using a small contact area and averages multiple touches.
• 10:58
  SPEAKER_00: What it feels like.
• 10:59
  SPEAKER_00: The cornea is usually numbed first.
• 11:01
  SPEAKER_00: You may feel a light touch rather than an air puff.
• 11:05
  SPEAKER_00: Testing is brief.
• 11:06
  SPEAKER_00: Where it is used, its portability and small contact area can be useful at the bedside, in emergency care for patients who cannot sit at a slit lamp and when part of the cornea is scarred or irregular.
• 11:17
  SPEAKER_00: It may allow a measurement where a larger applanation area is difficult to use, but a small tip does not make every corneal condition easy to measure.
• 11:26
  SPEAKER_00: A caution.
• 11:28
  SPEAKER_00: Results are not always close enough to Goldman to swap freely.
• 11:32
  SPEAKER_00: In one clinical comparison, tonopen readings tended to be higher at very low pressure and lower at pressures at or above 30 mmHg.
• 11:40
  SPEAKER_00: The exact pattern can depend on the study and device.
• 11:44
  SPEAKER_00: Clinical comparison of tonometers in different pressure ranges.
• 11:50
  SPEAKER_00: How it works.
• 11:52
  SPEAKER_00: A slit lamp mounted sensor tip is shaped to fit the normal contour of the cornea.
• 11:56
  SPEAKER_00: Rather than flattening a standard area in the same way as Goldman, it measures pressure at the tip.
• 12:02
  SPEAKER_00: What it feels like.
• 12:04
  SPEAKER_00: The device touches the numbed cornea.
• 12:06
  SPEAKER_00: The contact can last several seconds, longer than the brief Goldman touch, and the clinician needs a steady position.
• 12:13
  SPEAKER_00: Where it is used, it is an alternative used in some specialist and glaucoma clinics.
• 12:18
  SPEAKER_00: Research suggests it may be less affected by corneal thickness than Goldman in some groups.
• 12:24
  SPEAKER_00: However, studies comparing it with Goldman have found meaningful differences, and a method that is less sensitive to one corneal factor is not automatically a perfect reading of true pressure.
• 12:35
  SPEAKER_00: In the small cadaver eye monometry study mentioned earlier, Pascal readings averaged about 0.6 mm hergrams above the experimentally set intracameral pressure.
• 12:46
  SPEAKER_00: That is useful evidence about the device under those study conditions, not proof that it always measures a living person's pressure more accurately than Goldman.
• 12:56
  SPEAKER_00: Dynamic contour tonometry and intracameral pressure.
• 13:00
  SPEAKER_00: Ocular response analyzer.
• 13:02
  SPEAKER_00: Two pressure outputs.
• 13:03
  SPEAKER_00: How it works.
• 13:04
  SPEAKER_00: An ocular response analyzer uses an air pulse and sensors to observe the cornea as it moves inward and then outward.
• 13:11
  SPEAKER_00: No part of the instrument needs to touch the eye.
• 13:14
  SPEAKER_00: What it feels like.
• 13:15
  SPEAKER_00: The experience is similar to an airpuff test.
• 13:18
  SPEAKER_00: Numbing drops are not usually needed.
• 13:21
  SPEAKER_00: The device reports two different pressure estimates.
• 13:24
  SPEAKER_00: Goldman-correlated pressure is designed to approximate a goldman-like result.
• 13:29
  SPEAKER_00: Corneal compensated pressure uses the cornea's response during the test to try to reduce the effect of corneal properties.
• 13:36
  SPEAKER_00: It also reports corneal hysteresis, a measure related to how the cornea absorbs and releases energy during deformation.
• 13:44
  SPEAKER_00: The outputs are not interchangeable labels for the same number.
• 13:48
  SPEAKER_00: A review of studies found that the corneal compensated reading could differ from Goldman by several melomimidrangs in individual eyes, even where the average difference was modest.
• 13:58
  SPEAKER_00: Comparison of Goldman and Ocular Response Analyzer readings.
• 14:02
  SPEAKER_00: Corvus ST and biomechanically corrected pressure.
