Optimizing fundus visualization is a long-standing goal of ophthalmic care. Since its inception, physicians have relied on the art of indirect ophthalmoscopy (IO) to identify and treat difficult to visualize peripheral pathologies. Generations of ophthalmologists have mastered this technology to optimize patient care, but even the most well-trained is liable to miss pathology, especially in patients with limited mydriatic pupil size. Thus, the development and improvement in fundus photography has been imperative to proper management of retinal pathologies.
In response, the industry has created cameras to visualize wider fields of view, expanding from the original 10° to some systems now visualizing up to 200° of retina in a single image, ~82% of the entire retinal surface. This article will cover the progression specifically of widefield fundus imaging modalities, the different imaging modalities capable of each and the diseases most frequently imaged.
Fundus photography in the modern era has consisted of imaging systems capable of visualizing between 30° to 45° of the retina. Widefield imaging systems are defined as having the capability to visualize 50° or more, while the Diabetic Retinopathy Clinical Research Network, a renowned research and imaging organization, defines ultra-widefield (UWF) imaging systems as capable of capturing single images greater than 100° of visualization. These widefield images are obtained via a variety of techniques based on the camera but include primarily four visualization modalities: direct optics-based, contact lens based, confocal scanning laser ophthalmoscopy and broad line fundus imaging.
These imaging systems are capable of different modalities, each beneficial in identifying certain pathologies, to include UWF color fundus photography, fundus autofluorescence (FAF), fluorescein angiography (FA) and indocyanine green angiography (ICG). Additionally, some of the imaging systems are now capable of performing simultaneous optical coherence tomography (OCT).
Available UWF devices
Optos currently has four devices: California, Daytona, Monaco and Silverstone. The most advanced of these, the Silverstone, has color, red-free, choroidal, FAF, FA/ICG and concurrent swept-source OCT capabilities. The Monaco contains the photographic and OCT modalities. Additionally, with the auto-montage function, all these cameras can produce images providing 220° of visualization, or ~97% of the retina.
The California rg provides similar photographic modalities (color, red-free, choroidal, and AF), with the California fa including UWF-FA and the California icg including UWF-FA/ICG. Finally, the Daytona, provides similar imaging capabilities as the California rg but in a more compact, patient-friendly system.
Heidelberg currently offers three devices for retinal imaging: Spectralis OCT, Spectralis HRA+OCT and Spectralis HRA. With the use of a non-contact lens, all models are capable of fundus and infrared photography up to 105°. The OCT models are capable of macular, nerve and anterior OCT as well as macular OCT angiography. The HRA models provide FA/ICG modalities. Of note, with the use of the contact Staurenghi lens, it is possible to obtain images up to 150°.
Zeiss currently has two devices available: Clarus 500 and Clarus 700. These provide true-color imaging using “broad line fundus imaging” with modalities such as full color, red/green/blue free, FAF and external photography. Additionally, the Clarus 700 is capable of UWF-FA. Both devices capture 133° images and are capable of montaging images up to 200°.
Natus’ Retcam Envision is a fundus camera primarily focused on pediatric ocular imaging. As a mobile device with hand-held camera designed for patients in a supine position, this device varies greatly from the other cameras on the market. It can take 130° color fundus images and can perform UWF-FA as well.
In the clinic and in clinical trials
These UWF imaging systems are most useful in identifying pathology in the far periphery of the retina including but not limited to: diabetic retinopathy (DR), retinal vascular occlusion, uveitis, retinal breaks/detachments, ocular tumors and pediatric diseases. They additionally provide a potential corollary in future clinical research protocols, which currently rely on a seven-photograph montage resulting in visualization of 90° of the posterior pole — around 30% of the retina.
As well as improving methods of diagnosis and treatment in an ophthalmology setting, the increased implementation of these devices in optometry clinics can improve early identification and appropriate referral for evaluation of asymptomatic retinal pathologies.
DR is an extremely prevalent cause of visual deterioration, especially in underserved populations. Early detection of its severity can lead to prompt referral and treatment. While standard fundus photography can identify central pathology, including neovascularization of the disc and tractional retinal detachments, Ashraf et al published data in 2021 demonstrating that UWF imaging, especially UWF-FA, is superior in its quantification of ischemic disease secondary to capillary non-perfusion, as well as peripheral signs including pre-retinal hemorrhage and neovascularization elsewhere (NVE) (Figure 1). Both NVE and increased non-perfusion suggest an advanced disease state requiring more aggressive treatment.
