Categories

Today’s blog was supposed to be about toric lenses. I found, however, (I came from the future at the end of this blog to write this first part here) that making sense of this topic is kind of like house cleaning. Because usually when I’m cleaning my home, I find that the only way to get the job done right is by continually starting further back than I planned. I’ll start to vacuum, then realize I should clean the counters first. But when I start on the counters, I find a glass or plate and realize I should do the dishes first. The dishes in the dishwasher are clean? Okay, I’ll start by just putting those away real quick… till eventually I’m an hour in on a task that I won’t start for another 30 minutes.

Let’s Get Astimatism Right

That’s what happened with this blog. I started with toric IOLs, then realized I should talk about toric lenses in general. Wait, no, before that we should define what toric means. Actually, that won’t matter till we get a good explanation about astigmatism. Eventually, I gave up on trying to fit all that into a novella-sized blog because I realized the only way for us to get this right is to start further back than I planned. So Part I here is going to make sure we get astigmatism right.

Everyone has heard of astigmatism, but almost no one knows what it does, like the Kardashians. Personally, I blame the ubiquitous football-astigmatism metaphor. I was told my eye is shaped like a football for years and didn’t understand why until ophthalmology residency. (Quick aside: I knew what a football was despite my general nerdiness. I had cool, normal brothers. They got a football for Christmas the same year that I got – and I swear this is true – desk supplies. And I remember being so excited! Just over the moon about my gifts that year. I was 10 at the time.) Anyway, matching a football up with eye shape and blurry vision never clicked.

A better way to think about astigmatism is imagining a piece of plexiglass two feet high and two feet wide. Imagine holding that gently by the right and left side. The image through this flat plexiglass: clear, undistorted, and normal. Now imagine just lightly squeezing in on both sides with your hands. The plexiglass is going to curve a bit between your hands. A lizard walking across it from one hand to the other now has a subtle little plexiglass hill to climb up and then back down. The image through it now: blurry, distorted, and worse.

That squeeze created astigmatism in the plexiglass. It happened because now there’s a curve from right to left across it, but no curve from top to bottom (the lizard has the same no-hill walk from top to bottom both before and after we squeeze the glass from the sides). We can go even further and see where the name “astigmatism” comes from.

A-Stigmatism

A stigma is a dot or a point (that’s where the name stigmata comes from if you watch scary movies or are a big St. Francis of Assisi fan). Adding an “a” as a prefix before it just makes it mean “not.” So a-stigma means it’s not a dot. When you shine a laser pointer through the flat plexiglass, you’ll see a dot on the wall. When you shine it through the squeezed version, you’ll see a smeared, amorphous laser light hit the wall – not a dot. A-stigmatism.

This is exactly what happens for people with astigmatism. The only difference is that, instead of a piece of plexiglass, your eye has a small, clear, dome on the front of it (the cornea). But whether it’s a big, flat window of plexiglass, or a small, domed window of cornea, astigmatism works the same. A little “squeeze” on the side creates a steep curve where you’re squeezing, and a flatter curve perpendicular to it.

One last bit before we go… the fact that the cornea is so small and domed makes it a super powerful focusing lens. Equivalent to a +45.00(!) pair of readers. That’s why even small amounts of astigmatism cause noticeable blur. WIth a lens that powerful, just the slightest imperfection of shape has a big effect. But good news! Next blog, we get to talk about a great way to fix that! See you there.