• 14:06
  SPEAKER_00: How it works.
• 14:07
  SPEAKER_00: Corvus ST combines an airpuff with a high-speed camera that records the cornea's movement.
• 14:12
  SPEAKER_00: Its software provides a standard pressure output and, with the relevant software, a biomechanically corrected pressure estimate.
• 14:20
  SPEAKER_00: What it feels like.
• 14:22
  SPEAKER_00: No contact or numbing drops are usually needed.
• 14:26
  SPEAKER_00: The test feels like an airpuff measurement.
• 14:28
  SPEAKER_00: Why it may help.
• 14:30
  SPEAKER_00: The additional imaging lets the device account for aspects of how the cornea deforms.
• 14:34
  SPEAKER_00: That may be helpful where standard measurements are complicated by corneal properties.
• 14:39
  SPEAKER_00: What remains uncertain?
• 14:41
  SPEAKER_00: Biomechanically corrected pressure is a calculated estimate, not an invasive measurement inside the eye.
• 14:47
  SPEAKER_00: In one study of people with open angle glaucoma or ocular hypertension, it averaged about 1.2 millimeter herbs higher than Goldman, with 95% limits of agreement from about minus 2.7 to plus 5.0 mmHgs.
• 15:02
  SPEAKER_00: Other studies have found different average relationships.
• 15:04
  SPEAKER_00: It can provide useful additional information, but it should not automatically be substituted for a long-standing Goldman series without a clinician's interpretation.
• 15:14
  SPEAKER_00: Corvus ST comparison in glaucoma and ocular hypertension, pneumatinometry.
• 15:20
  SPEAKER_00: How it works.
• 15:21
  SPEAKER_00: A pneumatinometer uses airflow and a soft-shaped contact tip to estimate pressure.
• 15:26
  SPEAKER_00: Some designs also report the eye's pulse-related pressure variation.
• 15:30
  SPEAKER_00: What it feels like, the tip touches the numbed eye, there is no air puff aimed from a distance.
• 15:36
  SPEAKER_00: The test can take longer than a quick screening puff.
• 15:39
  SPEAKER_00: Where it is used, it is available in some specialist and hospital settings.
• 15:45
  SPEAKER_00: The American Academy of Ophthalmology lists pneumatinometry among alternatives that may be considered when the cornea is diseased or altered.
• 15:54
  SPEAKER_00: That does not mean it is automatically the most accurate option for every abnormal cornea.
• 15:59
  SPEAKER_00: The choice depends on the specific surface problem and the equipment and expertise available.
• 16:04
  SPEAKER_00: American Academy of Ophthalmology Guidance on Pressure Assessment in Diseased Corneas.
• 16:10
  SPEAKER_00: Transpalpabral devices, testing through the eyelid.
• 16:14
  SPEAKER_00: How they work.
• 16:15
  SPEAKER_00: A handheld device is placed over the closed eyelid, commonly near the upper lid, and estimates pressure from the response of the eyelid and tissues beneath it.
• 16:24
  SPEAKER_00: What it feels like.
• 16:25
  SPEAKER_00: The device presses lightly against the eyelid.
• 16:28
  SPEAKER_00: There is no direct corneal contact and no air puff where they are used.
• 16:33
  SPEAKER_00: These devices are uncommon alternatives, sometimes considered when corneal contact is not practical.
• 16:39
  SPEAKER_00: Their readings have shown wide disagreement with Goldman.
• 16:42
  SPEAKER_00: A systematic review reported pooled limits of agreement of roughly minus 7 to plus 6 mm HER grams, with fewer than half of readings within 2 mmHHH grams of Goldman.
• 16:53
  SPEAKER_00: The method should not be assumed to avoid measurement problems simply because it does not touch the cornea.
• 16:59
  SPEAKER_00: European Glaucoma Society Summary of Tonometer Agreement.
• 17:03
  SPEAKER_00: Sheets indentation telometry.
• 17:05
  SPEAKER_00: How it works.
• 17:06
  SPEAKER_00: A weighted plunger rests on the numbed cornea while the patient lies down.
• 17:10
  SPEAKER_00: The device estimates pressure from how far the cornea indents.
