Lesson 18 - Slit Lamp Biomicroscopy

Question 1

Direct illumination (also called optic section)

Answer 1

This is the most common type of illumination used for seeing depth of structures, determining corneal thinning as well as cells within the eye. Position the microscope directly in front of the patient and position the lamp 45 degrees between the ear and the eye. Keep the slit width narrow, in a vertical position and with the illumination low. Focus the beam on the cornea until you see two beams, one on the corneal surface and the other on the iris surface. Using the joystick, scan across the cornea.

Question 2

Indirect illumination

Answer 2

Used to assess the anterior chamber. The beam should be 2-4 mm wide, focus on the cornea, then focus on the lens, and then focus in between these two structures. You’ll be focused on the anterior chamber.

Question 3

Diffuse illumination

Answer 3

For a good overall view of the cornea, lids, lashes, iris, and conjunctiva. Set the beam at 45 degrees and use a wide beam. Set the magnification and the illumination low, and then open the slit beam and fully illuminate and focus on the cornea.

Question 4

Specular illumination

Answer 4

Used to view the tear layer, cells in the endothelium, and posterior and anterior.

Question 5

Sclerotic illumination (also known as sclerotic scatter)

Answer 5

Used to assess contact lens fitting and corneal clouding. Use a wide beam aimed at the limbus of the cornea, using a low angle, and the microscope should be focused on the cornea. The entire cornea should be seen at once. Use low magnification and align the lamp and microscope at 45 degrees, putting the microscope in front of the eye. Focus on the temporal part of the corneal limbus, and you should see a halo surrounding the cornea.

Question 6

Transillumination (also known as retroillumination)

Answer 6

Used to see blood vessels in the cornea, corneal depth, epithelial scars, and edema as well as opaque features in the crystalline lens. Uses light reflected from the back of the eye. The angle between the microscope and lamp (medium illumination) should be 60 degrees. Slit should be 2-4 mm obliquely focusing on the cornea. The features you will see will be opaque against a light background or scattered to light.

Question 7

Splitting K

Answer 7

Using the average of the two keratometry readings

Question 8

Slit lamp power switch

Answer 8

Power switch turns the machine on and off.

Question 9

Forehead rest and height marker

Answer 9

Used for lining up the eye at the correct height

Question 10

Joystick or “aim light” in this illustration

Answer 10

Used to move the lamp and oculars inward, outward, and also up and down.

Question 11

Adjust beam

Answer 11

Used to adjust the width and/or height of the beam

Question 12

Cobalt filter knob

Answer 12

This knob flips on the cobalt filter in front of the lamp so when fluorescein dye is used on the cornea, it absorbs the blue light and highlights damaged corneal tissue. Just above this is a knob to flip the cobalt filter in front of the beam. This knob also enables you to flip in a filter to dim the intensity of the lamp and adjust the size of the circular light.

Question 13

Intensity knob

Answer 13

Near the power switch there is usually a slit lamp intensity knob that adjusts the brightness of the lamp.

Question 14

If you are going to be fitting contact lenses, it is important to determine if the patient’s cornea is healthy before fitting them with a contact lens, so we need to discuss how to evaluate the corneal status. If the health of the cornea is compromised in any way, or if the cornea has any damaged area where the cells have been affected, a foreign body, dryness, or a scratch, fluorescein-dyed areas can be seen and highlighted by the what on the slit lamp? These areas will appear to be what color?

Answer 14

If you are going to be fitting contact lenses, it is important to determine if the patient’s cornea is healthy before fitting them with a contact lens, so we need to discuss how to evaluate the corneal status. If the health of the cornea is compromised in any way, or if the cornea has any damaged area where the cells have been affected, a foreign body, dryness, or a scratch, fluorescein-dyed areas can be seen and highlighted by the cobalt blue filter on the slit lamp. These areas will appear to be bright yellow or a bright lime green.

Question 15

A fluorescein strip

Answer 15

A fluorescein strip is a strip of litmus paper embedded with some dried fluorescein dye. The fluorescein strip is slightly damped with sterile saline and then lightly touched to the eye just below the cornea.

Question 16

After the eye has been stained, you’ll use the slit lamp to look for irregularities in the stain pattern. For example, a contact lens cannot be fitted to a client that what?

Answer 16

After the eye has been stained, you’ll use the slit lamp to look for irregularities in the stain pattern. For example, a contact lens cannot be fitted to a client that has a scratch on their cornea, epithelial erosions, corneal ulcer, or a corneal abrasion.

Question 17

Scratch on the Cornea

Answer 17

This cornea cannot be fitted with a contact lens of any kind until the cornea has completely healed. If you see this prior to fitting any contact lenses, your patient should see their eye doctor first.

