Eye shapes play a crucial role in vision. The eye works by focusing light as it passes through the cornea and the crystalline lens. The light travels through the vitreous humour, a clear gel filling the inside of the eye, and hits the retina at the back of the eye. If everything is functioning properly, the light is clearly focused on the retina, allowing rods and cones that pick up light to pass on a clear image to the optic nerve and then to the visual cortex of the brain. The way the cornea and lens focus light works on the assumption that the eye is a certain shape so that the distance from the lens to the retina is a certain length. When these shapes are off, it causes refractive errors like myopia, hyperopia, and astigmatism.
Myopia or Nearsightedness
Myopia, the most common vision problem across the world, is caused by abnormal eye shape. Generally myopic eyes are longer than normal—the distance from the cornea to the retina is greater than in a normal eye. This causes light to converge in focus too soon, before hitting the retina, so by the time it hits the retina it is blurry. Nearsighted patients can usually see close objects clearly but have poor distance vision.
Hyperopia or Farsightedness
Hyperopia is the opposite of myopia—the eye is too short. The point where light would converge in focus in the eye is behind the cornea, so the light does not have enough distance to travel. This prevents farsighted patients from clearly focusing on close objects.
While hyperopia and myopia are caused by overall eye shapes, astigmatism is caused by the shape of the cornea itself. Normal corneas are curved equally in all directions, like a section of the outside of a ball. Astigmatic corneas are curved irregularly, like the surface of a football. This prevents light in the eye from focusing at a single point and causes distorted vision.
LASIK and Eye Shapes
LASIK treats these problems not by reshaping the eye, but rather by reshaping the cornea to make up for the shape of the eye. For myopic eyes, the cornea is flattened, causing light to converge at the cornea instead of before it. LASIK for hyperopia does the opposite—the curvature of the cornea is increased to focus light closer. For astigmatism, the curve is simply evened out to provide clear focus. The shape of your eyes determines how good your vision is naturally. Fortunately, LASIK can correct irregularly shaped eyes.