A need for glasses leads to blurred vision. With nearsightedness and astigmatism, the distance vision is blurry, but the near vision may be clear. Sometimes this blurring comes out more at night, and there may be the impression of double vision or ghost images. Farsightedness leads to blurry near vision, but the distance may be blurry as well. The need for reading glasses develops especially in the mid-forty's. For more detailed information on the need for glasses and contact lenses, see the section on Optics.

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Cataract

Cataract is a common cause of blurred vision. Cataract occurs commonly in people over 50 years old, but may occur in younger people as well. Usually, with cataract there is a gradual blurring of vision. In some cases, cataract can lead to a change in glasses prescription. There are often other symptoms along with blurring with cataract, including glare problems, problems with night vision, and disturbances in color vision. Cataract does not cause pain or the sensation that something is in the eye. For more information on cataract, see the section Cataract.

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Macular Degeneration

Macular degeneration is a retinal disease that is a common cause of visual loss in the older population, and especially in Caucasians. With mild forms of macular degeneration there may be a blurring of the central vision. In more severe cases, the entire central visual area (for reading, etc.) may be gone. In some cases, distortion in the vision may precede a loss of vision. Distortion in the vision can be recognized when straight lines appear bent, or crooked. A person experiencing this symptom should seek evaluation by an ophthalmologist immediately. Usually, the term "macular degeneration" refers to "age-related macular degeneration", or a retinal disorder occurring primarily in the elderly. Similar conditions occur with ocular histoplasmosis and high degrees of nearsightedness (myopic macular degeneration). For a more detailed discussion, go the the section on Macular Degeneration.

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Macular Edema (swelling)

The "macula" is the part of the retina that perceives our central, or reading, vision. A number of disorders can cause swelling, or edema, of this part of the retina. With macular edema, the vision is usually blurred. Things may appear washed out, and color vision may be reduced. There may be some distortion of the vision as well. Some conditions leading to macular edema include:

• Diabetes - diabetic macular edema is a common problem in diabetes that can lead to permanent visual loss if it is left untreated. For more information on this, go to the section on Diabetic eye disease.

• Cystoid macular edema - this condition, abbreviated CME, is a cystic accumulation of fluid in the macula, which can lead to blurred vision. This occurs sometimes after eye surgery (especially cataract or glaucoma surgery). Sometimes it occurs with inflammatory conditions of the eye (iritis). In a few cases, it occurs spontaneously. Often, CME goes away on its own. An eyedrop may help, and treating any underlying cause (if one can be found) may help as well. It can be a frustrating condition to treat.

• Macular edema can occur with blockages of veins in the eye. If the main vein that drains the retinal blood circulation becomes blocked (central retinal vein occlusion), the macula may become severely swollen. There may be no effective treatment for this. If only a branch of a vein is blocked (branch retinal vein occlusion), the macula may also become swollen. This problem is treatable by laser, if the vision is sufficiently blurred to need treatment. Usually a generous time period is waited before treating this condition (months), since often it goes away on its own.

• Central serous Chorioretinopathy - this condition is common in the younger population (30's to 50's), and can cause variable visual effects. This condition is a dome-like swelling of the retina due to a leakage of fluid from beneath the retina. Some people experience blurred vision, and some distorted vision. Some people describe a circular gray spot in their vision, and some people have disturbed color vision. This condition usually goes away spontaneously with little permanent loss of vision. Some times a laser surgery can help to speed the resolution. Many cases recur.
  
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Aside from the diabetic effects on the retina (Diabetes), a sudden rise in the blood sugar can cause the lens in the eye to become swollen. This usually causes a sometimes severe shift in the glasses prescription toward farsightedness. Thus, a normally nearsighted person may see an improvement in their vision without glasses. However, a person not using glasses, or who is already farsighted, will see a worsening in prescription. Some people find that their distance vision is clearer when viewed through their bifocal! Once the blood sugar is controlled, the glasses prescription will revert back to normal over a period of weeks. Usually both eyes are affected at the same time.

Edema, or swelling, of the cornea occurs when the cornea is unable to keep itself clear, and fluid begins to accumulate within it. The inside lining of the cornea is responsible for keeping it clear, and if this layer is becomes damaged, symptoms of corneal edema may occur. When mild, corneal edema may cause fluctuating or occasionally blurred vision. This may be worst when first opening the eyes after sleeping. One may see rainbows around headlights or streetlights. When severe, corneal edema can substantially blur the vision. Occasionally blisters may form on the surface of the eye (bullae), which can rupture and cause pain, like a corneal abrasion. Causes of corneal edema include:

• A disorder of the inside layer of the cornea (Fuchs' endothelial dystrophy), which can lead to progressively worsening corneal edema over years. This usually affects both eyes.