Question 18

Epithelial Erosions

Answer 18

In this stain pattern, you can see that the fluorescein dye appears grainy. This shows epithelial erosions, a breakdown of the outer layer, and must be addressed by the doctor before fitting for contacts.

Question 19

Dry Eye

Answer 19

If you see these types of staining on the eye during your prefitting evaluation, you should refer your patient to their eye doctor for treatment. Wearing a contact lens on this eye will further irritate the eye and risk infection.

Question 20

Corneal Ulcer

Answer 20

This stain pattern shows a highlighted green dot on the cornea, which is indicative of a corneal ulcer. Corneal ulcers are caused by bacteria. You should definitely not fit a contact lens on this eye, and make sure the patient is treated by their doctor first. An ulcer can sometimes lead to a permanent scar and, if it is in the center of the eye, will affect vision permanently.

Question 21

Cornea Abrasion

Answer 21

Caused by a foreign body that struck the eye. If you see anything disruptive to the cornea, do not apply any type of contact lens on this eye and immediately refer the patient to their eye doctor for treatment. Similar to the cornea ulcer, if this is in the center of the eye over the pupil, it may cause a permanent scar and affect the vision permanently.

When you stain the eye with fluorescein and you see anything that stains, you should refer your patient to their eye doctor first before fitting any type of contact lens on the eye.

Question 22

Parallelpiped illumination

Answer 22

Used for looking at the endothelium, at specific tissue layers in the cornea, and to see irregular surfaces on the cornea. Beam is full height and 5-7 mm wide.

Question 23

In addition to illuminations, you will also use basic fluorescein and the slit lamp to assess what?

Answer 23

In addition to illuminations, you will also use basic fluorescein and the slit lamp to assess the fit of rigid gas-permeable contact lenses.

Question 24

Describe the factors which make a good rigid gas-permeable (RGP) contact lens fit?

Answer 24

There are three zones: optic, intermediate, and peripheral. You can see some fluorescein under the central optic zone area, evenly spread. The optic zone should completely cover the pupil area wherever the pupil moves while wearing the contact lens. It is where the prescription power of the lens is. The slight bearing of the lens in the intermediate zone, showing almost no dye, which is the ring just outside the optic zone. The peripheral zone should show more pooling of dye, since you want a good edge lift for good tear exchange under the lens.

Question 25

RGB contact lens fit: too steep

Answer 25

There is much too much dye in the optic zone as the lens vaults over the cornea. The secondary peripheral zone has too much bearing over a wider area, and the peripheral curve has too little dye, not enough edge lift with almost a seal-off effect. Here you can most likely notice how the edge of the lens is bearing down and indenting the cornea. Sometimes you will also see the limbal blood vessels engorged.

Question 26

RGB contact lens fit: very steep

Answer 26

Sometimes the lens will be so steep there will be an air bubble under the lens.

Question 27

RGB contact lens fit: too flat

Answer 27

You can see the bearing of the contact lens on the optic zone leaving no dye under it. The secondary peripheral zone is where all the dye is pooling as the lens is lifted up more toward the periphery.

Question 28

Remember that a corneal astigmatism is when the front surface of the cornea is not spherical, and it is somewhat like the surface of a grape or an egg. When fitting a spherical gas-permeable lens on this type of cornea, you will see what?

Answer 28

When fitting a spherical gas-permeable lens on this type of cornea, you will see more pooling of dye where the cornea is steeper and black where there is not dye and the cornea is flat.

Question 29

RGP contact lens fit on astigmatism: against-the-rule (cornea flatter vertically)

Answer 29

If you have a cornea that has a lot of against-the-rule astigmatism and put a spherical contact lens on it, you will see a pattern like this. It follows our definition of the cornea being flatter in the vertical direction in against-the-rule astigmatism. You would most likely need a bitoric lens with two curves on the backside to fit this cornea.

Question 30

RGP contact lens fit on astigmatism: with-the-rule (cornea flatter horizontally)

Answer 30

Remember with-the-rule astigmatism is when the cornea is flatter along the horizontal axis. Here you can see that the lens is bearing along the horizontal axis where the curvature of the cornea is flatter.

Question 31

If the corneal astigmatism is not too great (less than 1.50 diopters), you can get an acceptable fit how?

Answer 31

If the corneal astigmatism is not too great (less than 1.50 diopters), you can get an acceptable fit by using the base curve between the flattest and steepest keratometry reading.

For example, if the K readings are 42.002180 and 44.00 at 090, you can start with a base curve of 43.00 diopters. This is known as “splitting K.”