Comparison of Diaton transpalpebral tonometer with applanation tonometry in keratoconus

Easyton® transpalpebral versus Perkins applanation tonometry in different populations

OBJECTIVE

 To compare intraocular pressure (IOP) measurements obtained using the new transpalpebral Easyton® tonometer and Perkins applanation tonometer (PAT) in three different clinical populations.

METHODS

The participants of this prospective study were 84 subjects divided into the groups: 22 healthy children (G1), 42 healthy adults (G2), and 20 adult patients with primary open angle glaucoma (G3). The data recorded in 84 eyes of these subjects were age, sex, gender, central corneal thickness (CCT), and axial length (AL). In all eyes, IOP was determined in the same examination room by the same experienced examiner using Easyton® and PAT in random order.

RESULTS

 Mean differences in IOP readings between Easyton® and PAT were 0.45 ± 1.97 (p = 0.295), - 0.15 ± 2.13 (p = 0.654), - 1.65 ± 3.22 (p = 0.033), and - 0.018 ± 2.50 mmHg (p = 0.500) in the groups G1, G2, G3, and whole sample (G4), respectively. Correlations between Easyton® and PAT IOP values were 0.668 (p = 0.001) for G1, 0.463 (p = 0.002) for G2, 0.680 (p < 0.001) for G3, and 0.605 (p < 0.001) for G4. Moderate to good agreement between the two tonometers was found in all groups according to intraclass correlation coefficients, which were 0.794 (p < 0.001) for G1, 0.632 (p < 0.001) for G2, 0.809 (p < 0.001) for G3, and 0.740 (p < 0.001) for G4. The lower and upper limits of agreement between the devices were - 5.1 and 4.7 mmHg, respectively, in the complete group. No correlation was noted between CCT or AL and the Easyton® IOP measurements.

CONCLUSION

IOP measurements obtained with Easyton® and PAT show an acceptable level of agreement mainly in healthy individuals, recommending it for IOP screening in children and in patients in which PAT measurement may be impared as patients with hemifacial spasms, corneal irregularities, or reduced mobility. It is not recommended for glaucoma patients follow-up.

Agreement among Goldmann Applanation Tonometer, Easyton Transpalpebral Tonometer, Tonopen, and Icare in Patients with Keratoconus

Objectives

The objective of the study is to evaluate the agreement between Goldmann applanation tonometer (GAT) and Easyton transpalpebral tonometer, Tonopen, and Icare in patients with Keratoconus.

Methods

This cross-sectional study included 46 eyes of 26 patients with keratoconus. Intraocular pressure (IOP) is measured using easyton, icare, tonopen, and GAT. Measurements were compared and the influences of corneal topographic variables on IOP measurement were evaluated. Bland-Altman plots were used for assessing agreement between different tonometers.

Results

The mean age of the participants was 24.08±6.76 (range, 18-47) years (15 males and 11 females). The highest of the mean IOP values measured with different tonometers was obtained with Easyton (12.33±1.65), followed by Tonopen (11.59±2.17), GAT (10.67±1.52), and Icare (10.04±2.33). The mean IOP value measured with Easyton was significantly higher than that measured with GAT (p<0.001). There was no significant difference between GAT and either Tonopen (p=0.154) or Icare measurements (p=0.732). There was no significant difference between Tonopen and Easyton measurements (p=0.421). Icare measurements were correlated with central corneal thickness and keratometric values. GAT measurements were correlated with only Kmax. Thirty-eight (82.6%) of the differences were within the agreement limits (assumed clinically important deviation of up to ±2 mmHg) of GAT and Tonopen, 73.9% (n=34) were within the agreement limits of GAT and Icare, and 78.3% (n=36) were within the agreement limits of GAT and Easyton.

Conclusion

Compared with GAT, the gold standard method, Easyton IOP readings were higher, while both Tonopen and Icare readings were similar to GAT. All three tonometers showed acceptable agreement with the GAT, however, Tonopen showed the greatest agreement.

