As with any specialized area of study, ophthalmology has its own complex array of terminology, machinery, and processes. This section of the encyclopedia gives insight into some of the "tools of the trade", describing most of the unique technologies you might encounter if you spent a lot of time at your ophthalmologist's office.
LensThe lens is a dense, transparent structure made of proteins, located just behind the iris and pupil. Its curvature and density cause light waves to bend as they travel through the lens. After passing through the lens, the light waves converge and project an inverted image on the retina. The retina changes the light waves to electric impulses that then travel along the optic nerve to the brain. This entire series of events results in a visual and understandable representation of light and color.
The lens also changes shape in order to focus on objects at various distances. The older one becomes, the stiffer and more inflexible the lens becomes. Oftentimes, the lens becomes so stiff that it cannot change its shape sufficiently to accommodate both images of objects up close and far away. This is why the need for bifocals or reading glasses are common as people age.
New, thin layers continually grow over old layers of the lens. These layers of cells grow inward from the edges but never form in the center of the lens. If the cells at the center of the lens grow cloudy, cataracts develop. Natural lenses can be replaced with artificial lenses in a relatively fast and easy surgical procedure, making cataracts an easily treatable disease.
AnatomyDiagrams and descriptions of the parts of the eye.
Our eyes allow us to perceive light, dark, and color in astonishing detail, revealing the beauty and complexity of the world around us. Perhaps even more extraordinary is the fact that this organ of vision measures just 24mm (0.95 inches) and weighs 7.5 grams (0.25 ounces)!
The eye's many complex structures, some more obvious than others, are mostly unknown outside of the medical field. In an attempt to eliminate any mysteries, our encyclopedia offers easy to understand definitions of most of the terms you're likely to hear in your ophthalmologist's office, and cross-references them with other relevant terms when appropriate.
DiseaseUnfortunately, as with the rest of our body, there are many diseases that can effect our eyes. Most are obscure and exotic, and few of us will ever experience them outside of medical textbooks.
There are, however, a small handful of diseases that are part of the common experience. We list most of them here along with consice definitions and relevant information so that you can be better informed. Whether it's you or it's a loved one is experiencing eye problems, you owe it to yourself to be better informed.
TreatmentThis section of the encyclopedia is intended to let you know what treatments may be available for various ophthalmic disorders, and to shed light on what each involves. If your ophthalmologist is recommending a particular treatment, you should consider this a starting point for a deeper conversation about what your particular case may involve, as everyone has slightly different specific requirements.
Optical Coherence Tomography (OCT)Optical Coherence Tomography (OCT) is, perhaps, the most promising technology available to produce images of the eye. During the simple procedure, a laser quickly scans the dilated eye. Unlike other imaging methods, such as ICG and FA, which produce top views of the retina, the image produced is a cross-section of the layers of the retina. Each of the thin layers of photoreceptors, nerve cells, and pigment epithelial cells are clearly delineated.
A high-quality image will show where abnormalities have occurred, such as the formation of drusen or new blood vessels, or the detachment or breakage of any of the retinal layers. OCT is an important tool for the diagnosis and treatment of many retinal conditions.
Below is an OCT showing a cross-section of the retina, revealing pockets of fluid (the dark areas "sandwiched" between the green layers of retina) under the surface.
Indocyanine Green (ICG) AngiographyIndocyanine Green (ICG) Imaging is similar to fluorescein angiography (FA). Like FA, it is a useful tool for the diagnosis and treatment of several forms of macular degeneration and retinopathy. It is more effective than FA in producing images of blood vessel growth and damage in the deeper choroid layer behind the retina. It is also able to produce a better image than FA if blood is present in the macula.
The process is generally safe, with a minimum of discomfort, and is usually done in the doctor’s office. It involves dilating the eyes being photographed, and an injection of the green dye, usually in the arm, which circulates throughout the body, including the choroidal layer of the eye. A flash illuminates the eye and the resulting images are stored on a digital camera system. The fluorescent light that the indocyanine green dye emits can help to identify abnormalities in the circulation of the choroid. A series of images, or a movie of the dye moving through the vessels of the choroid, will help the ophthalmologist to decide upon the best treatment to prevent further vision loss.
Most ophthalmologists consider ICG angiography to be an adjunctive or secondary test which adds further information to the clinical picture, and is often done in addition to a fluorescein angiogram.
Below is an example of a typical Indocyanine Green angiogram, revealing an area of leakage (the bright area) just outside the macula in the center of the image. The optic nerve can be seen to the left.
Fluorescein Angiography (FA)Fluorescein angiography (FA) is a technology that allows photographs of the blood vessels of the retina to be taken. It is a useful tool for the diagnosis and treatment of several forms of macular degeneration and retinopathy as well as other disorders.
The process involves injecting the dye into a vein in the arm, just after the eyes have been dilated with eye drops. The yellow dye will travel throughout the bloodstream, including the vessels of the retina. It will fluoresce, or emit light, when an extremely bright light is flashed into the eyes. A series of photographs will show the entrance and exit of the dye through the blood vessels of the retina and just beneath it. Any areas of abnormal new blood vessel growth, leakage, or blockage, will appear darker or brighter than normal angiograms of the vascular retinal area.
The process is generally safe, with a minimum of discomfort, and is usually done in the doctor’s office. It is an important tool, because it will reveal the location of damage by leaking or pooled blood and will show where new blood vessel growth is occurring. This will help the ophthalmologist to decide upon the best treatment to prevent further vision loss.
Below is a typical flourescein angiogram showing an eye with leaking vessels (the bright area) in the middle of the macula. The optic nerve is seen to the right.
Amsler GridThe Amsler grid is a simple square chart with a dot in the middle of what resembles graph paper, and can be used to test ones central visual field while at home. The lines are usually black, and the background white, though sometimes the colors are reversed. The test is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration, Epiretinal membrane), as well as the optic nerve and the visual pathway to the brain.
When taking the test, the patient will be asked to look at the grid and concentrate on the dot in the middle, using one eye at a time. If the lines near the dot appear wavy, blurred, or are missing, macular degeneration, and the loss of central vision, may be occurring. The distorted image of the grid is not an optical illusion but is evidence that some photosensitive cells in the macula may have been destroyed, obscured (usually by blood) or displaced (as in a retinal detachment).
CataractCataracts are the opaque, or milky, areas that can form in part or all of the crystaline lens of the eye. They often start with only a slight disturbance of normal vision, often going unnoticed for years, and can slowly increase in opacity until they completely interfere with vision. Some of the early effects of a cataract are a decrease in contrast sensitivity and color intensity, but eventually they also decrease visual acuity.
There are many possible reasons for developing a catartact, including age, excess exposure to ultraviolet light and radiation, physical trauma to the eye, secondary effects of diseases such as diabetes or hypertension, and the side effects of certain drugs such as corticosteroids. There may also be a genetic component to certain forms of cataracts. Cataracts are classified by a number of terms that include: partial, complete, hard, soft, stationary or progressive, nuclear, cortical, mature, and hypermature. They may also be classified as being posterior or anterior, referring to thier location.
Surgery ro remove "mature" cataracts is common and is often performed with only a local anaesthetic on an outpatient basis, allowing the patient to go home the same day. The surgery removes the old lens and replaces it with a plastic one, referred to as an intraocular lens, or IOL. Endophthalmitis and retinal detachment are some of the possible complications of cataract surgery.