# Parts of the Human Eye

By Eliya Magesa

Topic: Human Body & Medicine

[Open the interactive Jig](https://ask.jig.com/j/WAujPFydT8Sq)

## Guide

### 1. Meet your eye

This is a model of a human eye, made ten times bigger than life\. A real eyeball is only about 24 millimeters across, about the size of a large grape\. Drag anywhere to turn it around\.

Most of your eyeball is hidden, tucked safely inside a bony socket in your skull\.

### 2. The white and the window

The tough white outer coat is the sclera\. At the front it becomes the cornea, a clear dome that works like a window\. The cornea bends incoming light more than any other part of the eye\.

The cornea does about 70 percent of the eye's focusing\. The lens does the rest\.

### 3. Iris and pupil

The colored ring is the iris, made of tiny muscles\. The black pupil in its middle is not a part at all: it is a hole that lets light in\. Slide the brightness and watch the iris resize the pupil\.

A pupil shrinks to about 2 millimeters in bright light and opens to about 8 millimeters in the dark\.

### 4. Three layers inside

Let's slice the model open\. The wall of the eye has three layers: the white sclera outside, the choroid in the middle, full of blood vessels that feed the eye, and the retina lining the inside\.

### 5. The lens focuses

Behind the pupil hangs the lens, clear and bendy\. The ciliary body holds it on fine fibers\. To see something up close, the lens grows rounder, so the light still lands sharply on the back of the eye\.

### 6. Water and jelly

Behind the cornea is the aqueous humor, a clear watery fluid that keeps the eye firm\. The big space behind the lens is filled with vitreous humor, a clear jelly\. Light passes straight through both\.

Your eye makes fresh aqueous humor all the time and drains the old fluid away\.

### 7. The retina catches light

The retina is a thin lining that turns light into signals\. Its rods work in dim light, and its cones see color and fine detail\. The macula, a small spot at its center, holds a tiny pit called the fovea that gives your sharpest vision\.

Each retina has about 120 million rods but only about 6 million cones\.

### 8. Off to the brain

Signals leave the eye through the optic nerve, a thick cable of nerve fibers that runs to the brain\. Where it leaves, at the optic disc, there are no rods or cones, so each eye has a small blind spot\.

You never notice your blind spots, because your brain fills in the gaps\.

### 9. Light's whole journey

Follow the light: through the cornea, the pupil and the lens, across the clear jelly and onto the retina\. The retina sends signals down the optic nerve, and your brain turns them into the picture you see\.

The picture on your retina is upside down\. Your brain flips it the right way up\.