[Tonometry: Review and Perspectives]

Reliable and repeated IOP measurement are essential in the diagnosis and treatment of glaucoma. In this first part of this review, besides the physiological basics, contact tonometry will be presented, which is both the first instrumental method with the indentation tonometers and the gold standard with the Goldmann applanation tonometer. Both methods and subsequently developments will be discussed.

Tonometrie: Rückblick und Ausblick (Teil 1)

Der intraokulare Druck (IOD) ist ein wichtiger physikalischer Parameter der Physiologie des Auges. Ein erhöhter IOD wurde früh als Ätiologie für Augenerkrankungen vermutet. In diesem 1. Teil des Beitrags wird neben den physiologischen Grundlagen die Kontakttonometrie vorgestellt, die sowohl die erste instrumentelle Methode mit den Indentationstonometern als auch den Goldstandard mit dem Goldmann-Applanationstonometer darstellt.

Trans Palpebral Intraocular Pressure Measurement by Diaton Tonometer and Central Corneal Thickness in Eyes before and after Transepithelial Photorefractive Keratectomy of Saudi Patients

PURPOSE

The influence of central corneal thickness (CCT) on intraocular pressure (IOP) measurement by Diaton is debatable. We present a correlation of CCT to transpalpebral IOP (tpIOP) and its determinants in patients undergoing transepithelial photorefractive keratectomy (TPRK) in Saudi Arabia.

METHODS

In this cross-sectional study held in 2022, the IOP of patients undergoing TPRK was measured by Diaton tonometer. The CCT was measured before and 1 week after refractive surgery. The correlation coefficient of CCT and IOP and its Pearson P value were estimated. The effects of gender, type of refractive error (RE), and corneal epithelial thickness (CET) on the correlation of IOP to CCT were reviewed.

RESULTS

We studied 202 eyes in 101 patients (Male: Female, 47:53; age 25.7 ± 5.8 years). The tpIOP was 15.1 ± 2.8 mmHg before, 15.9 ± 2.8 mmHg 1 week after, and 15.7 ± 4.1 mmHg 1 month after TPRK. The CCT was significantly correlated with tpIOP before surgery (Pearson correlation 0.168, P = 0.017) and after tPRK (Pearson correlation 0.246, P < 0.001). Gender (P = 0.96), CET (P = 0.43), and type of RE (P = 0.99) were not significant determinants of correlation between CCT and tpIOP before TPRK. The correlation of tpIOP and CCT was not affected by gender (P = 0.07), CET (P = 0.39), and type of RE (P = 0.13).

CONCLUSION

CCT should be considered before interpreting tpIOP measured by with Diaton. Diaton could be a useful tool to monitor IOP changes in young patients undergoing refractive surgery.

[Examination of patients with glaucoma during the COVID-19 pandemic]

PURPOSE

To evaluate the efficacy of the optimal examination technique for patients with glaucoma during the COVID-19 pandemic that includes one of the safest methods of tonometry [transpalpebral tonometry (TPT), contour dynamic tonometry (CDT) and Icare rebound tonometry (RBT)] in combination with spectral domain optical coherence tomography (SD-OCT) and optical coherence tomography angiography (OCTA).

MATERIAL AND METHODS

The study included 65 patients with primary open-angle glaucoma (POAG) who sought medical aid at the Ophthalmological Center of FMBA during the COVID-19 pandemic; they were examined using three tonometry methods: RBT, TPT and CDT. All patients underwent central corneal thickness measurement, perimetry, OCT and OCTA with assessment of vessel density (VD) of the superficial plexus in the macula (whole image macula) and peripapillary retina (PPR).

RESULTS

High correlation was found between the results obtained with RBT, TPT and CDT. None of the methods showed a correlation between IOP and corneal thickness. The correlations between IOP and OCTA parameters were obtained: IOP_TPT and VD_PPR in the inferior temporal sector (r= -0.386, p=0.027), IOP_RBT and VD whole image macula (r= -0.69, p=0.019), and in the macula inferior hemisphere (r= -0.75, p=0.008), as well as between the ocular pulse amplitude (OPA) and VD in the macular inferior hemisphere (r=0.380, p=0.039). The OCTA parameters had a moderate, but significant correlation with the perimetric indices.

