Retinal imaging has advanced drastically during the past decade. With the advent of higher sensitivity imaging systems and more powerful software incorporation into present devices, knowing what is ideal or necessary for starting a practice can be a daunting task.

Optical coherence tomography (OCT), fundus photography, perimetry and ultrasonography machines are the primary requirements. The utility of these imaging systems often lies in their ability to diagnose and document findings that are not able to be observed using classic direct or indirect ophthalmoscopy. However, more diagnostically advanced modalities are available, including OCT-angiography (OCTA), ultra-wide field imaging (UWF), fundus autofluorescence (FAF), and fluorescein angiography/indocyanine green angiography (FA/ICG) combo machines, just to name a few.

The goal of this article is to give a baseline recommendation on which types of equipment to utilize in a practice to give you the most “bang for your buck” and how these technologies fit into diagnosing a variety of conditions.

TECHNOLOGY

OCT and fundus photography

The most utilized retinal imaging modality currently is OCT (Figure 1). Due to its advanced diagnostic capabilities, it has overtaken fundus photography in frequency of use — although by no means has it removed the necessity of a fundus camera in a clinic (Figure 2). With the importance of both diagnostic modalities in mind, a combination OCT and fundus photography device may be most functional for the practice. They provide ease of use and multiple imaging modalities, including fundus auto-fluorescence, while often sporting a lower price tag than obtaining the devices separately. Also, these machines can decrease the footprint requirement in a clinic with less space for imaging, making them great all-around starting pieces of equipment.

For a clinic participating in a higher volume of OCTs and/or fundus photos, it may be beneficial to obtain separate imaging systems. In addition to the increased number of patients imaged, separate OCT and fundus cameras often obtain higher quality images and have more associated capabilities, such as combo FA/ICG, widefield imaging or OCTA. Standalone OCT systems may come with a higher price tag, but they provide increased quality scans with many having the ability to perform OCTA, although this imaging capability is not completely necessary in the general ophthalmologist’s office and its utility is directly correlated to the physician’s familiarity and training.

More expensive, standalone fundus cameras are often capable of providing imaging through a non-mydriatic pupil, and some can even obtain widefield images in this manner. This grants a complete examination of the retina and can be incorporated easily into a patient’s visit without the need to dilate, expediting annual exams while characterizing and recording disease entities readily. In the standalone cameras requiring dilation, images are frequently of increased quality and many are also able to perform FA, which remains the gold standard in retinal imaging for diabetic retinopathy and macular degeneration.

Ultrasonography

The next important device in the diagnostic toolbox is ultrasonography. While some handheld devices work in correlation with a smartphone and claim to have “ophthalmic” settings, the quality of imaging is often not high enough to be diagnostic. Therefore, it is recommended to obtain a dedicated ophthalmic B-scan system, which often includes A-scan and pachymetry components as well. The primary utility of retinal ultrasonography lies in diagnosing conditions such as retinal detachment, vitreous hemorrhage, dislocated lens and posterior scleritis. There are a variety of similar products in this market, with equivocal diagnostic capabilities, so the user interface and ease of saving imaging are essential to consider. For example, printing on thermal paper is much less utilitarian in this digital world.

Perimetry

The final necessary piece of diagnostic machine is a perimetry machine. The most commonly utilized devices perform the Humphrey visual field test, mapping up to 30 degrees nasally and temporally, and are imperative when monitoring patients for glaucoma progression or neurological field defects. Many models are available for microperimetry, but these only map the central visual field and are not diagnostic for these pathologies.

UTILITY

Overview

In diagnosing and monitoring progression of certain retinal pathologies in their earlier disease states, these imaging systems allow us to obtain a more positive prognosis.

Some of the retinal conditions most applicable to this idea are diabetic retinopathy, macular degeneration, hypertensive retinopathy and glaucoma. These conditions most frequently present on a spectrum, beginning as asymptomatic findings on exam prior to being readily noticed by patients. While in this stage, utilization of screening modalities such as OCT, FAF, widefield imaging and perimetry as adjuncts to examination, may allow earlier diagnosis and treatment.

Diabetic Retinopathy

Diabetic retinopathy is often asymmetric in presentation and most readily documented via combination widefield fundus photography and OCT. As it progresses, FA can prove useful in demonstrating the extent of disease and demonstrating areas of neovascularization and proliferation. It is advisable to examine an asymptomatic diabetic patient annually while encouraging A1C control with a goal of less than 7.0%. Any early findings (ie, dot/blot hemorrhages, microaneurysms and exudate) observed using these imaging modalities can be the first sign of disease and an indication to stress blood sugar control to a patient in combination with informing their primary care physician (PCP) and/or endocrinologist.

Hypertensive retinopathy

Hypertensive retinopathy is most readily observed in its asymptomatic stage via fundus photography. Observance and documentation of cotton wool spots, infarctions in the retinal nerve fiber layer, are early indicators to the necessity of improved blood pressure control or hypertensive workup with a patient’s PCP. Catching it in this stage is ideal before more severe and debilitating conditions such as retinal vein occlusion develop, which often result in permanent vision loss and need for intraocular injections.

Glaucoma

Glaucoma is often monitored and diagnosed via IOP measurements in combination with optic nerve exam, but the supplement of pachymetry, OCT of the retinal nerve fiber layer and perimetry, are necessary in monitoring its progression and isolating specific patients with normal tension glaucoma.

Macular degeneration

Macular degeneration can be most easily identified and monitored utilizing a combination of FAF imaging and OCT in patients with macular pigmentary changes and drusen observed on exam. When early dry degeneration is observed, it is recommended to prescribe patients Age-Related Eye Disease Study, or AREDS, vitamins and monitor every 6 months for progression. In addition, instruction to utilize an Amsler grid each day at home while in the asymptomatic state can detect any early changes if transition to wet disease occurs.

As the disease progresses, FA and ICG can be utilized to diagnose transition to wet disease while assisting in potential laser treatment or distinguishing from other disease processes such as polypoidal vasculopathy and central serous retinopathy. While only about 10% of patients will make this conversion, the process may be rapid and quickly lead to reduced visual potential if not diagnosed and managed quickly.

CONCLUSION

Using these imaging modalities, a wide variety of retinal pathologies can be elucidated and managed effectively. While it is not economically feasible for every practice to obtain top of the line models, having a device for each of these four imaging modalities is highly recommended for proper management of retinal conditions. OM

Luke Mein, MD is a graduate of the Long School of Medicine in San Antonio, Texas, and works as a clinical research coordinator at Medical Center Ophthalmology Associates in San Antonio, Texas.

Michael Singer, MD, is clinical professor of ophthalmology at the University of Texas Health Science Center in San Antonio, Texas, and the director of clinical research at Medical Center Ophthalmology in South Texas. In 2018, he was inducted into the Retina Hall of Fame.

Disclosures: Dr. Singer reported relationships with Aerie, Allegro, Allergan, DRCR, Eyepoint, Genentech, Icon, Ionis, Kalvista, Kodiak, Mallinckrodt, Novartis, Opthea, Optos, Regeneron, Santen, Senju, Spark and Sydnexis.