Comparison of Maklakov tonometry (10 grams) and corneal compensated intraocular pressure

Background Traditional Maklakoff tonometry does not take into account individual biomechanical properties of the eye, relying on average rigidity values ​​measured in vitro. In contrast, corneal compensated IOPcc, measured by bidirectional applanation, takes these individual characteristics into account and has been shown in the literature to be of greater diagnostic value in glaucoma [1–3]. Comparison of Maklakoff and IOPcc tonometry values ​​in the same patient population may change our understanding of the value of tonometers. Objective To determine IOPcc ranges corresponding to specific Maklakoff tonometry values ​​(with a 10-gram weight) in a sufficient number of patients, and to study the relationship between the Maklakoff indentation diameter and intraocular pressure, taking into account individual differences in corneal biomechanical properties [4, 5]. Material and methods A prospective comparative analysis included data from 14,440 eyes of 7,220 patients (mean age 60.1 ± 10.8 years) with primary open-angle glaucoma (POAG) or suspected glaucoma. The intraocular pressure values ​​obtained by Maklakov tonometry using a 10 g weight were compared with corneal-compensated intraocular pressure (IOPcc). Inclusion criteria were: the presence of a high-quality corneogram and IOPcc values ​​in the range from 6 to 35 mmHg. The diameter of the applanation print was measured with a caliper with an accuracy of 0.1 mm in accordance with the recommendations of the tonometer manufacturer. Results Variability in ocular structure affects IOP readings with the same print size after tonometry. A nomogram of IOPcc and print size correspondence was created for the Maklakov tonometer (10 g). The equation IOP=4.14×D2 -62.4×D+248 can serve as a calibration formula for accurate measurements in the middle and lower ranges of ophthalmotonus. Conclusion The Maklakov tonometer readings (10 g) allow determining the probable range of the patient's true intraocular pressure. This approach increases the value of conventional tonometry when it is impossible to more accurately assess the biomechanics of the eye. Key words: glaucoma; Maklakov tonometry; corneal-compensated pressure