CONCLUSIONS

Tonometry methods (TPB, CDT and RBT) exhibit high correlation with each other and no correlation with corneal thickness. IOP parameters measured by different methods, especially using the Icare tonometer, correlate with OCTA parameters, and the latter - with perimetric indices. The combination of these tonometry methods with SD-OCT and OCTA is optimal for examining patients during the pandemic.

Effects of Scleral Contact Lenses for Keratoconus Management on Visual Quality and Intraocular Pressure

Purpose

To evaluate the visual acuity level achieved by scleral contact lens (CL) fitting in patients affected by keratoconus and to evaluate possible intraocular pressure (IOP) changes during the scleral CL wear using a transpalpebral tonometer.

Methods

In a prospective case series a comparison was made between visual acuity obtained with glasses, RGP and 16.8mm diameter scleral CL in 30 consecutive patients affected by keratoconus. IOP was tested during scleral CL wear by transpalpebral Diaton Tonometer (DT) and also by Goldmann Applanation Tonometer (GAT) before and after scleral CL wear.

Results

The mean logMAR visual acuity improved from 0.2±0.25SD with glasses and 0.1±0.02SD with RGP, to −0.002±0.041SD when using the scleral CL (p<0.05). The mean IOP value before scleral CL wear was 12.93mmHg±2.20SD when measured with GAT and 7.85mmHg±2.27SD when measured with DT. During scleral CL wear, IOP was assessed through DT, with a mean value of 8.86mmHg±2.36SD; values were stable after 8 hours of scleral CL use. Immediately after scleral CL removal, the mean IOP measured with GAT was 12.85mmHg ±2.40SD and the mean IOP measured with DT was 7.66mmHg±1.88SD. Therefore, during scleral CL wear, it was evidenced a small but statistically significant increase of the mean IOP value (1.01mmHg; p<0.01), with a reversion to values prior to application when scleral CL was removed.

Conclusion

Scleral CLs remarkably improved visual acuity in keratoconus patients when compared to glasses or RGP contact lenses. Even if it was evidenced a small increase of the mean IOP value during their wear, it may not be significant in otherwise healthy eyes. Statistical analysis demonstrated good agreement between GAT and DT but their numerical values presented a constant gap, that should be taken into account when there is a need to relate the DT values to the reference ones.

Novel dynamic corneal response parameters in a practice use: a critical review

Background

Non-contact tonometers based on the method using air puff and Scheimpflug’s fast camera are one of the latest devices allowing the measurement of intraocular pressure and additional biomechanical parameters of the cornea. Biomechanical features significantly affect changes in intraocular pressure values, as well as their changes, may indicate the possibility of corneal ectasia. This work presents the latest and already known biomechanical parameters available in the new offered software. The authors focused on their practical application and the diagnostic credibility indicated in the literature.

Discussion

An overview of available literature indicates the importance of new dynamic corneal parameters. The latest parameters developed on the basis of biomechanics analysis of corneal deformation process, available in non-contact tonometers using Scheimpflug’s fast camera, are used in the evaluation of laser refractive surgery procedures, e.g. LASIK procedure. In addition, the assessment of changes in biomechanically corrected intraocular pressure confirms its independence from changes in the corneal biomechanics which may allow an intraocular pressure real assessment. The newly developed Corvis Biomechanical Index combined with the corneal tomography and topography assessment is an important aid in the classification of patients with keratoconus.

Conclusion

New parameters characterising corneal deformation, including Corvis Biomechanical Index and biomechanical compensated intraocular pressure, significantly extend the diagnostic capabilities of this device and may be helpful in assessing corneal diseases of the eye. Nevertheless, further research is needed to confirm their diagnostic pertinence.