Image courtesy of: https://eyeguru.org/essentials/slit-lamp-tips/

How to use the slit lamp: 7 key skills to learn

The slit lamp is the core instrument of optometry and ophthalmology, and you want to be able to quickly master its use in the first month of your residency. We’ve collected the most high yield tips to get you examining like a pro. These are the hard things that all beginners struggle with.

#1: Positioning Yourself

Get yourself positioned before the patient. you can always raise or lower the pt’s chair to get them in position, but if the slit lamp isn’t at the right height for you, it’s much more difficult to adjust your own chair .

Many trainees and residents, most of the time ignore personal ergonomics. You will regret it later when poor habits lead to neck strain, poor exams, and fatigue.

Later on, many folks who, by the time of fellowship, have neuropathies and back pain.

Get your chair at the correct height to sit comfortably and adjust the table so you can sit up straight while looking through the oculars.

Never duck your head, never tilt your head, never use the slit lamp while standing.

The patient

The following steps should take you less than 15 seconds when you get fast. These will set you up for success even if you need to do a 15 minute exam. It’s crucial that the patient is comfortable. They are much more likely to be able to keep their eyes open, look in the directions you want them to look, and stay still.

Clean: Clean the applanation tonometer, chinrest, top strap, and handles. Patients will be much more cooperative with your exam when they don’t see another person’s makeup or dandruff clinging to the plastic.

Position the patient’s head: Get your patient positioned correctly: chin in the cup, forehead against the top strap. Line the patient’s eyes up with the markings on the side of the patient stabilization frame. This is crucial. Otherwise, you’ll be moving patients around after both of you are already settled.

Instruct the patient: We should, kindly always tell the patient: “Grab these handles like you are riding a motorcycle.” This keeps the slit lamp table super stable and safe for when you are applanating, removing sutures, etc.

Adjust the patient’s chair: Move the patient’s chair up or down to get the patient’s height correct.

#2: The dilated retinal exam

*Note: This exam should only be performed on patients who have anterior chamber "Open Angle" as illustrated bellow.

Image courtesy of: https://www.opticianonline.net/cet-archive/4744

During your first few days, you’ll feel like you’ll never see the retina. After a week of practice, you’ll wonder why you ever struggled.

This is really a matter of practicing to build muscle memory. Each lens has an optimal distance from the eye and slit lamp. Younger individuals with relatively healthy eyes are the best to start practicing on.

Older individuals with pathology like cataracts or old vitreous heme will make it difficult to see the fundus initially and it may be hard to tell if your technique is wrong or of it’s just a difficult view. The general approach is this:

Set up your beam. Photophobia is your worst enemy. It’s better to use a dimmer illumination rather than having your patient struggle against you.

Wider and shorter is recommended when you’re learning the ropes. A shorter beam (5 to 6 mm tall) helps to decrease photophobia and a wider beam (~1.5 to 2 mm wide) helps to integrate what you’re seeing.

Hold the lens about 5-7mm (varies based on lens) from the patient’s eye with your index finger and thumb. Brace your other 3 fingers against the top strap or the patient’s face. Now, swing it out of the way while you position the beam.

Align the slit lamp beam so it is perpendicular to the patient’s eye, going straight through the pupil. Looking through the slit lamp, you should be able to see the red reflex, the beam should be traveling perfectly through the center of the pupil, and the iris should be in focus.

Note: The red reflex can also be observed using a simple retinoscope.

Now, swing the lens into the path of the light and start backing away in a straight line.

Pro learning tip: Before you start backing away with the joystick, you can move your head to the side and check to see if your lens is aligned properly. You should be able to see the slit lamp beam going through the lens and hitting the patient’s pupil.

As you start backing away with the slit lamp, you’ll see a hazy red glow which should sharpen when you are focused. You can also play with the angle of your lens and the distance from the eye to try to get the image more crisp.

Once you see the retina, adjust the slit lamp rather than the lens to explore your view. You can adjust up, down, left and right.

It is estimated that about 80% of your patients will be older and have ptosis, be photophobic to any light, or will simply be unable to keep their eyes open.

