Fundus photography is essential in the diagnosis and monitoring of various ophthalmic diseases. Besides the obvious of being able to share these photographs with specialists at other locations and/or times, they can also magnify areas of interest that cannot be easily seen with a handheld ophthalmoscope. Images are viewed in real time and can be used to discuss disease processes with patients. As well, many are non-mydriatic, so can be used in the non-dilated pupil, saving time in the clinic and eliminating inconvenient factors related to a dilated pupil. There is also great potential for advances in telemedicine using digital imaging.
Tyler et al. wrote an article in 2000 characterizing digital fundus camera systems and compared them to film cameras. A digital sensor can attain much higher efficiency than film, which is limited to just a few percent. A concern at the time was that tonal quality of color retinal photographs might be difficult to control in digital fundus camera systems, but modern technology has made advances over the past decade to overcome some of these shortcomings in the silicon photo sensors that they used to contain.
A fundus camera provides an upright, magnified view of the fundus. A typical camera views 30 to 50 degrees of retinal area, magnifies 2.5x, and can be modified with zoom or auxiliary lenses. Below are listed a few of the digital fundus cameras available.
Canon: Canon makes mydriatic and non-mydriatic retinal cameras, as well as hybrid cameras encompassing both technologies (CX-1). The company’s CR-2 PLUS digital non-mydriatic retinal camera has the ability to perform color and fundus autofluorescence photography that can be used to detect macular residue that gathers in the retinal pigment epithelial layer. This system can image patients with pupils as small as 3.3mm in a small pupil mode. The CR-2 PLUS has a dedicated camera, which incorporates a high definition CMOS sensor with 18 megapixels.
Nidek: This company recently released the Automated Fundus AFC-330 Camera, a non-mydriatic camera. Features include a 8.4” tilting color touchscreen, an AutoAlign and AutoTrack detection mechanism to follow patient movements, the ability to obtain panoramic images of seven fields with automatic fixation adjustments, AutoShot to capture photos during optimal conditions, and automatic pupil measurement and a small pupil mode. This system communicates via LAN without the need for an external PC in the screening area.
i-Optics: The new EasyScan was released in the US about a year ago. It is a lightweight 7kg unit making it portable. There is a USB connection for ease of data sharing and archiving. The new v1.3 features autocapture, ultra flexible workflow and easy image comparison. EasyScan is based on confocal Scanning Laser Ophthalmoscope (SLO) technology. It can image through pupils as small as 2mm.
Zeiss: VISUCAM PRO NM is a non-mydriatic fundus camera system designed for routine clinical use and screening. It integrates image capture to image documentation and can get through a pupil as small as 3.3mm. Images immediately appear on the 17” flat screen monitor and are automatically stored. 3D images and 45 and 30-degree field angles are features.
Kowa Optimed: The non-mydriatic Alpha-D digital fundus camera can shoot through a pupil as small as 3.7mm and is compatible with most PC-based office systems. This compact system has 3 internal fixation targets so you can take a single central or peripheral retinal photo or a stereo photo. A wider view is obtained with the 45-degree angle function and a more detailed view uses the 20-degree setting. Alpha-D accommodates patient refractive errors and features a large external LCD monitor and high-resolution camera. There are different megapixel resolution charge coupling device cameras (2.1 and 6) that can be used with this instrument.
Centervue: The DRS is a non-mydriatic digital fundus camera that supports single or multi-field acquisition protocols. It provides 7 different 45-degree fields and can get through a 4.0mm pupil. The unit self-aligns to the target eye by sensing the patient, focuses the retina, adjusts level and captures the image in less than 30 seconds. The camera is completely automatic and has a sensor resolution of 48 pixels/deg.
CSO: Cobra is a non-mydriatic fundus digital camera providing a field of view of 65 x 45 degrees. Cobra uses a high-resolution camera and IR illumination for alignment and capture to display the subretinal layer and retinal image capture. It operates through a pupil as small as 2.2mm and a room with standard lighting conditions. This unit is available through Designs for Vision.
One can always convert an existing fundus camera to a fully-digital system by use of adapters or by connecting with software such as Merge Eye Station, an image capture software and digital interface with solutions up to 21 megapixels. Related to digital fundus cameras is the following software program that links patient information among different providers so patients can be screened and followed with little effort.
EyePACS: This program is designed for primary clinic personnel (nursing, technical, or administrative staff) who are trained and certified by the EyePACS program to acquire retinal images from standard digital retinal cameras. Clinical data and 8 high-resolution images per patient (2 external and 6 retinal) are encrypted and transmitted to a secure Internet server, using a standard computer and Web browser. This software has allowed primary care providers to share files and screen retinopathy patients.
Advances in digital fundus camera technology continue. No doubt more and more systems will become available with even higher resolution, faster picture taking and more ergonomic design. With all of the advantages of digital photography, it will be rare to find film in a practice.