Anterior Segment Imaging
The eye is broadly divided into the anterior (front) and posterior (back) segments. The anterior segment of the eye includes the following:
- Iris: the round pigmented part of the eye, which has a black opening at the centre called the pupil
- Sclera: white of the eye
- Cornea: transparent membrane in the front of the iris
- Conjunctiva: mucous membrane that lines the cornea and sclera
- Lens: transparent structure located behind the iris and pupil which focuses light
- Ciliary body: encircles the lens and controls its shape. It also secretes a fluid (aqueous humour) between the cornea and the lens.
The structures of the anterior segment are important for vision and may be affected by various conditions such as conjunctivitis, corneal abnormalities, cataract, refractive errors and trauma. Non-invasive high-resolution imaging is often essential for the diagnosis and treatment of many of these conditions.
Some of the instruments used include:
- Slit lamp: This conventional imaging technique focuses a narrow, intense beam of light on your eye. It helps your doctor identify abnormalities of the anterior structures while looking through a microscope.
- Ultrasound biomicroscopy: This instrument uses high-frequency sound waves to create detailed images of the anterior segment including structures such as the ciliary body, which are difficult to visualise by conventional methods.
- Specular microscopy: A photographic technique that determines corneal thickness and evaluates the cells of the cornea. It projects light onto the cornea, analyses the reflected image and expresses its results as a highly magnified digital image.
- Anterior segment optical coherence tomography (AS-OCT): Uses near-infrared light to create detailed cross-sectional images.
- Scheimpflug system: Images the eye at an angle to the slit-lamp beam to create sectional images of the cornea and lens.