Chuck Thompson, the voice of Orioles baseball and Colts football for generations of Marylanders, is undergoing treatment for an optical disease that could bring to a close his broadcasting career.

Thompson, who will be 79 next month, is suffering from macular degeneration, a leading cause of blindness among the elderly, that has limited his vision to the point where he can neither read documents nor do baseball play-by-play, because he can't see the ball.

As a result, Thompson's duties on Orioles games this season have been limited to commentary, a role he will fill this weekend in New York, while Fred Manfra is doing Kentucky Derby broadcasts for ABC Radio.

"I have parts of sight, but I don't have the ability to read. I can look out my window and see trees and I can see my grandchildren and my wife," said Thompson. "There's one minor problem and we hope that it can be corrected."

Thompson, who said he has felt the effects of the disease for the past two years, is undergoing a new, experimental form of treatment called photodynamic therapy at the Johns Hopkins Wilmer Eye Institute. The treatment may either slow the progress of the disease or help him to see better.

In the "wet" form of macular degeneration, which Thompson has, tiny capillaries grow behind the macula, the portion of the retina that provides central vision. When those vessels burst, the blood from them destroys light-sensing nerve cells and damages a person's sight.

Thompson said the disease causes no pain, headaches or side effects, but has the effect of making it difficult for him to distinguish word endings or to follow a plane across the sky or a putt across the green.

Thompson said he can see stop signs, but not when they are surrounded by trees and other vegetation, and while the ailment has improved his night vision, one of the unfortunate casualties of the disease is that he has been unable to complete the audio version of his book, "Ain't the Beer Cold."

"The stop sign just blends right into the foliage. Yellow lines on the road just seem to split right up the middle, as do telegraph poles," said Thompson, whose brother also suffers from the ailment.

The photodynamic therapy treatment that Thompson is undergoing involves the infusion of a drug, verteporfin, into the bloodstream. The drug looks for and identifies the abnormal capillaries, then, using a low-power laser, a doctor starts a chemical reaction that essentially seals off the vessels and causes them to dry up.

Thompson, who underwent the therapy earlier this year, said the evaluation period, which was originally thought to be about seven weeks, may now be as long as three months.

The doctors "are not positive that it will have any effect and they are anxious to see what the result will be, as am I. It may work for some people and not for others," said Thompson. "If anything good comes of this, I'm hoping that my experience can be helpful to others who have this and aren't seeking treatment."

Thompson has been a mainstay of Baltimore radio and television since he began broadcasting Orioles minor-league games in 1949, and his catch phrases, "Go to war, Miss Agnes," and "Ain't the Beer Cold," are indelibly stamped in the memories of area fans.

He received the Ford Frick Award from the Baseball Hall of Fame in 1993, which while not technically signifying induction into the Hall, is the highest honor a baseball announcer can receive. Besides the Orioles, Thompson, and former WBAL broadcaster Vince Bagli, were the voices of the Colts, and area football fans will recall his call of Alan Ameche's touchdown plunge in the overtime of the 1958 NFL championship game between the Colts and the New York Giants.

In recent years, Thompson, who will work alongside Jim Hunter on Friday and Saturday, has done a limited schedule of Orioles games for WBAL (1090 AM), the team's flagship station, and station manager Jeff Beauchamp said he's content to let Thompson work at his own pace.

"We made it clear to Chuck when we entered into this last deal that he could do whatever he felt comfortable with," Beauchamp said. "If he wanted to do color, that's fine with us. He's an icon and we want him to be a part of our broadcast in whatever way is best for him."

Clarification:

The Sun reported that Orioles radio announcer Chuck Thompson was undergoing "new, experimental therapy" to treat the eye disease macular degeneration.

When Thompson's treatment began earlier this year, the therapy was permitted as part of an experimental study. Since then, on April 12, the Food and Drug Administration approved verteporfin, the drug involved in the therapy, making it no longer experimental.