Monday Back to Basics

Slit Lamp Basics

Revamped from our archives, the fabulous Dr. Alexis Pelletier-Bui teaches us how to use a slit lamp! This comprehensive post reviews all the knobs and buttons of the equipment, then shows how to use it to perform the exam.

COMPONENTS OF THE SLIT LAMP

(These photos are based on a Weiss SL 120 Slit Lamp – other models might be slightly different but the ideas are the same!)

Think of this part as a microscope.

#1 – Oculars – Adjust for your personal interpupillary distance

#2 – Magnification Dial – Can set to 5x, 8x, 12x, 20x, or 32x

#3 – Focusing Ring – Accounts for your personal refractive error.  If you have 20/20 vision or correction lenses, it should be set to 0. 

This part is your light source.  It can be swung 180 degrees side to side to allow for examination from the temporal or nasal side.

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#4 – Beam height – Move to the right of examiner > shorter.  

#5 – Beam widgth – Move to the right of the examiner > smaller

#6 – Color of light – 3 options: White (used for most of the exam), Cobalt blue (used with fluorescein exam), Green (aka red free filter; allows blood vessels to appear black; rarely used by ED doc)

#8 – Forehead Strap

#9 – Chin Rest

#10 – Height Adjustor – twist this to raise or lower the chin rest

#11 – Joystick – Allows movement of the viewing & illumination arms in tandem.  Large movements forward & backward are often required to obtain initial focus which will require pressure on the joystick to move the entire base.  Smaller microadjustments can be made with smaller movements of the joystick (without moving the base).  Movement side to side and up & down (the latter performed by twisting the joy stick) allow for you to examine different aspects of the eye (temporal to nasal, upper to lower lid, etc).

#12 – Light Brightness Knob – Most models have this component on the illumination arm but the Weiss SL 120 has this on the base.  Turn right > brighter

#13 – Locking Knob – May need to unlock to move the base.  Put the lock on if you are moving the whole slit lamp (i.e. in and out of the patient’s room)

PREPARING/POSITIONING

#14 – Table Height Adjustor – To increase patient comfort (and therefore compliance), lower or elevate the table as needed.  You may need to adjust your own chair height accordingly so try to use a stool.

#15 – Power Button – Make sure you’re plugged in!

PERFORMING A SLIT LAMP EXAM:

Step 1: Positioning your patient 

  • Adjust the height of the table to your patient
  • Make sure the patient’s chin is against the forehead strap or you will be unable to focus the slit lamp 
  • Align the lateral canthus of the patient with the red line on the supporting rod of the patient-positioning frame

Step 2: Position yourself

  • Adjust your stool so you can comfortably look in the oculars
  • Adjust the oculars to your interpupillary distance & the focusing ring to your refractive error
  • Pick your magnification (8x or 12x is a good start)

Step 3: Performing Diffuse Illumination

  • Move the illumination arm to 30 degrees off center, preferably to the temporal aspect of the eye you are examining (we usually avoid the nasal aspect because the illumination arm tends to hit the patient’s nose with movement of viewing & illumination arms)
  • Start with a tall & wide (3-8 mm) beam for your initial assessment
  • Adjust the light brightness to patient tolerance
  • Utilizing the white light, globally assess the eye with a systematic approach (i.e. the “Ls & Cs” – lids, lashes, lacrima, lens, limbus, conjunctiva, cornea & chamber [anterior])
  • Stain the eye with fluorescein then examine using the cobalt blue light (assess for corneal abrasions, ulcers, Seidel’s sign, herpes simplex, etc)

Step 4: Perform Direct Focal Illumination

  • Narrow the beam as thin as possible (~1 mm) but keep it tall
  • Maximize the light brightness
  • Move the illumination arm to 60 degrees off center – a curved quadrilateral block should become apparent (aka cornea parallelepiped – see below) – This allows for examination of the depth of the cornea

Photo source: Vislisel, J & Critser, B. Normal cornea. https://webeye.ophth.uiowa.edu/eyeforum/atlas/pages/Normal-Cornea/index.htm. Published June 2, 2015. Accessed July 3, 2020.

  • Next, shorten the beam height (~1 mm x 1 mm).
  • Keep the same max brightness and 60 degree angle.
  • Move your joystick until the space between the lightsource & the parelleliped is overlying the pupil. The black pupil will allow for visualization of cell and flare (see below).

Photo source: Root, T. “Cell and flare” in the eye (video). https://timroot.com/cell-and-flare-in-the-eye-video/. Accessed July 3, 2020.