Johns Hopkins Health Alert
Diagnosing Cataract Disease
Is your vision blurry, especially at night or in very bright light? It could be an early symptom of cataracts.A cataract is a clouding of the lens of the eye that interferes with clear vision. Unlike a healthy, transparent lens, which focuses light rays precisely onto the retina, a lens clouded by a cataract loses its ability to focus light rays. The light that reaches the retina is scattered and diffuse, causing blurry vision. The amount of vision impairment depends on the size and density of the cataract and where it is located in the lens: the nucleus, cortex or posterior lens capsule. A cataract in the periphery of the cortex, for example, has little effect on vision because it does not impede the passage of light through the center of the lens. On the other hand, a dense nuclear cataract causes severe blurring, interfering primarily with distant vision (at first). A cataract that develops in the posterior capsule has a greater effect on near vision and also causes sensitivity to glare.
Cataracts form painlessly. The most common symptom of a cataract is cloudy or blurry vision. Everything becomes dimmer, as if seen through glasses that need cleaning. Most often, both eyes are affected, though vision is usually worse in one eye than in the other. Other cataract symptoms include glare, halos, poor night vision, a perception that colors are faded or that objects are yellowish and the need for brighter light when reading. In some cases, double vision occurs. This is caused by the passage of light through a lens that has irregular areas of opacity, which can split the rays of light from a single object and focus them on different parts of the retina.
Another symptom of cataracts is the need for frequent changes in eyeglass and contact lens prescriptions. These cataract symptoms can develop rapidly (in a matter of months) or almost imperceptibly, over many years. In the early stages of a nuclear cataract, some people may temporarily have an improvement in vision. For example, a person who previously needed reading glasses for presbyopia is able to read without them. This change, which is referred to as second sight, occurs because the cataract alters the shape of the lens, making it better able to focus on nearby objects. Over time, however, this improvement in vision is lost, and progression of the cataract impairs vision.
Individuals with cortical or posterior subcapsular cataracts often have worse vision in bright light; for example, they may have problems with night driving because of the brightness of oncoming headlights. Bright light causes the pupils to contract and restricts the passage of light to the center of the lens (the part that may be most severely affected by the cataract).
Posted in Vision on October 17, 2006
Reviewed June 2011
Medical Disclaimer: This information is not intended to substitute for the advice of a physician. Click here for additional information: Johns Hopkins Health Alerts Disclaimer
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