A cataract is a clouding of the eye's natural, clear lens. Think of it as a clear window that slowly becomes frosted. This clouding scatters light, preventing a sharp image from reaching the retina. It is most commonly related to aging. However, some forms of congenital cataract are seen in children.
Refractive error means that your eye does not focus light ideally onto the retina, resulting in a blurred image on the retina. This condition is not a disease, but a common problem with light focusing. Its main types include myopia (nearsightedness: nearby objects are clear while distant objects appear blurry), hyperopia (farsightedness: distance vision may be clearer than near vision), and astigmatism (vision is blurry at all distances due to an irregularly shaped cornea).
Night blindness is a symptom, not a disease. It means your eyes have trouble adapting to low light. This is often due to a problem with the rod cells in your retina, which are responsible for night and peripheral vision.
Most color blindness is not complete blindness to color, but a difficulty telling certain colors apart. It is usually an inherited condition (more common in males) present from birth. It happens when certain light-sensitive cone cells in your retina don't work properly. The most common type is trouble distinguishing reds from greens.
ROP is a disease that affects premature infants. In the womb, the retinal blood vessels grow late in pregnancy. When a baby is born very early, this normal growth is interrupted. After birth, abnormal, fragile blood vessels may begin to grow in the retina. These vessels can leak and scar, potentially pulling the retina off (detachment).
A retinal detachment is a medical emergency. It occurs when the retina peels away from the back wall of the eye, like wallpaper bubbling off a wall. When detached, the retina cannot function, leading to vision loss.
A retinal hemorrhage means there is bleeding inside the layers of your retina. Think of it as a bruise on the light-sensitive film of your eye. It is a sign of an underlying problem, not a disease itself.
The inside of your eye is filled with a clear, gel-like substance called the vitreous. As we age, this gel naturally becomes more liquid and can pull away from the back surface of the eye. This separation is a PVD. It is a very common, age-related event and is not, by itself, dangerous.
AMD affects the macula—the tiny central part of your retina responsible for sharp, "straight-ahead" vision used for reading, driving, and recognizing faces. The rest of your side vision usually remains intact. In "Dry" AMD (the more common type), the macular tissue thins and breaks down. In "Wet" AMD, abnormal, leaky blood vessels grow under the macula and can cause rapid damage.