Pachymetry is a type of ophthalmological examination that measures the thickness of the cornea in its center. It is a very important diagnostic test that should be performed in every patient diagnosed for glaucoma.

Why ispachymetrythat iscorneal thickness testimportant in glaucoma diagnosis? Studies have shown that the thickness of the cornea has a significant impact on the results of the measurement of intraocular pressure. The average central corneal thickness of a he althy person is 540 +/- 30 micrometers and most devices measuring intraocular pressure are calibrated to this thickness. If the patient's cornea is significantly thinner or thicker, an appropriate correction should be included in the pressure value obtained by the test.

Thinner corneal thickness is often found in black people, patients with myopia, dry eye syndrome, corneal degeneration, or Down syndrome. It is also lower in people with myopia who have undergone laser correction of this defect.

In turn, greater corneal thickness usually occurs in people of the yellow race, but can also occur in patients with hyperopia, diabetes, and in the case of corneal degeneration or scarring. Thicker cornea may also occur if pachymetry is measured in the morning (this is due to a temporary slight swelling of the cornea and hence an increase in thickness) and in contact lens wearers. Therefore, these factors should be taken into account when examining the thickness of the cornea.

When pachymetry is needed

Assessment of central corneal thickness is very important in assessing pressure in patients with ocular hypertension and primary normal pressure glaucoma. In patients with a thick cornea, the pressure measurement may be overstated, and if the central thickness of the cornea is not taken into account, the patient may receive unnecessary pressure-lowering treatment. If the cornea is thin, the pressure may be underestimated and the glaucoma patient may receive insufficient treatment. The relevant amendment is read from the table.

Corneal thickness measurement is extremely important in diagnosed cases:

  • ocular hypertension - measuring the thickness of the cornea allows you to verify the diagnosis and determine the appropriate treatment as wellforecasts
  • glaucoma with normal pressure - verification of the diagnosis and determination of the target pressure value
  • high-pressure glaucoma - especially in cases of poor response to treatment, due to the possibility of lower corneal permeability for drugs
  • in the early diagnosis of glaucoma - measuring the thickness of the cornea helps in determining the risk of glaucoma and its progression. A thin cornea is a prognostic and prognostic negative factor, it is correlated with a higher risk of glaucoma in a patient

Glaucoma - what should you know about it?

Methods of measuring the thickness of the cornea

There are currently two methods of measuring corneal thickness, the first of which istactile pachymetry , performed using ultrasonic tactile pachymetry. The test requires contact of the tip of the apparatus with the patient's cornea. The examination is not painful because the surface of the cornea is previously anesthetized with drops. Then a tip is brought closer to the eye, which looks a bit like the tip of a ballpoint pen. The instrument takes several measurements of the central corneal thickness which are then averaged. The obtained measurement result allows reading from the table and then making the appropriate correction for the value of intraocular pressure. The advantage of this method is its simplicity, availability and relatively low price. The undoubted disadvantages are the contact of the device tip with the cornea, the need for drip anesthesia of the cornea and the measurement error resulting from the pressure of the device tip on the patient's cornea.

The second method used istouchless pachymetry . The examination is performed using laser corneal tomography. The test allows you to measure the thickness of the cornea at its center and to map the thickness of the entire cornea, it also allows you to assess the cornea for abnormalities in its structure, as well as to assess the structures of the anterior segment of the eye, such as the depth of the anterior chamber and the width of the traverse angle. The undoubted advantages of this method include contactlessness limiting the possibility of infection and unpleasant sensations, high precision of the method, no influence of the examiner on the accuracy of the examination and the possibility of simultaneous tomographic evaluation of the entire anterior segment of the eye. The disadvantage of the method is the availability of it only in highly specialized glaucoma clinics.

Please note that both methods are not interchangeable when using both methods. The results obtained with both types of apparatus are correlated, but there are differences between them. The correction of the height of the intraocular pressure must be made according to the correctionscalculated for a given measurement method.

About the authorBarbara Polaczek-Krupa, MD, PhD, specialist in eye diseases, Centrum Opulystowa Targowa 2, Warsaw

Dr. Barbara Polaczek-Krupa, MD, initiator and founder of the T2 Center. She specializes in modern diagnostics and treatment of glaucoma - this was also the subject of her doctoral thesis defended with honors in 2010, Dr. med. Polaczek-Krupa has been gaining experience for 22 years, since she started working at the Ophthalmology Clinic of the CMKP in Warsaw, with which she was tied in the years 1994-2014. During this period, she obtained two degrees of specialization in ophthalmology and the title of doctor of medical sciences. In the years 2002-2016 she worked at the Institute of Glaucoma and Eye Diseases in Warsaw, where she gained medical knowledge and experience by consulting patients from all over Poland and abroad. The Postgraduate Medical Education Center is a lecturer at courses and training for doctors specializing in ophthalmology and primary he alth care. He is the author or co-author of numerous publications in scientific journals. Member of the Polish Ophthalmology Society (PTO) and the European Glaucoma Society (EGS).

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