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Introduction:
The slit lamp, also known as the bimicroscope, is used on every patient in an ophthalmic exam. It basically consists of a microscope with a light to view the surface of the eye in detail allowing the examiner to detect normal and abnormal eye anatomy. The slit lamp offers the ability for the examiner to look at all the parts of the front surface of the eye in detail. There are different light options- the size of the light beam may be changed for different types of viewing. The light color can be changed to 3 different colors for different types of examination. We will look at the parts of the slit lamp and how they function. We will also discuss how to perform a slit lamp exam and how to document that exam. Doing a thorough slit lamp exam and documenting it properly can save your ophthalmologist time in the examining room with the patient. You will be slow at first when doing a slit lamp exam as you look over each part of the eye separately, however as you become more familiar and proficient with the slit lamp and how to document and what you are looking at, you will be able to do a slit lamp exam in a matter of a minute or 2. In order to use the slit lamp you will need to understand what each of the knobs and levers do. One of the best ways to learn this is to sit down at the slit lamp and work with it to see how to make changes in the light level, size, shape, color, etc.
For an overview of the parts of the slit lamp see the diagram below:
Study the diagram and the parts of the slit lamp, as we will refer to them through out this course. Below you will find an explanation of what each of the parts on the diagram is used for.
Light Brightness/Color indicator: This tells you what type of light you are using on the slit lamp. There are several dots representing different light intensities, and a blue dot that indicates the cobalt blue light. Some slit lamps also have a green light on them.
Tonometer: Used to measure the intraocular pressure. The tonometer rotates in front of the oculars for measuring pressure. It is used in conjunction with the cobalt blue light. The tonometer may be taken off the slit lamp by lifting up on the bar connecting it to the top of the oculars.
Oculars: The examiner views the patient’s eye surface through the oculars. They can be adjusted to accommodate a refractive error for the examiner (so you don’t have to wear glasses), and to accommodate examiner pupil width differences.
Low/High Magnification adjuster: A flip of this lever changes the examiner’s view from low magnification to high magnification.
Chin rest height adjustor: By twisting this the examiner may raise or lower the chin rest to properly position the patient’s eye level so it falls close to the headrest height mark. Proper positioning of the patient ensures that the patient’s eyes fall within vertical range of the slit lamp.
Ocular arm locking screw: Tightening this screw locks the oculars arm in place so it will remain steady. If the screw is not tight the whole arm that holds the oculars may swing easily back and forth. Generally this will be left loose so the arm may swing.
Joystick: This controls the slit lamp height (twist the joystick to raise or lower the oculars), the focus of the slit lamp (push the joystick in or pull it out to focus the light beam on a certain part of the anatomy), the placement of the tonometer when checking intraocular pressure with the optional Goldman tonometer (pushing in gently on the joystick will move the tonometer closer to the patient’s eye.)
Lamp housing cover: This covers the lamp that provides the illumination for the slit lamp. You must remove this cover to change the bulb when it is burned out (remember to unplug the slit lamp before changing the bulb!)
Slit scale: Useful when measuring pathology on the eye-make the slit of illumination the same height size as the pathology you are measuring, and you can read the size off the slit scale.
Filter lever: This slides back and forth to change the illumination brightness (brightest all the way to the left) and is used to change the color of the illumination to cobalt blue for viewing fluorescent dye. If the slit lamp you are using has a green light you will also use this lever to choose that color. The light brightness/color indicator just below this lever indicates the different illuminations or colors.
Slit size adjustment: Rotating this knob changes the height of the slit, you can also change the angle of the slit from vertical (90 degrees) to horizontal (180 degrees) and virtually any angle in between, which is useful when trying to measure pathology (with the slit scale.)
Forehead band: The patient should be instructed to rest his/her head against the forehead band, which ensures that you will be able to get the slit lamp close enough to focus on the patient’s eye. This is also very important when measuring intraocular pressure with the tonometer.
Headrest height mark: This mark gives an approximate height of where you want to have the patient’s eyes so that the slit lamp can be maneuvered to provide adequate viewing of the area around each eye.
Mirror: The light is reflected off the mirror onto the patient’s eye. This is a front surface mirror and thus must be handled and cleaned very carefully to protect the silver coating. It is easily scratched which could interfere with optimum viewing. Dust it carefully with the camel hairbrush that is usually included with a slit lamp.
Chin rest: The patient will rest his/her chin firmly down into the chin rest. This is important because it helps to ensure that the patient will not be moving his/her head up or down (especially important when checking pressure.)
Slit Light width control: Rotating this knob will change the width of the slit of illumination. Using this control and the slit size adjustment knob it is possible to have a small spot of light, a thin slit of light, a large circle of light the size of the cornea, and any size in between.
Locking Screw: The base of the slit lamp is on a bar that allows it to move side to side, and using the joystick it moves forward and backward: tightening this screw will lock the base of the slit lamp so it will not move forward, backward, or side-to-side.
