Whether you’re in a nice quiet exam room or a noisy cafeteria at a school screening, the chances are that your pediatrics patient is going to have the attention span of a small woodland creature. A few of the main concerns with a pediatric patient are to rule out strabismus, amblyopia, and other ambylogenic factors such as anisometropia and media opacities. Luckily for us, all of these things can be at least grossly observed using our handy direct ophthalmoscopes!
These tests are broken up into separate sections for the sake of organization, but in reality they can all be done simultaneously to give you a ton of information in no time!
The Hirschberg test is a way to grossly evaluate ocular alignment. In this case, both you and your patient will be binocular. Sit 40-50cm from your patient and turn on your ophthalmoscope (or penlight), shining it in such a way that both of the patient’s pupils are illuminated and it is centered on the patient’s midline. Have the patient look at the light, noting the location of the small corneal light reflex in relation to the patient’s pupil.
- Tip: You can look through the peephole of your ophthalmoscope and use the red reflex to help delineate the edges of the pupil, especially on a patient with dark irises.
Note the distance between the center of the pupil and the corneal light reflex (CLR) in millimeters. The sign convention is as follows:
- When the CLR is nasal to the center of the pupil, it is assigned a positive value
- When the CLR is temporal to the center of the pupil, it is assigned a negative value
- Expectation: +0.5mm CLR in both eyes (though other values don’t necessarily imply a problem)
- Tip: a pupil in bright light is probably about 2-3mm in diameter; use this to calibrate your estimate of the CLR location
The key here is to notice whether or not the CLR is in the same relative position on each pupil. If they are not equal, the patient may be strabismic.
- Check angle lambda (MLF – described below)
- Do the Bruckner test (described below)
- Do near and far cover test
- Check stereopsis (a global test like the Randot E or the Lang test is a good quick option)
Monocular Light Fixation (MLF, aka Angle Lambda)
This follow-up procedure to the Hirschberg test allows us to:
- Quickly evaluate the angle between the line of sight and pupillary axis (i.e., angle lambda)
- Grossly evaluate fixation and also compare to Hirschberg results for quantifying strabismus
Usually, we expect to see the line of sight displaced 0.5mm nasally from the center of the pupil. The same sign convention is used for MLF as is used for the Hirschberg, so this expected value would be recorded as +0.5mm OD and OS.
Here’s a bullet-point list of the procedure. I like to think of it as a similar set-up to running a finger-counting or finger-wiggle confrontation visual field during entrance skills.
1) Start out by sitting 40-50cm from the patient and aligning your left eye with the patient’s right eye.
2) Close your right eye and position the ophthalmoscope (or penlight) in such a way that the light is on the line of sight for you and your patient (you can look through the scope if needed, as in Hirschberg).
3) Occlude the patient’s left eye and have them look at the light.
4) Note the position of the CLR in relation to the pupil center (in millimeters), just as you did during the Hirschberg test.
5) Do a quick assessment of the patient’s fixation ability (steady or unsteady, jerky, searching, etc).
6) Switch eyes!
It is expected that the CLR will be the same value in the Hirschberg and MLF test. If this is the case, it indicates that the eye positions are the same under monocular and binocular conditions (i.e., the eye did not have to swing into fixation position when binocularity was removed).
If the values for the Hirschberg and MLF are the same:
- Indicates no strabismus
If the Hirschberg reflex is displaced relative to the MLF value for a given eye, it is possible that there is a tropia. The patient will fixate on the MLF test, causing their reflex to look centered and normal. But on the Hirschberg, you will see relative deviation of the reflex. Here’s a quick reference when evaluating the Hirschberg relative to the MLF:
- A CLR shifted temporally will indicate an eso deviation.
- A CLR shifted nasally will indicate an exo deviation.
- A CLR shifted upward will indicate a hypo deviation.
- A CLR shifted downward will indicate a hyper deviation.
Armed with your Hirschberg and MLF results, you’ll have a good idea of the direction of the deviation. For example, a Hirschberg of -0.50mm and an MLF of +0.50mm suggest that the CLR is shifted temporally on the Hirschberg (i.e. there is an eso deviation). A cover test can be used to confirm. The amount of the tropia can be estimated by remembering that 1 mm of displacement is equal to 22 prism diopters of deviation. The displacement (in millimeters) is measured from the CLR position during the MLF test.
Keep in mind that the Hirschberg/MLF is not going to be as comprehensive or specific as a cover test. You’re not testing distance posture at all, and you don’t get information about phorias.
Bruckner Test: Media Assessment, Strab Screening, and Refractive Error Assessment
After the Hirschberg and MLF, it is easy to smoothly move on to do a gross assessment of the media (i.e., cornea, anterior chamber, lens, and vitreous).
Scoot back to about 70cm from the patient. Use the largest light aperture so you can illuminate both eyes, having the patient fixate on the light. Dial in some plus power (get the patient’s face in focus) and look at the pupil through the peephole. At this point, you may be thinking that it is time to evaluate the refractive crescents to get an estimate of the refractive error. For now, though, just pay attention to the red reflex itself.
The key here, as previously, is to look for any asymmetry between the eyes. The red reflex will be asymmetrical if there is:
- Strabismus (in the brighter eye) – you should have some idea about this based on the Hirschberg
- Won’t tell you if the eye is eso or exo, but the Hirschberg/MLF and a cover test should help!
- Media opacity (in the dimmer eye) or retinoblastoma (in the brighter eye)
- Double check: have the patient blink (opacity movement = in tears) and move eyes around (opacity movement suggests floater in the vitreous)
- Anisometropia (with the larger refractive error in the brighter eye)
Now you can pay attention to those crescents! View the red reflex through the peephole, paying close attention to the refractive crescents in the eye. You can determine the type of refractive error, as well as getting a ballpark estimate of the magnitude of the error in each eye.
- Hyperopic crescents will be oriented toward the head of your ophthalmoscope
- Myopic crescents will be towards the handle
- In astigmatism, the red reflex flattens so that it looks more like a straight line than a crescent.
- Get more info by turning the ophthalmoscope 90 degrees so that it is horizontal, and look at the crescents again in the 180 degree meridian
- A crescent filling 50% of the pupil corresponds to roughly +/-1.50 to +/-2.00 D of refractive error, but don’t be shy about dusting off your retinoscope to confirm
If all signs are pointing to a strabismus situation, you can have the patient cover their non-deviated eye and pay attention to how the light reflex looks before and after re-fixation. This is kind of like doing an MLF to follow up on the Hirschberg. As stated previously, a brighter reflex could indicate strabismus in the deviated eye. So, upon re-fixation of that eye under monocular conditions, you should expect to see the reflex become dimmer or duller.
While you’ve got the patient fixating on the light, why not throw in a quick EOM assessment and (if they’ll tolerate it!) take a peek at the posterior pole? Finally, try for a near and far cover test to help quantify any tropia or (at the very least) give you one more bullet point on your list of data!