• 17:14
  SPEAKER_00: What it feels like.
• 17:15
  SPEAKER_00: Numbing drops are used, and the instrument briefly rests on the eye.
• 17:19
  SPEAKER_00: You need to lie flat and keep still.
• 17:22
  SPEAKER_00: Where it is used, this is mainly a historical or uncommon approach in modern eye clinics.
• 17:28
  SPEAKER_00: Because readings depend not only on pressure but also on the rigidity of the eye wall, positioning, and instrument condition, it is not generally considered a close substitute for contemporary applination measurements.
• 17:40
  SPEAKER_00: Overview of tonometry methods.
• 17:42
  SPEAKER_00: Contact lens sensors and implants, pressure readings versus pressure-related signals.
• 17:48
  SPEAKER_00: Not every device that tracks eye pressure gives a pressure number in miminaher grags.
• 17:53
  SPEAKER_00: Sensimed triggerfish, a trend signal, not mimher drams.
• 17:57
  SPEAKER_00: The triggerfish is a special contact lens worn for a limited monitoring period.
• 18:02
  SPEAKER_00: Its sensor detects small changes in the shape or dimensions of the eye that are related to pressure changes.
• 18:08
  SPEAKER_00: It reports a pressure-related pattern, not a conventional IOP reading in miminahergrams.
• 18:13
  SPEAKER_00: The United States Food and Drug Administration describes its role as helping identify the time window when a conventional pressure check may be useful.
• 18:22
  SPEAKER_00: It is not itself a diagnostic pressure measurement.
• 18:26
  SPEAKER_00: Food and Drug Administration description of trigger fish, implantable pressure sensors, mimitaher dranks, but not routine care.
• 18:34
  SPEAKER_00: Some implantable systems are designed to report pressure in mimimitahergi through an external reader.
• 18:40
  SPEAKER_00: They require surgery and have been studied in small selected groups, including people having other eye surgery or glaucoma procedures.
• 18:48
  SPEAKER_00: In one 12-month study of 22 people with glaucoma, an IMATE I.O.
• 18:52
  SPEAKER_00: implant gave readings that averaged 3.2 millimeter hergrams higher than Goldman.
• 18:57
  SPEAKER_00: That difference illustrates why an implanted device still needs to be interpreted against the patient's clinical history and the device's own baseline.
• 19:05
  SPEAKER_00: Other implantable sensors remain investigational or limited to specialized clinical programs.
• 19:11
  SPEAKER_00: They are not routine home monitors for most patients.
• 19:15
  SPEAKER_00: IMate I.O.
• 19:16
  SPEAKER_00: 12-month study.
• 19:18
  SPEAKER_00: Practical distinction.
• 19:19
  SPEAKER_00: A contact lens system such as Triggerfish supplies a pressure-related pattern or trend.
• 19:24
  SPEAKER_00: An implantable pressure sensor may report a calibrated Memina HERG value.
• 19:29
  SPEAKER_00: A trend signal is not interchangeable with an absolute pressure reading.
• 19:33
  SPEAKER_00: Why might three tests give three different results on the same day?
• 19:37
  SPEAKER_00: Imagine an airpuff test reads 22mm grubs, a clinic rebound test reads 24, and Goldman reads 21.
• 19:45
  SPEAKER_00: That does not by itself prove that your pressure rose and fell.
• 19:48
  SPEAKER_00: Possible reasons include different measurement principles.
• 19:52
  SPEAKER_00: One device observes an air-driven response, another records a probe's rebound, Goldman observes the force needed to flatten the cornea.
• 20:00
  SPEAKER_00: Different effects of the cornea, thickness matters, but so do curvature, stiffness, hydration, scarring, and surface regularity.
• 20:09
  SPEAKER_00: Normal pressure changes.
• 20:10
  SPEAKER_00: Pressure can vary over the day and with posture.
• 20:13
  SPEAKER_00: Test technique.
• 20:14
  SPEAKER_00: Squeezing, looking in the wrong direction, or being uncomfortable can affect the result.
• 20:19
  SPEAKER_00: Device condition or calibration.
