Hamilton, 31, left in the middle of last Tuesday's loss to the Los Angeles Angels in Anaheim after telling manager Ron Washington he was having trouble seeing.
Hamilton tried to participate in batting practice on Thursday in Anaheim, but had difficulty taking fly balls and was sent back to Arlington for more tests. He did not play at all in this past weekend's three-game series in Seattle.
"Drinking caffeine, coffee in the morning, coffee midday, energy drink before the game, chocolate after the game. All these things were compounding and making it worse and worse," he said.
Hamilton said he didn't have blurry vision.
"My vision was perfect. I don't know how to explain it to you all," he said. "I was fixated on one spot. Call the doctor and let him explain it to you. It was impacting my ability to be ready to play the game."
Texas is 9-7 in games played this season without Hamilton in the lineup.
The five straight games are the most Hamilton has missed consecutively this season. He missed three games in Toronto in late April and early May with back stiffness and another three in Houston with an intestinal virus.
In the game, Adrian Beltre hit a two-run homer in the seventh and singled in the winning run in the ninth.
In other games *
At Chicago, Adam Dunn homered twice, including a clutch three-run shot in the eighth inning, and the White Sox beat the Cleveland Indians, 5-4, to maintain their one-game lead in the AL Central.
Dunn drove an 0-2 pitch from Vinnie Pestano (3-3) over the wall in right-center with runners on the corners and two out in the eighth, putting Chicago ahead, 5-3. Kevin Youkilis kept the inning alive with an infield single before Dunn connected for his 41st homer of the season.
* At Minneapolis, Andy Pettitte turned in another ageless performance with six scoreless innings and the New York Yankees hit four home runs to beat the Twins, 6-3, and extend their AL East lead. The Yankees took a 1 1/2-game edge over Baltimore, which split a doubleheader with Toronto.
After playing three tense, one-run games against Oakland over the weekend, including their startling comeback for a 14-inning win on Saturday, the Yankees enjoyed an easy one for their 10th victory in 12 games.
* At Baltimore, Adam Jones went 4-for-4 with a homer and two RBI, and the Orioles beat the Toronto Blue Jays, 4-1, in the opener of a doubleheader. Ryan Flaherty hit a solo shot for the Orioles.
In the nightcap, J.P. Arencibia broke open a tight game with a seventh-inning grand slam, and the Blue Jays won, 9-5, to earn a doubleheader split and drop the Orioles 1 1/2 games out of first place in the AL East.
* At Detroit, Justin Verlander (16-8) breezed through eight innings and Prince Fielder hit a solo homer, helping the Tigers beat the Kansas City Royals, 6-2. Verlander allowed two runs and nine hits this time, striking out eight without a walk. Jose Valverde pitched the ninth.