There are a variety of different methods available to visualize the retina, including ophthalmoscopy, ocular coherence tomography, and fluorescein angiography. Each of these methods has its own advantages and disadvantages, and often they are used in conjunction with one another to provide ophthalmologists with vital information required for diagnosis, monitoring, and treatment of a variety of ocular conditions. Below, each of these retinal imaging techniques will be discussed in further detail.
Ophthalmoscopy (also called ‘fundoscopy’) involves the direct visualization of the retina by an ophthalmologist using a light source. There are generally two types of techniques for achieving this: direct ophthalmoscopy (which uses a small handheld lens with light source [image below]) and indirect ophthalmoscopy (which uses a head-mounted light and hand-held lens). Though each of these methods has certain advantages over the other, in most cases either can be used to effectively image the retina. Compared to other imaging techniques, ophthalmoscopy is relatively quick and requires the least high-tech equipment. For this reason, ophthalmoscopy is part of a routine ophthalmologic exam. However, only a gross anatomical image is provided. This can often be sufficient to diagnose and monitor much retinal pathology, but if greater detail is required, one of the other imaging techniques may need to be employed.
Ocular Coherence Tomography
Ocular Coherence Tomography (OCT) is special imaging technique ophthalmologists can use to visualize the retina. Similar to how an ultrasound uses reflected sound waves to produce an image, OCT uses reflected infrared light to reconstruct the 3-dimensional structure of the retina with exceptional resolution. By being able to visualize the retina in this way, OCT provides ophthalmologists with images they can use to diagnose many conditions, including macular degeneration, glaucoma, and diabetic retinopathy. The procedure involves directing light in the near-infrared spectrum at the retina, and measuring the small portion of light that is reflected back from the various layers of the retina. By doing this, the OCT machine can differentiate between the different layers of the retina and construct a representative image, with a resolution in the range of micrometers! As OCT is fast (no patient preparation required) and risk-free (no ionizing radiation is involved), it is a technology that has become popular within the ophthalmology community.
Fluorescein Angiography is an imaging technique used to visualize the vessels of the retina. The procedure involves the injection of a special dye, fluorescein, to help ophthalmologists see the organization of blood vessels within the eye. This can be useful in monitoring a number of conditions, including diabetes and retinal vein occlusions. The procedure itself is relatively simple. First, medications are used to dilate the pupil and initial images of the retina are taken. Then the patient is given an injection (generally in to the arm) of fluorescein dye, which will travel through the circulation to the vessels of the eye. By taking a number of images at various times after injection, an ophthalmologist is able to visualize the circulation within the eye and determine if there are any abnormalities. By being able to identify aberrations or dysfunction of the retinal vessels, ophthalmologists are better able to determine the most appropriate course of treatment for a number of chronic conditions.Evan Martow