Bio-microscope or "slit lamp" examination


An instrument called a bio-microscope or slit-lamp is used by the eye doctor to evaluate both the external and internal health of your eyes. A bio-microscope is a combination of a stereo-microscope and a highly focused beam of light that can be narrowed into a slit. The narrow slit of light allows the doctor to see fine detail in structures that are essentially transparent, like your cornea and the lens of your eye.  Conditions frequently detected by use of the bio-microscope are disorders of the eyelids and lashes, dry eyes, foreign bodies, "pink eye" (conjunctivitis) and catatracts.


Other slit-lamp tests - Sometimes the doctor may place a hand-held lens in front of
the light beam. This gives the doctor a three-dimensional view of the more-internal eye structures like the retina. The bio-microscope, when fitted with an attachment called a "tonometer" can also be used to measure the pressure inside your eye (glaucoma test.) In this test, a short-acting anesthetic drop and fluorescent dye are placed in your eye. The pressure-sensitive tip of the tonometer is gently placed against your cornea, while a deep-blue light is shined onto the tip of the tonometer. The blue light is used to make the dye fluoresce and indicate to the doctor when the pressure reading is correct.

Some tonometers measure the intraocular pressure by directing a brief puff of air gently onto the eye. "Air puff" tonometers work well and are frequently used as screening instruments because no drops are required. In glaucoma patients or glaucoma suspects, the tonometer/bio-microscope combination is usually used for added precision.


Ophthalmoscopy

Ophthalmoscopy is a test that allows the doctor to see the inside-back of the eye using a instrument called an ophthalmoscope. An ophthalmoscopic examination is unique because it allows the doctor to directly observe the small vessels of the circulatory system. The vessels inside the eye are similar to the small vessels found in the brain and kidney. Changes seen in the eye are a strong indication that the same changes are occurring elsewhere in the body. High blood pressure (hypertension) and diabetes are two diseases which often cause changes in these small vessels. Head injuries or brain tumors may also cause changes inside the eye that can be detected during ophthalmoscopy.
	To see what the doctor sees, click image to enlarge.
Two kinds of ophthalmoscopes may be used by the eye doctor--direct and indirect. Direct ophthalmoscopes are about the size of a small flashlight and have a series of lenses that can magnify up to about 15 times.  Indirect ophthalmoscopes are worn by the doctor like a miner's light. The doctor also holds a small lens about 3 inches from your eye which magnifies about 3 to 5 times. Indirect ophthalmoscopy provides a wider view of the inside of the eye and allows a better view if the lens of the eye is clouded (cataract.) Ophthalmoscopy often requires dilating the pupils with drops to give the doctor an adequate view inside the eye. Perimetry (side-vision) testing A perimeter is used to test your visual field. Your visual field includes both your central and side vision. During this test, while you are seated comfortably, you will be asked to look straight ahead at a central fixation target. You will probably be instructed to press a button when you become aware of a small light anywhere within your peripheral field. It's important that you keep your eyes focused on the central target throughout this examination so that an accurate reading of your visual field is obtained. This test can detect vision loss, even if the loss is far to the side or quite subtle.  Even a large and profound vision loss in one eye's visual field can go unnoticed by a patient because the visual field of the opposite eye overlaps it to a great extent. One eye simply "fills in" the area of vision loss present in the opposite eye.  This is why the side-vision test is always administered to eye separately. The nerve pathways from the retina to the part of the brain where vision is interpreted are very uniform from person to person. Because of this uniformity, visual view analysis has a great deal of diagnostic value. Glaucomatous visual field loss usually follows a particular pattern. Other diagnostic patterns of visual field loss can indicate retinal detachment and neurological diseases, adding significantly to the value of this test. The nerve pathways for vision are long and cross over many brain structures on their route from the eye to the very back of the brain (visual cortex.) Neurologists make great use of visual fields to help them determine where in the brain a tumor or other pathology is located. If you've ever wondered why an eye examination is recommended, when you want a new pair of glasses or contacts and you "see just fine", we hope you now understand why. There really is a lot more to a thorough examination than "meets the eye." Vision & Health Newsletter courtesy of:   Back to Top Dr. Philip Smith & Associates 1855 1st Ave #100 San Diego, CA 92101 619-297-4331