• 20:22
  SPEAKER_00: Equipment can be out of calibration, or a device model may have a consistent offset.
• 20:27
  SPEAKER_00: This is why clinicians often use a screening reading as a reason to check further, rather than treating numbers from different devices as directly interchangeable.
• 20:36
  SPEAKER_00: Is a 2-3mm hergrad difference meaningful?
• 20:39
  SPEAKER_00: Sometimes, but not automatically.
• 20:42
  SPEAKER_00: A difference of 2-3 mm hergrams between two types of tonometer may fall within the observed spread between methods.
• 20:49
  SPEAKER_00: It may matter more if it happens repeatedly on the same method, occurs near an individual treatment target, or is seen alongside changes in the optic nerve or visual field.
• 21:00
  SPEAKER_00: A larger or unexpected discrepancy can be a reason to repeat the measurement carefully and consider another method, especially if the reading conflicts with past results or the examination.
• 21:12
  SPEAKER_00: The United Kingdom's National Institute for Health and Care Excellence recommends repeating a high measurement in relevant assessment situations rather than relying on a single reading.
• 21:22
  SPEAKER_00: This is clinical context, not a universal rule that one particular difference always means danger.
• 21:29
  SPEAKER_00: What can affect the reading?
• 21:31
  SPEAKER_00: Corneal thickness and biomechanics.
• 21:34
  SPEAKER_00: Goldman and several other common methods can read higher, on average, in thicker corneas and lower, on average, in thinner corneas.
• 21:42
  SPEAKER_00: But thickness is only one influence, and it cannot tell a clinician exactly how much to add or subtract for one person.
• 21:49
  SPEAKER_00: Two corneas of the same thickness can have different stiffness or flexibility.
• 21:54
  SPEAKER_00: Corneal hysteresis and other biomechanical features can also matter.
• 21:58
  SPEAKER_00: European Glaucoma Society.
• 22:00
  SPEAKER_00: Guidance treats corneal thickness as information that helps interpret risk and readings, not as a reason to apply a universal arithmetic correction.
• 22:09
  SPEAKER_00: European Glaucoma Society Guidance on Corneal Thickness.
• 22:13
  SPEAKER_00: Why not use a fixed correction table?
• 22:15
  SPEAKER_00: A table based only on thickness cannot account for each person's corneal stiffness, shape, surface, or surgical history.
• 22:23
  SPEAKER_00: It may create a number that looks more precise without being more accurate.
• 22:27
  SPEAKER_00: Previous LASIK or PRK LASIC and photorefractive keratectomy, PRK, alter the cornea.
• 22:33
  SPEAKER_00: Goldman readings after these procedures can be lower than before surgery, in part because the cornea is thinner and its structure has changed.
• 22:42
  SPEAKER_00: A systematic review found an average reduction in Goldman readings after LASIK of about 3.2 mm her gram, with substantial variation between studies and people.
• 22:52
  SPEAKER_00: This is a group average, not an amount to add back to an individual's reading.
• 22:57
  SPEAKER_00: Systematic review of pressure measurements after LASIK and PRK.
• 23:00
  SPEAKER_00: Tell your eye care professional if you have had refractive surgery.
• 23:04
  SPEAKER_00: They may use a second method, such as dynamic contour tonometry, an ocular response analyzer, or the biomechanically corrected corvus ST output, to add perspective.
• 23:15
  SPEAKER_00: No alternative should be treated as infallible.
• 23:18
  SPEAKER_00: Astigmatism, dry eye, and corneal disease.
• 23:21
  SPEAKER_00: Astigmatism can affect Goldman readings if the prism is not aligned appropriately.
• 23:26
  SPEAKER_00: One study estimated an error of about 1 mmHg for every four diopters of regular corneal astigmatism in the tested orientation.
• 23:34
  SPEAKER_00: A clinician can adjust the prism position or compare readings in different directions.
• 23:40
  SPEAKER_00: Study of astigmatism and goldman readings.
• 23:43
  SPEAKER_00: Dry eye or an unstable tear film may make the contact point or its visual endpoint harder to judge.
