**1. Introduction**

Glaucoma is a progressive disease of the optic nerve and a leading cause of irreversible vision loss. Globally, in 2013, the prevalence of glaucoma was 3.54% among people aged 40–80, affecting 64.3 million [1]. It was estimated that by 2040, this number will increase to 111.8 million [1]. The demand for ophthalmologists to take care of glaucoma patients is expected to exceed the supply. In 2018, the Association of American Medical Colleges (AAMC) forecasted that there will be worsening shortages of physicians in the United States, with an estimated shortfall of 33,800 to 72,700 specialists by 2030 [2]. The report did not state what the estimated shortfall of ophthalmologists will be per se, but the trend is expected to be similar. The reasons for this shortfall include the stagnant number of ophthalmology residency and glaucoma fellowship positions, the increasing number of retiring ophthalmologists, and the aging population. In order to ensure adequate care for the increasing population of glaucoma patients, each ophthalmologist will have to accommodate a greater number of patients, eventually leading to overbooked clinic schedules, long wait times for patients, and crowded waiting rooms. The increasingly long wait times for the next available appointment can be detrimental to patient care. New strategies, such as the use of telehealth, will be increasingly important to limit clinic visits to patients who absolutely need to be seen, without compromising the care of patients with a stable disease.

Telehealth, as defined by Merriam-Webster, is health care provided remotely to a patient in a separate location using a two-way voice and visual communication. A computer or smartphone is needed to establish this communication. Because of the coronavirus disease 2019 (COVID-19) pandemic, the use of telehealth has accelerated due to patients' fear of contracting COVID-19 and the reduced number of in-person appointments given. Telehealth has also provided a convenient way for people living in rural regions to access their doctors.

There are three main purposes of telehealth in the field of glaucoma. One, is to screen for patients who have glaucoma, or are glaucoma suspects (i.e., those who have optic nerve appearances suspicious but not definitive for glaucoma). Two, for those newly diagnosed

**Citation:** Wong, S.H.; Tsai, J.C. Telehealth and Screening Strategies in the Diagnosis and Management of Glaucoma. *J. Clin. Med.* **2021**, *10*, 3452. https://doi.org/10.3390/jcm10163452

Academic Editor: Miriam Kolko

Received: 6 July 2021 Accepted: 2 August 2021 Published: 4 August 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

with glaucoma, to determine the severity of the disease and treatment plan. Three, for those diagnosed in the past, to monitor for disease progression and change management as needed. Each purpose requires a different set of equipment, as discussed below.

## **2. Equipment**

#### *2.1. Visual Acuity Test*

Visual acuity is checked conventionally with a Snellen chart of letters placed 20 feet or 6 m away. If the patient has a refractive error, one should wear glasses corrected for distance. For each eye, the visual acuity of the smallest line the patient can read (at least half the letters correctly) is recorded. For the patient to perform this at home, one can either purchase a Snellen chart and hang it 20 feet away, print out a Snellen chart online and follow its instructions, or use a smartphone app. Of note, small Snellen charts, such as those on the smartphone, are referenced at reading distance, and would require presbyopic patients (typically those age 40 or above) to wear their reading glasses. A literature review [3] of mobile vision acuity applications revealed that the Peek Acuity application (Peek Vision Ltd., Berkhamsted, England) performed best, with a test–retest variability of ±0.029 Logarithm of the Minimum Angle of Resolution (LogMAR) for 95% confidence interval limits and a mean difference of 0.055 LogMAR when compared with visual acuity measured in clinic.

### *2.2. Intraocular Pressure Measurement*

Knowing the intraocular pressure (IOP) is crucial for the diagnosis and management of glaucoma. The Early Manifest Glaucoma Trial (EMGT) demonstrated that reducing the IOP by 25% lowered the risk of glaucoma progression by 50% over 6 years [4]. Measuring IOP via telehealth is a challenge because measurement requires the instillation of an anesthetic eye drop with fluorescein and the use of a Goldmann applanator attached to a slit lamp, which is equipment that can only be used in the clinic by a skilled technician or physician. Portable IOP measuring devices with reasonable accuracy are available for use. In the setting of a glaucoma screening outside of clinic, the Tono-Pen®, the Pulsair Air Puff tonometer, the iCare rebound tonometer, the Ocular Response Analyzer, and the Diaton transpalpebral tonometer are suitable devices that technicians can use. At home, patients can rely on the iCare HOME. Intraocular sensors such as the Eyemate® and Injectsense can provide IOP data throughout the day as well. If no equipment is available, the IOP range can be estimated by palpation.