Retinal vascular occlusion
Occlusion of retinal vasculature, both retinal vein occlusion (RVO) and retinal artery occlusion (RAO), can occur in any segment of the retina from the central vein/artery all the way to the periphery. Traditional fundus photography can visualize central occlusions, while UWF images can provide detection of occlusions occurring further in the periphery. These are less likely to be immediately visually significant but can identify the risk-state of the patient for future, more serious events such as central occlusion or angiogenesis and subsequent hemorrhage.
In the event of a peripheral RVO, the patient’s blood pressure control can be stressed. In the case of peripheral RAO, a systemic cardiovascular workup may be required to prevent complications such as central retinal artery occlusion or stroke.
ULTRA-WIDEFIELD IN THE PRACTICE
In implementing a widefield camera in a general ophthalmologist clinic, it is possible for patients to receive a full examination without being dilated, improving patient experience while maintaining efficacy. Devices are generally easy to use, both for staff and patients, and staff can be trained to capture images in a short period of time.
More experience is required to perform FA/ICG studies, but with supervised training by an experienced operator, even this skill can be acquired in a relatively short period of time by a photographer proficient with the camera. The process of taking fundus images, even multiple modalities such as color and AF at the same visit, is relatively quick at around 5 minutes for a cooperative patient with an experienced operator, and it promotes smooth clinic flow even with frequent use.
Of note, a patient with low vision (count fingers or worse) or limited physical mobility can be more difficult to image and require more time. When performing FA and/or ICG, the informed consent process, preparation of the dye, and obtaining vascular access, in addition to length of the test (usually between 5-10 minutes once begun), can require around 30 minutes total; so, these should be scheduled accordingly.
In terms of billing, fundus photos cannot be billed on the same visit as either IO or OCT testing. However, if paired appropriately with intermediate or comprehensive exams, they are compensated at a rate similar to IO. Images obtained from these devices can frequently be integrated into the existing patient EMR or reviewed using a stand-alone software, allowing for access and visualization with the patient in the room during examination.
This is beneficial in patient education and understanding their condition as well as its potential progression or improvement.
The posterior inflammatory state of the eye is usually diagnosed with slit lamp and OCT criteria, including presence of cells in the vitreous and swelling of the central macula. However, UWF-FA can demonstrate the level of peripheral vascular leakage, allowing prognostication of the severity of inflammation and guiding treatment accordingly.
While IO with scleral depression remains the primary method of evaluating mechanical retinal pathologies, UWF imaging, especially in optometry settings, can be used to identify and treat early retinal breaks before they progress to detachment. Additionally, if retinoschisis or detachment is present, UWF imaging can track progression and identify any potential breaks requiring treatment (Figure 2).
FIGURE 2. Color fundus photo of an eye with retinal detachment
The primary posterior tumor that is most frequently diagnosed is the uveal melanoma. Traditionally arising from a nevus present, it is very serious, so early identification and treatment are essential. With UWF imaging, peripheral pigmentary changes are more readily identified and easily tracked, correlating to earlier diagnosis and evaluation of potentially cancerous lesions.
Many pediatric conditions can be identified using widefield imaging, including retinoblastoma, Coats’ disease, retinopathy of prematurity, inherited retinal dystrophies and familial exudative vitreoretinopathy. Effective IO of young children can be difficult due to cooperation, sometimes requiring sedation to perform, so UWF imaging can enhance sensitivity of diagnosis and ensure early treatment as well as avoid risks associated with sedation.
IMPROVING DETECTION AND THE PATIENT EXPERIENCE
Advances in fundus imaging have greatly improved the identification of retinal pathologies, enabling physicians to accurately track progression of disease states outside of hand-drawn images. Improved platforms are providing increasingly detailed and extensive diagnostic images.
Patients benefit as well thanks to ease of image capture, positioning and required pupil size, as many of these systems can perform on non-mydriatic eyes.
With UWF imaging, the future of fundus photography is bright. OM