Corning posted better-than-expected results but its shares pared gains on investor doubts that the company would keep expanding its biggest and most profitable business, LCD glass for flat screen TVs.

Corning said its customers, the Korean panel makers, will pick up production in the fourth quarter and the company's finance chief said retail demand for TVs was improving.

Shares rose 8% on the news but later turned negative and were recently trading 1% higher, after analysts said Corning's management may have been too optimistic on the quarterly conference call.

The company does not give earnings-per-share projections in its forecast or a concrete revenue target.

''The company appears to be sliding down a slippery glass slope as the economy softens,'' said Ticonderoga Securities analyst Brian White.

White added that Corning's LCD business will have trouble growing because global TV sales will not rebound.

''When I look at Corning, I look big picture, and the LCD glass market may stop growing in the next three years.''

Another analyst, Srinivasan Sundararajan from Oppenheimer & Co, also said Corning's executives were too positive, considering most TV manufacturers have slashed their TV sales forecasts.

''Even though Corning had upbeat comments on the call, the reality is there is not much demand for flat panels,'' he said.

The German drugs and chemicals group Merck KGaA which makes liquid crystal for display screens, cut the top end of its 2011 sales forecast on Wednesday because of weakness in the next two or three quarters in the flat screen industry.

Corning, which makes the liquid crystal display glass used in flat-screen TVs, said that Korean manufacturers Samsung and LG Electronics will boost their production in the holiday quarter. Weak demand for televisions has been hitting panel prices in recent quarters.

The upbeat comments on Korea were not expected by investors and initially moved Corning's share price on Wednesday, Corning's chief financial officer said.

''The fact we said Korea would be up was a surprise to people,'' said Corning's finance chief, Jim Flaws, in an interview.

Flaws also said that retail demand for TVs was improving and that panel makers would soon be buying more glass after months of inventory reductions. He said retail demand was up 13% this year.

''As retail, TV sales have been doing fine. We think we will get through that inventory reduction and assuming that retail continues at the pace we've seen this year, it would give us volume increases,'' Flaws said.

Corning on Wednesday said its earnings received a boost from the strong Japanese yen, and Flaws said the strong currency ''will probably help us again in the upcoming quarter.''

Besides LCD glass, Corning makes resilient thin cover glass for touch-screen devices such as smartphones and tablets. That segment increased 90% to $299 million in the quarter.

Corning reported earnings per share of 51 cents, or $811 million, up from 50 cents per share, or $785 million, according to Thomson Reuters I/B/E/S. Sales increased 30% to $2.08 billion, which was ahead of analysts' estimates of $2.02 billion.