[Impression and applanation tonometry in irregular corneas. Comparison with intraocular needle tonometry]

Area of Science:

• Ophthalmology
• Glaucoma diagnostics
• Corneal disease management

Background:

• Applanation tonometry (Goldmann, Perkins) often yields falsely low intraocular pressure (IOP) readings in eyes with corneal pathology.
• Previous studies indicated a discrepancy between applanation tonometry and intraocular needle tonometry in such cases.

Purpose of the Study:

• To compare the precision of Schioetz impression tonometry against applanation tonometry for IOP measurement in eyes with corneal disorders.
• To determine if impression tonometry offers a more reliable IOP assessment than applanation tonometry in compromised corneas.

Main Methods:

• A study involving 75 eyes with suspected glaucoma and corneal disorders.
• Performed applanation tonometry, impression tonometry (at various weights), and intraocular needle tonometry.
• Repeated applanation tonometry post-impression to assess potential tonography effects.

Main Results:

• Both applanation and impression tonometry (at 5.5g, 7.5g, 10.0g) showed statistically significant underestimation of IOP compared to intraocular needle tonometry (P < 0.001).
• The mean differences were -4.1 mmHg for applanation and -4.3 to -4.8 mmHg for impression tonometry.
• No statistically significant difference was found between applanation and impression tonometry results themselves.

Conclusions:

• Neither applanation nor impression tonometry provides reliable IOP measurements in eyes with corneal pathology.
• Intraocular needle tonometry is the only consistently reliable method for IOP assessment in patients with corneal disorders.