Fundus photography is no longer limited to table-top devices costing thousands of dollars. For remote screening, especially in regions where access to care is limited, smartphones are taking center stage with the help of clever adapters that can turn off-the-shelf phone cameras into fundus cameras.
A variety of smartphone adapters for fundus imaging are on the market—most are non-mydriatic, have slit lamp attachments and use an app to record, save and send images for grading and telehealth consultations. Some even have built-in artificial intelligence that can read fundus images and detect diabetic retinopathy.
The main issue physicians raise with handheld fundus cameras, and particularly smartphone-based cameras, is the difficulty in getting a clear image. Often, multiple photos are needed, and with a smaller field of view than a standard fundus camera, it may be more difficult to appreciate details. Experts say that smartphone-based imaging is best for screening purposes. And in less-advantaged regions, this is this precisely why care providers are using smartphone fundus cameras.
A recent study conducted in Samoa—which has one full-time ophthalmologist in the entire country—investigated the factors that impact inter-rater agreement of glaucoma suspect optic disc status with a low-cost, handheld, non-mydriatic fundus camera attached to an iPhone6.
In the study, a lay examiner obtained color fundus photos of 206 participants. The images were remotely graded by an ophthalmologist and an optometrist, and patients whose images were identified as at-risk for glaucoma were referred to a glaucoma subspecialist for review.
The researchers recorded fundus photo brightness, contrast and focus by measuring the cup, rim and temporal regions of the disc. They generated stereoscopic image pairs from a subset of individual non-mydriatic photographs.
The graders identified features suggestive of glaucoma based on optic disc cupping in 16% of patients. The researchers recorded a moderately strong agreement between graders (90.3%). Of the 16% of participants whose features were suggestive of glaucoma, 94% had clinical risk criteria for potential glaucoma when reviewed by the subspecialist.
Interestingly, the cup brightness in fundus photos was significantly associated with cup-to-disc grade, in which a brighter disc yielded a higher cup-to-disc ratio.
The researchers concluded that smartphone-based screening is a simple, low-cost method for measuring the cup-to-disc ratio of the optic nerve. They suggested combining this method with IOP measurements and other glaucoma risk factors when testing for glaucoma to help identify patients for referral.
LaMonica L, Bhardwaj MK, Hawley NL, et al. Remote screening for optic nerve cupping using smartphone-based non-mydriatic fundus photography. J Glaucoma. September 22, 2020. [Epub ahead of print].