Ophthalmic imaging is an essential component of ocular disease diagnosis, monitoring, and management. Most forms of ophthalmic imaging fundamentally involve microscopy coupled with a means to record the formed images on film or, more commonly today, digital sensors (Fig. 1). Ocular imaging represents the standard of care for managing glaucoma, diabetic retinopathy, and numerous other internal and external ocular conditions. Digital imaging is emerging as the standard of care for conditions where subjective clinical grading is not sufficient, such as dry eye management and infrared meibography or corneal scarring and staining. Modern digital imaging systems have enhanced the ability to acquire high-resolution images, streamlined interpretation by eliminating the need for film processing, and enhanced our capabilities for quantitative analysis of the images captured. With that flood of data has come the challenge to manage and interpret image data. Although the use of imaging technology in patient care and clinical research has flourished, evidence-based use of the resulting data has lagged and is a rich opportunity for clinical investigators.
FIGURE 1:Confocal microscopy image of primate lens epithelial cells along suture line.
Ocular photography is the most established and reliable form of imaging, and part of its enduring value comes from the stability of this technology. Patients with disc photographs taken in the 1960s can still benefit from those images today. Modern camera systems allow for spectral analysis, automated focus, image optimizations, and registration of images from previous examinations. As ocular imaging has become more sophisticated, photography remains valuable.
Many members of our society (or in some cases, their staff) are excellent and accomplished ocular photographers. Since 2015, the American Academy of Optometry has recognized excellence in ocular photography through an annual contest. Each year, the best retinal and anterior segment eye photographs were awarded and recognized for their achievements. Images from 2015 to now are hosted on the Academy's Web site and can be found here: https://academymeeting.org/optometry-meeting-information/2020-ocular-photo-contest-winners/. Please have a look at these outstanding images created by expert ocular photographers from around the globe. Their work is truly impressive and demonstrates the intersection of art, science, and clinical anatomy.
In 1991, optical coherence tomography was first described and since then has become the most dominant form of ophthalmic imaging used in clinical practice.1,2 Optical coherence tomography imaging is, in essence, a form of confocal microscopy combined with low-coherence interferometry. This technology has evolved rapidly owing to its safety and its ability to provide histological resolution in the living eye. This capability is critical for detecting retinal structural abnormalities such as macular edema and can be far more sensitive than other clinical techniques, making retinal optical coherence tomography the recognized standard for detection of diabetic macular edema.3
Whereas optical coherence tomography imaging has grown in use, retinal fluorescein angiography and Indocyanine Green Angiography have fallen. Recent estimates of optical coherence tomography use in clinical practice range between 60 and 70% among retinal specialty practices with continued growth.1 Over the past 5 to 7 years, optical coherence tomography angiography has been growing in adoption despite its many challenges related to image quality, prolonged image capture, susceptibility to eye motion artifacts, and no accepted standards for quantification or interpretation of the resulting image data. Nevertheless, the allure of retinal angiography that does not require fluorescein injections and permits quantitative analysis of retinal vascular structure is very attractive. Given time, the challenges of imaging retinal microvascular dynamics will likely be overcome, resulting in greater adoption.
Coupling optical coherence tomography imaging with other modes of structural and functional assessment of the eye and visual system will bring other possibilities for the clinical evaluation of ocular disease conditions. Although there are commercial instruments for combined optical coherence tomography/electroretinography evaluation in animal models of eye disease,4 such systems are not yet in clinical use for humans. Others have combined optical coherence tomography imaging with micromechanical stimulation for testing ocular biomechanics.5
Adaptive optics is another established technology for ophthalmic imaging with numerous clinical applications that are now emerging. Early uses of adaptive optics for ocular imaging involved studies of retinal architecture and permitted unprecedented views of retinal structure.6 Most recently, others have followed with applications for glaucoma imaging of the lamina cribrosa7 and more recently the trabecular meshwork.8 Using novel approaches that enable high-speed, high-resolution scanning, combined with retinal image stabilization, Gu and colleagues9 have quantified the speed of individual erythrocytes as they flow through retinal capillaries. Another application of adaptive optics combines programmable imaging systems to probe the neural and sensory effects resulting from optical aberration structures.10
There are tremendous advances happening in optics and biophysics that will continue to produce a steady stream of clinical imaging innovations. Although these imaging capabilities will undoubtedly expand, this will then lead to an ongoing demand for clinical research to assess their value and establish the evidence needed to determine the clinical utility and efficacy of these innovations.