*2.3. Anterior Segment Photography*

Although photography does not offer as much clarity as an in-person examination on the slit lamp, it can provide important information relevant to the diagnosis of the type of glaucoma and to monitor for postoperative complications. For example, the camera may capture the presence of white material along with pupillary margin, indicative of pseudoexfoliation, or an opacity within the pupil, indicative of a dense cataract.

In the setting of a screening program where a slit lamp is not available, a digital single-lens reflex camera (DSLR) with maximum zoom can be used to capture images. For those who had glaucoma surgery, of which the surgical site is in the superior or inferior conjunctiva, the technician would need to shift the eyelid away and have the patient look at the opposite direction to capture images of these areas. The advantages of the DSLR camera include its high resolution, wide range of magnification, and the ability to adjust the flash intensity. Tweaking the settings allow for high quality images of the anterior segment. It has even been demonstrated that when a DSLR camera's infrared-blocking filter is replaced with a piece of glass, iris transillumination defects of the iris can be photographed clearly [44].

At home, a cell phone camera can be used to capture a gross image of the eye, but the resolution and magnification are not high enough to visualize the anterior chamber. A smartphone adapter attached over the camera is needed for adequate magnification and near focusing in order to obtain clinically useful images. One such adapter is the Paxos Scope (DigiSight Technologies; San Francisco, CA, USA) which was found to be easy to use and was able to image a variety of anterior segment pathologies [45].

#### *2.4. Iridocorneal Angle Imaging*

To identify whether a patient is at risk for angle closure glaucoma, the ophthalmologist performs an examination technique called gonioscopy, in which a lens with side mirrors is placed on the cornea. The mirrors allow for the visualization of the anterior chamber angle, which contains the trabecular meshwork, the start of the aqueous humor's drainage pathway. When a large part of the trabecular meshwork is not visible due to the steepening of the iris, the patient is considered high risk for angle closure, and peripheral laser iridotomy is recommended.

In a setting where an ophthalmologist is not present to perform the gonioscopy, an anterior segment optical coherence tomography (ASOCT) can be used to measure the iridocorneal angle. Optical coherence tomography (OCT) uses near-infrared light to capture a high-resolution cross-sectional image of biologic tissue by the principal of interferometry. ASOCT parameters associated with angle closure include smaller anterior chamber dimensions (width, area, and volume) [46,47], a greater iris thickness and area [48], and a larger lens vault [49,50]. A regression model consisting of these parameters can

diagnose angle closure with an area under the receiver operating characteristic curve (AUC) > 0.95 [51]. A validated scoring system can be incorporated into the ASOCT image analysis software to identify eyes with angle closure [52]. If a suspiciously narrow iridocorneal angle is seen in a screening program, pharmacologic pupillary dilation should be deferred (as dilation can induce acute angle closure glaucoma) and the patient should be sent to an ophthalmologist for a gonioscopy to verify the diagnosis. Of note, ASOCT is a desktop device that is not portable and is only available in the clinic setting.

Ultrasound biomicroscopy (UBM) uses a high frequency transducer (35–100 MHz) to obtain high resolution images of the anterior segment and measurements of the anterior chamber depth, angle, and the lens vault. Compared with the ASOCT, UBM has a greater penetration range, allowing for the visualization of the ciliary body. This increased range is particularly useful to visualize the plateau iris, cyclodialysis cleft, anterior choroidal effusions, or any masses beneath the iris. The disadvantage of the UBM is a transmission medium, such as a bag of fluid or gel, between the ultrasound probe and the eye is needed. In order to obtain clinically useful images, the technician needs to be well-trained.

A direct visualization of the iridocorneal angle can be performed using a gonioscopy camera. The Gonioscope GS-1 (NIDEK; Gamagori, Japan) is a desktop device that acquires 360-degree color photographs of the angle. The patient's eye is anesthetized and coated with gel, and the device's attached 16-mirror gonioprism contacts the cornea. The system then automatically captures images at different focus points from each gonioprism mirror; it takes approximately 1.5 min to photograph both eyes. Images in focus are then selected and a 360-degree fused panoramic image of the angle can be generated. A more portable gonioscope is the EyeCam (Clarity Medical Systems; Pleasanton, CA, USA), which consists of a handheld camera that can be used to visualize the angle when the probe is held against the eye coated with a coupling gel [53]. The Nanyang Technological University and Singapore Eye Research Institute similarly developed the GonioPEN, a smaller pen-like probe that can obtain images of the angle [54].

#### *2.5. Fundus Photography*

When evaluating a patient for glaucoma, being able to visualize the optic nerve head is key. Traditionally, photographs of the optic nerve head can only be taken with a desktop camera after the pupil is pharmacologically dilated. In recent years, handheld cameras have been developed that can take fundus photographs, even without dilation. In addition to glaucomatous nerve damage, these cameras allow for the diagnosis of macular pathology and other retinal diseases as well. The portable fundus cameras on the market include the Pictor Prestige (Volk; Mentor, OH, USA), VISUSCOUT® 100 (Zeiss; Oberkochen, Germany), SIGNAL (Topcon; Tokyo, Japan), and VERSACAMTM α (NIDEK; Tokyo, Japan). They are generally gun-shaped with a base charger, weighs approximately 1 pound, has a 40 to 50-degree fundus angle of view (with a pupil at least 3 mm in diameter), has autofocus or manual focus modes, has a touchscreen that displays the photograph taken, and has Wi-Fi connectivity to send images online.

An alternative to using the fundus camera is to rely on a smartphone camera attachment. The D-Eye Retinal Camera (D-EYE Srl, Padova, Italy) is an attachment that can obtain images of the optic nerve, even without pupillary dilation. The camera attachment requires the smartphone to be as close to the eye as possible, and the smartphone's video mode is turned on so that the split-second frame of which the optic nerve is centered within the field of view and is in focus is captured. This method of obtaining optic nerve photographs requires practice and an adequately large undilated pupil. The image resolution is limited by the smartphone camera. A prospective study demonstrated that vertical cup/disc ratios graded from D-Eye smartphone ophthalmoscopy agreed with those from slit lamp examination in 72.4% of primary open angle glaucoma patients and 66.7% of ocular hypertension patients [55]. Another study revealed that pharmacologic pupillary dilation improved D-Eye's vertical cup/disc ratio measurement significantly [56].