In these patients, you will have to open the lid. You can do this with your 3rd and 4th fingers while you hold the lens with your thumb and index finger. It’s tricky, but it’ll become second nature with practice.

Note: It is also possible to ask a colleague to use a Q-Tip to hold the patient's eyelids open while your concentrate on the slit lamp maneuver.

Illustration of patient with "Narrow or Close Angle". Dilation of pupil must be avoided on patients with this condition:

All anterior chamber open and narrow angle images are a courtesy of: https://www.opticianonline.net/cet-archive/4744

Images are a courtesy of: https://www.opticianonline.net/cet-archive/4744

#3: The undilated optic nerve exam

When the dilated slit lamp exam is second nature to you, the undilated exam will be the next step. This exam is crucial for glaucoma patients, as we normally don’t dilate those patients in clinic as it can raise the IOP unnecessarily. Here is the general approach:

Use a smaller beam to reduce glare reflected from the iris. Try a 1.3 mm wide by a 3mm tall beam.

Positioning is key. Have your patient look 15-20° temporally on the eye you are examining. It puts the optic nerve in view when you look in. This is where you hear the phrase “please look at my right ear” for examining left eyes, and vice versa. Another good reference target is the goldmann applanation tip, or the equivalent horizontal part of a teaching side scope.

Follow the same steps as the dilated retinal exam, but realize your view will be the size of the optic nerve head at best, and you will often not have a binocular view.

#4: Moving around in the eye

One of the most frustrating things that beginners experience is being unable to shift your field of view significantly once they get a good view of the fundus. Try the following:

“Walk the dog”: The best way to move your field of view is not to move the joystick OR the lens independently. Rather, move BOTH the joystick on the slit lamp AND the lens in the same direction VERY slowly simultaneously.

This is a game changer for many people we teach. Once you master this, you will be shocked at how much you can see when the eye is in primary position. In undilated exams, the only way to move around and consistently find the fundus and the macula is by using this technique.

#5: Checking for cell and flare

The right magnification is key! Use only the 16x mag with the beam of light angling in from the side. Always use the brightest light in the darkest room! Look for cells over the pupil, it’s the darkest part giving you the greatest contrast. Use the following SUN grading criteria to grade your exam.
SUN Grading Scheme for Anterior Chamber Cells:

Grade               Cells in Field
0                      < 1
0.5+                 1 – 5
1+                    6 – 15
2+                    16 – 25
3+                    26 – 50
4+                    50+
(using 1mm slit beam)
SUN Grading Scheme for Anterior Chamber Flare:
Grade              Description
0                     None
1+                   Faint
2+                   Moderate (iris/lens details clear)
3+                   Marked (iris/lens details hazy)
4+                   Intense (fibrin/plastic aqueous)

#6: Checking intraocular pressure by applanation

By the end of your first year of residency, you’ll have performed this step at least a few thousand times. Here is how to do it your first time:

Put a drop of fluorescein dye into your patient’s eyes.

Clean the applanation tip or use a new tip: follow your institution’s guidelines.

Swing the beam of light to about 45 degrees off midline and swing the applanator inline until you feel it click

Adjust the prism (the applanation tip) so it is also facing midline.

Flip your lamp to the blue setting, turn the brightness ALL the way up. This may require increasing both the beam width and the slit lamp power setting.

Now, look into the oculars to ensure you see that the prism is horizontal.

Tilt the control stick all the way back. This gives you fine control to push forward and land gently on the cornea! If you don’t do this, you’ll end up jerking the lamp around when you are very close to the cornea. Not only will your patient get scared, but they will start reflexively closing their eyes when you get close!

Now, with the control stick tilted back, move forward to within 3-5 mm of the cornea.

Push the control stick forward, using its fine control to move forward and land gently on the corneal surface.

When you do this successfully, you will see the mires, and you will be able to adjust the dial accordingly.

#7: Gonioscopy

The most advanced skill. Gonioscopy.org has a great set of videos on this, and they explain it well here: http://www.gonioscopy.org/

References:

https://eyeguru.org/essentials/slit-lamp-tips/

https://www.opticianonline.net/cet-archive/4744

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