Ophthalmic Imaging Glossary
Anterior Segment - cornea, iris, lens and associated structures of the eye
Cataract - An opacity of the lens of the eye.
Choroid - The layer underneath the retina.
Cornea - The transparent dome on the front of the eyeball.
Dilation - Expansion of the pupil using eye drops to allow observation of the lens and retina.
Fixation - Ability of the eye to maintain a fixed orientation.
Fluorescein Angiography (FFA) - Angiography is the definition of a vessel or structure using a contrast medium. Contrast medium (sodium fluorescein dye) is injected into a vein in the patients arm and timed photographs are taken using a fundus camera or SLO system. Fluorescein angiography is an important ophthalmic diagnostic test used to examine the blood vessels and associated structures of the retina. It is used to diagnose sight threatening ophthalmic conditions and to locate areas that require treatment.
Fundus Camera System - A modern fundus camera system is a semi-mobile floor mounted ophthalmic instrument costing £50,000. This complex system is used to produce high-resolution photographs of the patient’s retina.
Fundus Photography - Photography involves the patient’s pupils being dilated, the patient’s head is immobilized and the camera positioned close to the eye. The photographer observes the retina by adjusting illumination and carefully positioning the eye using external & internal fixation points.
Gonio Photography – Photography that involves the use of a contact lens that is in direct ocular contact.
Heidelberg Retina Angiograph (HRA) – The HRA is a floor mounted imaging system that comprises a laser imaging unit, patient head support and computer workstation with an image database. Diagnostic capabilities include auto fluorescence, stereo and wide field imaging, and high-speed angiography.
Heidelberg Retinal Tomography(HRT) - The HRT is a floor mounted imaging system that comprises a laser imaging unit, patient head support and computer workstation with an image database. It produces three-dimensional images of the optic nerve and structural data that are used to monitor the subtle changes caused by raised internal pressure within the eye of a patient with glaucoma.
Indocyanine Green Angiography(ICG) -Angiography is the definition of a vessel or structure using a contrast medium. Contrast medium (Indocyanine Green) is injected into a vein in the patients arm and timed photographs are taken using a fundus camera or SLO system. ICGAngiography is an important ophthalmic diagnostic test used to examine the blood vessels and associated structures of the choroid. It is used to diagnose sight threatening ophthalmic conditions and to locate areas that require treatment.
Iris - The coloured part of the eye that expands and contacts to regulate the amount of light entering the eye through the pupil.
Lens - The transparent structure behind the iris and pupil of the eye that focuses light onto the retina.
Optical Coherence Tomography (OCT) - OCT is a non-destructive imaging technique that uses the optical backscattering of light to rapidly scan the eye and describe a pixel representation of the anatomic layers within the retina. Each of these ten important layers can be differentiated and their thickness can be measured.
Ophthalmic Angiography - Refers to both Fluorescein and ICG Angiography.
Pupil - The circular opening in the centre of the iris through which light passes into the eye.
Retina - The retina is the internal back surface of the eye containing the light sensitive nerve layer.
Scanning Laser Ophthalmoscope (SLO) – An instrument that uses low powered lasers to image the retina or choroid.
Slit-Lamp Photography - A slit -lamp camera is static floor mounted ophthalmic instrument costing £18,000. It is used to produce high magnification photographs of the patient’s cornea, iris, lens and eyelids. Photography involves delicate adjustment of illumination and careful positioning of the patients eye.
Specular Microscopy - The specular microscope camera is a static floor mounted ophthalmic instrument costing £10,000. It is used to produce very high magnification photographs of the cell layer (endothelium) on internal back surface of the patient’s cornea. The photographer applies anaesthetic drops to the patient’s cornea (training necessary) and places the camera lens cone in direct contact with the eye. The photographer uses the photographs to produce a cell density count, which allows the doctors to assess corneal health and decide if the patient requires a corneal graft.
Department of Medical Photography October 2004