Allergan Agrees to Sell Humphrey Subsidiary : Medical technology: Carl Zeiss, a German-based international supplier of optical and electronic products, plans to purchase the company, which makes ophthalmic diagnostic equipment.

Allergan Inc. said Friday that it had agreed to sell its diagnostic-instrument subsidiary, Allergan Humphrey, to the German-based Carl Zeiss for an undisclosed sum.

Analysts valued the sale at between $50 million and $70 million.

Sales at Allergan Humphrey have been declining since 1988, and although Allergan said the unit was not losing money, profit margins were slim. The company said it would use proceeds from the sale to reduce debt and strengthen its core businesses of developing pharmaceutical and consumer products for eye and skin care.

Allergan’s shares fell 25 cents to $20.25 a share in New York Stock Exchange trading Friday. Despite the slip, several stock analysts said the Humphrey division was not a natural fit with Allergan’s other products, and its sale would help the company’s earnings.

Allergan Humphrey makes microprocessor-based ophthalmic diagnostic equipment, including a device to diagnose glaucoma and an automated refractor to evaluate vision.

In 1990, the subsidiary contributed $79.8 million to Allergan’s total sales of $883.9 million. But sales have been on a downward trend--from $84.9 million in 1988 to $82.7 million in 1989. For the first six months of 1991, sales totaled only $30.8 million.

“This was an operation that was not growing,” said James P. Keeney, pharmaceutical analyst at Mabon Securities in New York. “It had positive earnings, but it was only generating half the margin of the business as a whole.”

Keeney estimated that profit margins were only 5% for the division, compared to 10% for the company as a whole.

Keeney estimated the purchase price at roughly $52 million. Analyst John J. Girton of the Van Kasper & Co. brokerage in San Francisco put the figure at roughly $50 million to $70 million.

Carl Zeiss, through its Thornwood, N.Y., subsidiary, said it would have no comment on the acquisition until it passes regulatory muster. Carl Zeiss is an international supplier of optical and electronic products.

Under the deal, Allergan retains the rights to its technology for phacoemulsification equipment, devices that suck out defective lenses during cataract surgery. Humphrey will now manufacture the device, but two companies will jointly market it.