• Prior eye surgery, such as cataract surgery, can lead to temporary corneal edema. If the cornea was not healthy prior to surgery, an intraocular procedure can cause the cornea to fail, and severe edema can result. Certain types of lens implants (no longer used) are known to cause corneal edema and failure. If the vitreous gel within the eye is allowed to come forward into the front part of the eye (anterior chamber), it can cause corneal edema as well. Severe corneal edema resulting from these causes is often termed "bullous keratopathy".

• Eye trauma can cause corneal damage and edema.

• Acute glaucoma, with very high eye pressure, can cause corneal edema as well as pain. Chronic glaucoma (much more common) usually does not cause this.

• Contact lens overuse can lead to corneal edema, and is a risk factor for infection.

Treatment of corneal edema sometimes depends on its cause. Mild edema can be treated with hypertonic eyedrops and ointment (Muro 128, available over-the-counter). This draws fluid out of the cornea and into the tears, and helps to clear the cornea. More severe edema, especially with blister (bullae) formation, may require corneal transplant to correct. Sometimes a corneal transplant is combined with cataract extraction, a lens implant exchange, or removal of vitreous material, if these are also problems.

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Keratoconus is a disease of the cornea where there is a progressive thinning and bulging of the cornea so that it eventually takes on a cone shape. This generally is not a visible change to the naked eye, but the distortion in the shape of the cornea leads to worsening astigmatism and blurring of vision. Both eyes are usually affected, although one may be much worse than the other. There is no known cause of the disorder, and there is no clear hereditary pattern in most cases. The condition usually stabilizes in early adulthood, although there may be further worsening possible.

There is no cure for the disorder, nor any means to stop its progression. However, the eye is generally otherwise healthy, and glasses (mild disease) and later contact lenses (more severe disease) can greatly improve the vision. In the presence of keratoconus, refractive surgery is contraindicated (not done). In cases where the vision cannot be improved with correction, or if contact lens use is not possible, a corneal transplant is an option. Corneal transplants are generally highly successful after keratoconus, although contact lenses may sometimes still be needed to fully correct the vision. Keratoconus does not recur in a transplant.

An unusual complication of keratoconus is "acute hydrops". When this happens the central cornea suddenly becomes swollen, and the vision becomes blurred and the eye may be painful. With medical treatment, the condition subsides over a period of a few weeks.

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Optic neuritis is an inflammatory condition of the optic nerve. Usually one eye is involved at a time. The vision can become progressively blurrier over a period of hours or days. Sometimes, a blind spot erases the central vision. There may be pain with eye movement. After the vision reaches a low point, it usually gradually recovers over a period of weeks to months. There may be some residual blurred vision, blind spots, loss of color vision, or dimming of vision which persists. Treatment is controversial.

It is currently recommended to have an MRI of the head done with an episode of optic neuritis. This may demonstrate findings which could show risk for development of multiple sclerosis, in the non-pediatric age range. If these findings are found, high dose IV steroids given at the time of an episode of optic neuritis may not only speed the visual recovery, but also delay onset of MS. There are studies being done with other medications which may help as well.

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The optic nerve is subject to losing its blood supply, as is any part of the brain. In the brain, this is called a stroke, or cerebrovascular accident (CVA). In the optic nerve, this is called "ischemic optic neuropathy", or ION. Symptoms of this disorder, which usually occurs in the elderly, is a sudden, painless blurring or loss of vision in one eye. After the initial event, there may be some recovery of vision over a period of weeks. The visual loss can range from mild blurring of vision, to severe loss of vision. Color vision may be affected, and there may be blind spots in the peripheral (side) vision. Some people experience an entire loss of the upper or lower field of vision in one eye. There is an association of this disorder with vascular disease, and it is important to exclude one possible cause of ION, called Temporal Arteritis. Diagnosis and treatment of temporal arteritis may prevent loss of vision in the other eye. Otherwise, there is no effective treatment for ION, except treating any underlying medical problems.

For more information about ischemic optic neuropathy and temporal arteritis, visit the University of Iowa Ophthalmology website.

A number of medications have been associated with the development of an optic neuropathy, leading to reduced visual acuity, blind spots in the peripheral vision, or reduced color vision. Some medications associated with an optic neuropathy include amiodarone, chlorpropamide, ethambutal, and isoniazide. Go to the section on Drugs and the Eye for more information about this. This section also discusses a nutritional optic neuropathy which can develop with alcohol and tobacco use.

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