The specular microscope allows viewing of objects illuminated from the same side as the observation system. Thus, the objective lens also acts as the condenser lens. Light passes from inside the microscope out through the objective lens to arrive at a focus near the focal plane of the lens. If this position coincides with a reflecting surface then the focused light is reflected back through the objective lens and is viewed through the eyepiece of the microscope. The first specular microscopes used for ophthalmic research were utilized by David Maurice in the 1960s in his work investigating corneal function. This technique enabled high-magnification images of both the epithelium and endothelium to be made, which had previously been difficult due to their transparency.
Early versions of the specular microscope used a contact dipping cone objective lens that was optically coupled to the cornea to provide higher magnification and resolution; however, most modern clinical specular microscopes can achieve equally high magnification without the need for ocular contact
These instruments are primarily used to view and photograph the corneal endothelium and to monitor its morphology. By direct viewing with the specular microscope, an overall impression of the condition of the endothelium can be established immediately. In addition, some of these instruments allow corneal thickness to be determined by measuring the distance between the epithelium and endothelium.
A specular microscope enables the viewer to study the morphology of the cells to look for any abnormalities indicating trauma. This type of microscope is helpful when identifying ocular conditions, such as Glaucoma, Fuch’s Dystrophy and Uveitis. Specular microscopy is also helpful for cataract patients and corneal transplant patients. Cell counts can help identify whether a patient’s cornea is at risk and enable a physician to identify potential risks pre and post-operatively.
Some specular microscopes make contact with the patient in order to view the corneal endothelium while many others are strictly non-contact. Determining which is best for your practice is a personal decision and patient comfort should be considered.
Specular microscopy is a noninvasive photographic technique that allows you to visualize and analyze the corneal endothelium. Using computer-assisted morphometry, modern specular microscopes analyze the size, shape and population of the endothelial cells. The instrument projects light onto the cornea and captures the image that is reflected from the optical interface between the corneal endothelium and the aqueous humor. The reflected image is analyzed by the instrument and displayed as a specular photomicrograph In clinical practice, specular microscopy is the most accurate way to examine the corneal endothelium.