EMin5: Slit Lamp Anatomy

Author: Anna Pickens, MD (@AnnaEMin5, Creator of EMin5) // Reviewed by: Alex Koyfman, MD (@EMHighAK); Brit Long, MD (@long_brit); and Manpreet Singh, MD (@MprizzleER)

Welcome to this week’s edition of EMin5 by Dr. Anna Pickens.  Today we’ll review the “anatomy” of a slit lamp! 

These aren’t the easiest machines to work, and each one is a little different.  But if you take a moment to find each of these controls before you walk into your next eye exam, you’ll get a great exam!

Let’s start off with the cheat sheet of controls.  Now since all slit lamps are a little different, you may have to play with yours a little to find the equivalent control, but here are the basics you should look for:

Ok now let’s go through each of these, starting from the beginning. 

1. Power button.   Yes, you must turn the machine on.  But on our machine this is perhaps the greatest achievement, as there are about 5 “on” switches and multiple places the power cords like to fall out.  

Tip – make sure you have the light on and partially focused BEFORE you take it into the patient’s room.  

Also adjust for your eyes:

If you wear glasses, you can chose your prescription (and then take your glasses off while looking through). 

If you don’t wear glasses (or don’t want to take yours off), just keep it at Zero (0). 

2. Patient position:  Ok time to get the table in position.  Adjust the height so that it is comfortable for you both.

And then move the side screws up/down so that that the black marks on the side are even with the lateral canthus of the patient’s eyes.

They should lean forward so that their forehead is touching the white band.  (Or you won’t be able to focus).

3. Aim the light:  Use the joy stick to get the light on the patient’s eyes.

Screwing it clockwise/counterclockwise will usually raise it up and down.

Moving it right/left to scan across the patient’s eye.

Moving it forward and back moves the focus point forward and back (and therefore will help you bring what you see into focus)

4.  Adjust the light:

Find the dial that adjusts the beam from narrow to wide.

(You will use the narrow for the “slit” portion of your exam.  And the wide is helpful when doing a broad sweep of the eye looking for foreign bodies, corneal abrasions, etc).

Then find the one that adjusts the height of the beam.


The knob that adjusts the height of the beam is also where you will find the BLUE LIGHT that you need for the fluorescein exam.   It is at the maximum height setting (usually).

You can also rotate the entire top portion of the machine to pivot the slit vertically vs horizontally.

(Not much use for horizontal for us in the ER, but just be aware that this exists…because I’ve been tricked more than once into thinking all my controls were backwards and later found that the last person that used the machine left it in horizontal mode.)


You will also find a green light (usually on the dial that has different filters).  This is NOT the blue light that we use for fluorescein exam.  (It is for seeing vessels/red blood cells.  Leave that one to ophtho).

5. Lastly you can adjust the magnification.  Start lowest and go up from there, as needed.

Ok now you’re ready to wheel that machine on into the patient’s room and start your exam!

Make sure to include and document:


When you apply fluorescein, apply it to the inner/bottom lid.  Otherwise you could cause an iatrogenic minor abrasion to the cornea, which will show up as a false positive on your exam.


Here’s how to evert the lid to look for embedded foreign bodies:

Infographic courtesy of Mark Ramzy, DO @MRamzyDO 

If you want a more detailed explanation and video, this is an amazing video put together by Dr. Kapasia and Dr. Ali-Ridha that many of the pictures above were taken from.  Check it out!

Kapasi, M., Ali-Ridha, A. Ophthalmic Skills Video – Basics in Slit Lamp Examination. (2014). 



Root, T. Slit Lamp Exam. (2011).  Opthobook.com. 

ALiEM Educational Videos.  Part 3: Using a Slit Lamp.  (2011).


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