Last week, in Part 1 of this series, I introduced a couple basic components of a pediatric eye exam – namely communication and visual acuities. Though these are both huge concepts, they barely scratch the surface of everything that occurs in an infant eye exam.
Ready for Part 2? Let’s go.
So, whether you realize it or not, there are a lot of little components to any eye exam that it may be easy to sweep under the rug. In today’s post, I’ll dive into each of those, and how they vary in a kiddo’s exam!
So, in adults, this is often tested by what’s called a cover test. I won’t get into all the details because the specifics aren’t really necessary in the context of this discussion. The basic concept though, is that I, as the doctor, cover each of your eyes individually in a specific pattern while you focus on either a distance or near target. If one eye wasn’t initially on the target, covering the other allows it to take up fixation. Likewise, alternating between eyes reveals the preferred position of the eyes when they’re not working together.
Some days, this is honestly hard enough on an adult. Trying it in an infant? That’s essentially impossible. (First, they don’t understand what you’re telling them to do. And even if they do understand, have you ever tried to get a child to look at a single object for more than a couple of seconds?!)
So, we switch up the technique.
One of the primary determinants of ocular alignment is simply shining a light at the kiddo and seeing where the reflexes are on each cornea. If they’re the same? Great! The eyes are (at least grossly) aligned. If they’re different? Then my job is to determine which eye is misaligned, and by how much (either by estimating distance or measuring with prism).
Though I haven’t gone over this test/technique in my “Why Does My Eye Doctor…” series yet, this is a test I’m sure every one of you (who has had an eye exam) has experienced. It’s the part of the exam where the doctor says “okay, follow my light…” and then moves the light up and down and side to side.
Spoiler alert: They’re looking at your eye movements.
Sometimes this technique works in little ones, but not all children are obsessed with lights, and getting them to consistently follow a single target? That can be difficult.
What’s to be done?
Simple. Whatever it takes.
Since this isn’t a test of side vision, most anything can be used to make sure that the kiddo can fully move their eyes in all directions – bright objects, flashing lights (provided they don’t have seizures triggered by lights), sounds, touch, faces – you name it. It’s all about finding whatever the child will look at in the moment and getting them to find it with their eyes.
Side vision, or peripheral vision, testing, however, is a whole different game.
In the adult population, there are several methods of testing visual fields. The simplest generally involves having to accurately assess the number of fingers presented in each portion of the visual field in both eyes. Most people, however, are probably more familiar with the “clicky-light” test, where a light flashes on in different parts of your vision, and you respond by clicking the provided button.
Both of these methods tend to be a bit difficult with infants and other young children.
However, instead of using any means available, testing in this case can only involve vision – in other words, no sound or touch allowed.
From that point, however, there are many potential visual targets, from those long flowers, to pens, to bright pool toys, to rubber chickens (my personal favorite)… the list could go on for ages.
Optimally, these targets are slowly brought in from the far side (non-seeing range), until the child responds – normally by turning or looking towards the object. This strategy is then repeated in all fields of gaze (there are 6 for each eye).
First off, depth perception is a deep topic.
While depth perception could be an entire post of its own, the basics are:
while there are some clues to depth that can be determined just by using one eye, true depth perception requires the central portion of both eyes to be looking directly at the target.
In adults, this is typically tested with those 3D book things, where you’re asked to tell what shapes you see and what circles “jump out” at you. It’s not always easy.
This test is even harder with a child that can’t exactly express either of these answers. So, we make it easier.
Similar to testing visual function, one of my favorite ways to assess depth perception in children is by using a test with one blank card, and one card with a face (that can only be seen with polarized glasses and intact depth perception). When I hold up the two cards at the same time, I watch to see which one the child looks at. If they consistently look at the one with the face, they can probably see it. If they randomly look at either, well, there’s no guarantee. This test continues, with each face card getting harder and harder to see, until the responses appear completely random.
However, not all offices have this test. In such cases, small amounts of prism can be used to determine if both eyes are working together, by placing a prism in front of one eye, and then watching the resulting eye movements (prisms move the image).
Annnd I think that’s about enough pediatric eye exam techniques for one day!