• 23:49
  SPEAKER_00: The amount of effect varies, an imperfect surface does not mean every reading is unusable.
• 23:54
  SPEAKER_00: Corneal swelling, scarring, disease, or previous corneal surgery can affect several techniques, particularly those relying on corneal flattening.
• 24:03
  SPEAKER_00: The American Academy of Ophthalmology advises considering alternatives when the cornea is diseased or surgically altered.
• 24:10
  SPEAKER_00: No single alternative is best for every condition.
• 24:13
  SPEAKER_00: American Academy of Ophthalmology Guidance on Diseased Corneas.
• 24:17
  SPEAKER_00: Squeezing, breath holding, posture, time of day, and calibration.
• 24:22
  SPEAKER_00: Squeezing the eyelids or holding them shut tightly can raise a reading.
• 24:27
  SPEAKER_00: If your lids need to be held open, the clinician should avoid pressing on the eye.
• 24:32
  SPEAKER_00: Straining or holding your breath, especially bearing down against a closed throat, can affect pressure.
• 24:38
  SPEAKER_00: Try to breathe normally and relax.
• 24:40
  SPEAKER_00: Posture matters.
• 24:42
  SPEAKER_00: Pressure often rises when moving from sitting to lying down, although the amount varies.
• 24:46
  SPEAKER_00: A clinic measurement taken sitting upright is not necessarily directly comparable with a reading taken lying flat.
• 24:53
  SPEAKER_00: Time of day matters.
• 24:54
  SPEAKER_00: One appointment samples one moment.
• 24:57
  SPEAKER_00: Some people have changes at other times, including outside usual clinic hours.
• 25:02
  SPEAKER_00: Calibration and technique matter.
• 25:04
  SPEAKER_00: Goldman is a well-established reference, but it can still be miscalibrated or performed inconsistently.
• 25:10
  SPEAKER_00: In one hospital calibration study, many Goldman instruments fell outside the manufacturer's tightest recommended tolerance, and some had errors greater than 2mm herdrans.
• 25:20
  SPEAKER_00: This is a reminder that no method is immune to equipment checks and operator skill.
• 25:26
  SPEAKER_00: Goldman calibration study, very low or very high readings, and after glaucoma surgery, methods do not necessarily perform equally well at the extremes.
• 25:35
  SPEAKER_00: For example, in a study of eyes after vitreoretinal surgery, eye care rebound readings averaged about 2 mm hergram lower than Goldman when pressure was below 10 mm Herbs and about 3.8 mm hergrams higher when pressure was at least 23 millimeter herbs.
• 25:52
  SPEAKER_00: These results came from a particular postoperative group and should not be treated as a fixed rule for all patients.
• 25:58
  SPEAKER_00: Postoperative comparison of rebound, tonopen, and goldman.
• 26:02
  SPEAKER_00: After glaucoma surgery, a very low reading, a high reading, or a result that does not fit the eye's appearance may justify repeat testing or a second approach.
• 26:12
  SPEAKER_00: The surface may be altered, the target pressure may be individualized, and the care team may need to consider the type of operation and other examination findings.
• 26:22
  SPEAKER_00: Do not change treatment based on one surprising number.
• 26:25
  SPEAKER_00: Which method might be useful in different situations.
• 26:29
  SPEAKER_00: Routine screening.
• 26:30
  SPEAKER_00: An airpuff or rebound test can provide a quick estimate.
• 26:33
  SPEAKER_00: A raised or concerning result may call for confirmation.
• 26:37
  SPEAKER_00: Ongoing glaucoma monitoring.
• 26:39
  SPEAKER_00: Goldman is commonly used because it is established and allows comparison with previous readings.
• 26:45
  SPEAKER_00: Using the same method consistently can help make trends easier to interpret.
• 26:50
  SPEAKER_00: Children are people unable to sit at a slit lamp.
• 26:53
  SPEAKER_00: Rebound telometry may be easier because numbing drops are not usually needed.
• 26:58
  SPEAKER_00: Perkins may help when a patient needs to lie down and can tolerate a contact test.
• 27:03
  SPEAKER_00: Bedside or emergency assessment.
