Measurement of intraocular pressure (IOP) is the cornerstone of glaucoma management as IOP control remains the crux of glaucoma therapy.1 Several new and portable devices have been developed to measure IOP.2 These technologies have improved eye disease screening, diagnosis, and monitoring, particularly in remote and low-resource environments. There are now portable handheld tonometers that can be used in different positions for patient comfort and do not require anesthesia. They are practical for usage in a variety of clinical settings, including screening camps, operating theaters, and emergency rooms. Despite several advances and the introduction of many novel and portable devices, Goldmann applanation tonometry (GAT) (Haag-Streit, Koeniz, Switzerland, and other manufacturers), which is mounted on a slit lamp, remains the gold standard for IOP measurement.3 The Perkins tonometer (Haag-Streit, UK) is based on the same principle as GAT but does not require a slit lamp; thus, it is portable and can be used in any position. It requires instillation of a topical anesthesia and fluorescein dye for IOP measurement. Other commonly used portable tonometers include iCare (Icare Finland Oy, Vantaa, Finland) and Tono-Pen (Reichert Technologies, USA). The iCare tonometer is a contact rebound tonometer (spherical tip with a diameter of approximately 1.7 mm2, resulting in a contact area of about 4.6 mm2) which does not require anesthesia or fluorescein dye for IOP measurement and does not cause patient discomfort.4 When compared to most portable tonometers, the iCare tonometer has been reported to deliver IOP readings with good agreement to GAT. Its wide usage in community screening and drive-through clinics is particularly beneficial due to its portability and user-friendliness.2 The Tono-Pen combines principles of applanation and indentation to measure IOP. It can be used in any position and does not require special training or fluorescein dye. As it requires only a small contact area (0.79 mm2), it can be used in irregular corneas for IOP measurement. The disadvantage is that, when compared to GAT, it may overestimate or underestimate IOP depending upon the range of IOP in which it is tested. With advances in technology over the past few decades, there has been a significant increase in the development and production of portable slit-lamp systems, enabling detailed examination of the eye’s anterior segment.2,5,6 These can be used in conditions where a table-mounted slit-lamp examination is not feasible, such as for pediatric patients, bedridden patients, and uncooperative patients, or in settings where conventional table-mounted slit lamps are not available, like screening camps. However, these portable slit lamps do not have a facility to accommodate the GAT for measuring IOP.5,6 Therefore, other handheld devices, like the Perkins, iCare, or the Tonopen, may be needed for measuring IOP.7 This increases the number of devices required to cater to different settings and consequently the cost of care. A portable modular slit lamp (MSL)-mounted Goldmann applanation tonometer showing good agreement in IOP measurements with standard GAT and Perkins tonometry has now been developed.8 Compared to Perkins, it is cost-effective (easily 3D-printed) and can provide videographic recordings of the procedure. When the procedure is performed by a trainee ophthalmologist, the recordings may also be used as a teaching tool to check if the measurement is appropriately done. One major disadvantage of the MSL-mounted GAT may be that it cannot be used in patients in the supine position (due to a lack of counterbalance), limiting its use for examination under anesthesia and in bedridden patients. Further development of IOP measurements in the supine position may enhance its utility. Therefore, the use of portable devices offers great promise for reducing preventable vision loss worldwide and provides an efficient, scalable alternative for filling in gaps in eye care.
Mahalingam et al. (Wed,) studied this question.