This time of year, many ODs consider purchasing new equipment. Intraocular pressure (IOP)-measuring technology is not often on this list, as many of us rely on Goldmann applanation tonometry (GAT). Yet, as our understanding of corneal biomechanics has evolved, many newer devices aim to provide accurate IOP readings as well.
Here are the major options:
Applanation
The Correcting Applanation Tonometry Surface (CATS) prism modifies the traditional Goldmann prism by adjusting for corneal curvature and biomechanics. It reduces measurement errors related to central corneal thickness (CCT) and rigidity. This prism is less reliant on corneal parameters.1
Non-Contact
These devices, used for glaucoma screenings, employ sensors that detect the force of air needed to flatten the cornea. They can be available with autokeratometers, autorefractors, and noncontact pachymeters.
One type of device measures IOP via an air pulse and optical detection system that records both inward and outward applanation. Further, it provides a corneal-compensated IOP, which minimizes the impact of corneal properties. In postrefractive surgery eyes, where corneal architecture is altered, corneal-compensated IOP has shown better agreement with expected IOP.2
This device also provides a reading of corneal hysteresis, a predictor of both glaucoma conversion and progression.3
Indentation
A handheld applanation tono-meter that requires minimal topical anesthesia uses a micro strain gauge transducer and microprocessor to provide an averaged IOP reading from multiple gentle contacts with the cornea.
It is influenced by corneal thickness and operator technique, and tends to show slightly high readings, particularly at lower IOPs.4
Rebound
These devices employ a small probe, sans anesthesia, that briefly contacts the cornea. They have slightly overestimated true IOP.5
One device enables patients to self-monitor IOP, capturing diurnal fluctuations that can go undetected in the clinic. A 2023 study validated its use for at-home glaucoma monitoring.6 (Incidentally, 2 continuous IOP-monitoring devices are also available.)
I recently had a normal tension glaucoma patient who was progressing despite office IOP’s in the low teens. This device showed their IOP increased significantly between 3 AM and 6 AM. I instituted more aggressive treatment.
Dynamic Contour (DCT)
This uses a contoured sensor tip to match the corneal shape, measuring IOP dynamically and independently of CCT.
Studies comparing DCT with intracameral manometry in cadaver and living eyes demonstrate strong correlation and minimal biomechanical influence.7
Valuable Insights
None of these devices per-fectly capture “true” IOP in every patient, but they do offer valuable insights that account for variables. The modern OD’s goal isn’t to replace Goldmann, it’s to integrate these complementary tools into their practices to refine diagnosis, personalize management, and, ultimately, improve glaucoma care. OM
References
1. McCafferty S, Levine J, Schwiegerling J, Enikov ET. Goldmann and error correcting tonometry prisms compared to intracameral pressure. BMC Ophthalmol. 2018;18(1):2. doi: 10.1186/s12886-017-0668-z. PMID: 29301514; PMCID: PMC5753488.
2. Zhang H, Sun Z, Li L, Sun R, Zhang H. Comparison of intraocular pressure measured by ocular response analyzer and Goldmann applanation tonometer after corneal refractive surgery: a systematic review and meta-analysis. BMC Ophthalmol. 2020;20(1):23. doi: 10.1186/s12886-019-1288-6. PMID: 31924174; PMCID: PMC6954592.
3. Zimprich L, Diedrich J, Bleeker A, Schweitzer JA. Corneal Hysteresis as a Biomarker of Glaucoma: Current Insights. Clin Ophthalmol. 2020;14:2255-2264. doi: 10.2147/OPTH.S236114. PMID: 32848355; PMCID: PMC7429407.
4. Frenkel RE, Hong YJ, Shin DH. Comparison of the Tono-Pen to the Goldmann applanation tonometer. Arch Ophthalmol. 1988 Jun;106(6):750-3. doi: 10.1001/archopht.1988.01060130820030. PMID: 3369998.
5. Ertel MK, Seibold LK, Patnaik JL, Kahook MY. Comparison of intraocular pressure readings with Perkins, Tonopen, iCare 200, and iCare Home to manometry in cadaveric eyes. Int J Ophthalmol. 2022 Dec 18;15(12):2022-2027. doi: 10.18240/ijo.2022.12.19. PMID: 36536963; PMCID: PMC9729075.
6. Quérat L, Chen E. iCare® Home vs Goldmann applanation tonometry: Agreement of methods and comparison of inter-observer variation at a tertiary eye centre. Eur J Ophthalmol. 2023 Jan;33(1):312-318. doi: 10.1177/11206721221099252. Epub 2022 May 3. PMID: 35505614; PMCID: PMC9834317.
7. Kniestedt C, Kanngiesser H, Stamper RL. Assessment of Pascal dynamic contour tonometer in monitoring IOP after LASIK. J Cataract Refract Surg. 2005;31(3):458-9. doi: 10.1016/j.jcrs.2005.02.021. PMID: 15811722.
