# Axial Elongation in Myopia Progression How the eyeball lengthens in myopia, and how close work, daylight and the retina's focus signals shape that growth over time\. By nimble\-comet\-cd7773bc Topic: Human Body & Medicine [Open the interactive Jig](https://ask.jig.com/j/3wIkoOgZrByo) ## Transcript ### 1. An eye that keeps growing This model eye is sliced open so you can see inside\. Light enters through the clear front and lands on the retina, the thin light\-sensing layer at the back\. In myopia, or short\-sightedness, the eyeball slowly grows too long from front to back\. Drag anywhere to turn the model\. ### 2. Sharp sight needs the right length The clear cornea and the lens bend light so it meets at one point\. When that point lands exactly on the retina, faraway things look sharp\. An adult eye is about 23\.5 millimetres long, roughly the width of a large coin\. A newborn eye is only about 17 mm long\. ### 3. The eye steers its own growth A child's eye grows, and the retina acts like a guide\. If light would meet behind the retina, the eye takes that as a "grow" signal\. If it meets in front, growth slows\. Watch a young eye grow until its focus lands just right\. Scientists call this tuning emmetropisation\. ### 4. Up close, all day long Reading or using a screen close up for hours asks the eye to focus hard\. Its focusing often falls a little short, so the sharpest image sits slightly behind the retina\. That can send the same "grow" signal, again and again\. The model exaggerates distances so you can see the rays\. ### 5. Daylight sends a calming signal Bright light makes the retina release more dopamine, a chemical messenger that helps hold back growth\. Slide from indoors to outdoors and watch the green sparks of dopamine rise as the "grow" pulses fade\. Daylight outside is usually many times brighter than indoor light\. ### 6. A message through the wall The "grow" message passes from the retina, through the choroid, a spongy layer full of blood vessels, to the sclera, the tough white outer wall\. The sclera then remodels: its tight fibres loosen and the wall gets thinner\. The choroid also tends to thin as myopia advances\. ### 7. The eye stretches longer Over years, the softened back of the eye stretches, mostly from front to back\. Press the button to fast\-forward and watch the length grow\. Now light meets in front of the retina, so faraway things look blurry\. A progressing child's eye can grow about 0\.3 mm a year\. The model exaggerates the stretch\. ### 8. Clear sight, and gentler growth A concave glasses lens spreads the light a little, so it meets on the retina again\. Glasses make the world sharp, but they do not shorten the eye\. Time outdoors and breaks from close work help keep growth gentle\. About 1 mm of extra length adds roughly 3 dioptres, the units used for glasses strength\.