• 27:05
  SPEAKER_00: A handheld device such as tonopen or Perkins may be practical.
• 27:09
  SPEAKER_00: The choice depends on the patient, the eye surface, and the clinician's skill.
• 27:13
  SPEAKER_00: An altered or diseased cornea.
• 27:15
  SPEAKER_00: A clinician may consider more than one method, such as tonopen, pneumatonometry, dynamic contour tonometry, the ocular response analyzer, or Corvus ST.
• 27:25
  SPEAKER_00: The best option depends on the specific corneal change.
• 27:29
  SPEAKER_00: Home monitoring.
• 27:30
  SPEAKER_00: Eye care home may be useful for selected patients who can learn the technique and review results with their eye care professional.
• 27:37
  SPEAKER_00: These are practical patterns, not a universal device ranking.
• 27:41
  SPEAKER_00: The latest European Glaucoma Society Guidelines and National Guidance emphasize interpretation in context, while recognizing that evidence is not equally strong for every method.
• 27:53
  SPEAKER_00: European Glaucoma Society Guidelines, 6th edition.
• 27:56
  SPEAKER_00: Why an eye pressure reading cannot diagnose glaucoma by itself?
• 28:00
  SPEAKER_00: Glaucoma is assessed by looking for characteristic damage to the optic nerve and changes in visual function alongside pressure and other risk factors.
• 28:09
  SPEAKER_00: Some people have elevated pressure without glaucoma, and some people develop glaucoma despite readings that are not elevated.
• 28:16
  SPEAKER_00: Pressure is important, but one pressure result cannot by itself establish whether someone has glaucoma or whether their disease is controlled.
• 28:26
  SPEAKER_00: A comprehensive assessment may include examination or imaging of the optic nerve, visual field testing, corneal thickness, the drainage angle, and change over time.
• 28:37
  SPEAKER_00: The National Eye Institute states that tonometry alone is not sufficient to diagnose glaucoma, and the National Institute for Health and Care Excellence advises against basing referral decisions solely on a non-contact pressure reading.
• 28:51
  SPEAKER_00: National Eye Institute on Glaucoma Detection, National Institute for Health and Care Excellence glaucoma recommendations.
• 28:58
  SPEAKER_00: Questions to ask at your next appointment.
• 29:01
  SPEAKER_00: Which device measured my pressure today?
• 29:03
  SPEAKER_00: Was the reading repeated and were the results similar?
• 29:06
  SPEAKER_00: Could my cornea, dry eye, astigmatism, or past lassoc or PRK affect this result?
• 29:13
  SPEAKER_00: Should I have a reading with a different method or at another time of day?
• 29:17
  SPEAKER_00: If I use a home monitor, how should its readings be compared with my clinic readings?
• 29:21
  SPEAKER_00: How does this number fit with my optic nerve, visual field, and treatment target?
• 29:26
  SPEAKER_00: Bottom line, the puff of air, the blue-lit prism, the handheld probe, and specialist corneal response devices all estimate pressure in different ways.
• 29:36
  SPEAKER_00: A 2-3mm drive difference between methods is not automatically a meaningful change.
• 29:42
  SPEAKER_00: A larger or unexpected difference may be a reason to repeat or check the measurement, particularly if it conflicts with your history or examination.
• 29:50
  SPEAKER_00: The most helpful result is not necessarily the highest tech device's number.
• 29:55
  SPEAKER_00: It is a carefully obtained, appropriately interpreted reading that can be compared over time with another method considered when the cornea, the pressure range, the patient, or the clinical situation calls for it.
• 30:08
  SPEAKER_00: Work with your eye care professional to interpret readings and choose a suitable approach, and do not change glaucoma treatment based on a device score or one isolated measurement.
• 30:19
  SPEAKER_00: All links to sources are available in the text version of this article.
• 30:23
  SPEAKER_00: You can find the full article at VisualFieldTest.com.
• 30:27
  SPEAKER_00: Thanks for listening.
• 30:28
  SPEAKER_00: To check your visual field, click the link at the bottom of this article or visit visualfieldtest.com.