Operating the Slit Lamp
We suggest that you practice using the knobs and maneuvering the joystick, chin rest, and slit lamp table using a fellow employee before working on a patient. This will help you to be more comfortable with what you are doing when examining patients. Follow these simple steps to operate the slit lamp:
- Instruct the patient that you are going to examine the surface of his/her eyes using a microscope with a bright light.
- Have the patient rest his/her chin down snuggly into the chin rest.
- Adjust the height of the slit lamp table using the lever under the table so that the patient is comfortable and is able to touch the headrest firmly with his/her forehead.
- Adjust the height of the chin rest to position the patient’s eyes evenly with the height mark.
- Set the oculars with the correct refractive error and interpupillary distance for yourself so that you can see clearly and binocularly (with both eyes) when looking through them.
- Turn the slit lamp on with the switch on the lower left side of the table
- Turn the joystick clockwise or counterclockwise to put the beam of light even with the patient’s eye level.
- Move the slit lamp closer to the patient (large movements should be made by pushing the base toward the patient, smaller movements by pushing the joystick towards the patient). Stop pushing when the patient’s eye is in focus.
- Adjust the slit size by moving the slit light width control knob.
- To view a particular part of the anatomy position the slit of light on this object, flip the low/high magnification lever to the right to view on high magnification. (See the different types of illumination described below).
What to Look For
Lids, Lashes, Lacrimal system: (L/L)
Inspect the lid margins and lashes for any crusting or dried skin (Scurf)
Check the lid position, does it fall below the visual axis (Ptosis)
Check for any missing or irregular lashes, or lashes turning inward (Trichiasis). Here is an image of an eye with a trichiatic lash:
Check to make sure the lid margins are not turned outward (ectropion), or inward (entropion), which can cause the lashes to rub on the eyes. Here is an image of entropion:
Evert the lids to check for redness, irritation, or bumps (possible papillae)
Evaluate the punctum on the nasal portion of the lid margins to see if they are open (patent)
Check for any bumps on the upper and lower lids- these could be nevi or infections of the lid. An infection of the meibomian gland in the lid causes a bump which is often red- this is called a chalazion. Here is a picture of a chalazion:
Conjunctiva/Sclera: (C/S)
Look at the conjunctiva (the mucousy clear covering over the white sclera)-
Are there any blood vessels that make the white part of the eye look red (injection)
Are there any yellowish bumps on the conjunctiva/sclera at 3:00 or 9:00 (Pinguecula)
Are there any wedge shaped defects that look like conjunctiva growing onto the cornea (Ptyergium)
If you work in ophthalmology for any length of time you will surely encounter the patient who calls complaining of a very red eye- like blood in one part of their eye- This often is due to a subconjunctival hemorrhage- which is simply put a broken blood vessel that bleeds under the conjunctiva. There is really not much that is done for this (unless the patient experiences these often). They look much worse than they are and usually take a few days for the blood to reabsorb. Here is a picture of a subconjunctival hemorrhage:
Subconjunctival Hemorrhage
Photo credit Eye Institute Columbia Univ.
Cornea: (K)
The cornea should be transparent without scarring or haze.
Look for haze around the limbus (the outer edge of the cornea) - (Arcus)
Blood vessels growing into the cornea (Pannus or neovascularization)
Look at the innermost layer of the cornea for:
Pitting on the surface somewhat like a golf ball (Guttata)
Pigment deposition on this layer (This can be a sign of possible pigmentary dispersion syndrome which could cause glaucoma)
Look at the layers of the cornea for opacities. Small whitish areas may be corneal
infiltrates:
Instill a drop of fluorescein dye looking at the surface of the cornea for punctate dots of stain (SPK or superficial punctate keratitis). Here is a picture of a cornea with linear (a line pattern) of keratopathy:
A tree branch like pattern on the corneal surface could be caused by Herpes Simplex Virus (HSV). This is called a dendrite. Here is an image of dendritic HSV:
Iris: (I)
Look at the iris to make sure that the pupil is round and that there are no irregularities in the shape of the iris or pupil: (a keyhole shaped pupil is known as Iris Coloboma, many times after trauma directly to the eye the pupil will be irregularly shaped, some patients have an irregularly shaped pupil after cataract surgery)
Look for any holes in the iris
A small hole is called a Peripheral iridotomy-made with a laser
A larger hole is called a Peripheral iridectomy, here is an image of a patient with a peripheral iridectomy:
Check to see if these holes are still open (patent)
Look for irregular blood vessels in the iris (these will usually be seen on the surface and will be very squiggly-called Rubeosis)
Look for areas where the iris and innermost corneal layer are stuck together (Anterior synechia)
Look for areas where the iris and lens are stuck together (Posterior synechia)
Anterior Chamber: (AC)
Evaluate the depth of the anterior chamber and notate if it is deep or shallow
Look for evidence of inflammation (cell and flare)- cells will look like small specs of dust which usually float around, and flare is the ability to see the light from the slit lamp in the anterior chamber (cell is like seeing the dust in the air when looking into the beam of light from a movie projector, and flare is like seeing the beam from the movie projector going through the air.)
Check for any blood that could have collected at the bottom of the anterior chamber (hyphema)-this may be seen in cases of direct trauma to the eye. Here is an image of a Hyphema: