Hoffer H-5 formula explained

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Physician claims new IOL power calculating formula gives more accurate measurements as it factors in gender-specific differences of the human eye.

By Fred Gebhart; Reviewed by Kenneth J. Hoffer, MD

Los Angeles-There is a new formula to calculate IOL power-The Hoffer H-5, the first fifth generation IOL power formula.

“The Hoffer H-5 adds a new wrinkle to the Holladay 2 formula, introduced by Dr. Jack Holladay in 1996,” said Kenneth J Hoffer, MD, clinical professor of ophthalmology at Jules Stein Eye Institute, University of California, Los Angeles. “I replaced the average axial length measurements Dr. Holladay used with gender and race-specific measurements. The average male eye is 0.50 mm longer than the female eye, so if I were doing a male eye, why would I want to use an average of all human eyes? A more accurate factor will give me a more accurate result.”

Inspiration for the new formula grew out of studies suggesting gender-specific differences in the anatomy of the human eye. Dr. Hoffer analyzed measurements on 212,000 eyes from around the world to determine the formula.

As expected, they found the average male eye is longer than the average female eye. He also found that men have a 0.50 D flatter cornea compared to women, and the anterior chamber in men averages 0.13 mm deeper than in women. These differences were true in all racial categories.

“These are all statistically significant differences,” Dr. Hoffer said. “We also found statistically significant differences in biometry between Caucasian, Latino, Asian-Indian, Oriental, and Middle Eastern eyes. The obvious next step was to a new formula with more accurate factors to produce more accurate power calculations.”

Latest in a series

The H-5 is the fifth generation of advanced theoretic IOL power formulas, Dr. Hoffer said..

The first generation formulas used a constant for the ACD, whereas the second generation began with the 1974 Hoffer formula that used an algorithm for the ACD based on the axial length of the patient’s eye. The third generation was ushered in by the Holladay 1 (1988), which used axial length and added the corneal power measurements to calculate a corneal height plus an individual surgeon factor (SF) to calculate the ACD.

In 1990, the SRK/T formula adjusted the Holladay formula to use of the familiar A-constant rather than a surgeon factor.  In 1993, Dr. Hoffer published the Hoffer Q formula, which uses a tangent of the K-reading and the axial length to predict ACD and calculate the IOL power.

“I did a comparison study hoping the Hoffer Q would be better than the Holladay 1 or the SRK/T,” Dr. Hoffer said. “The Hoffer Q and the Holladay 1 were equally good in the normal range of axial and superior to the SRK/T.

“Then I discovered that the Hoffer Q is definitely superior in small, hyperopic eyes shorter than 22 mm,” he continued. “The SRK/T was better in eyes longer than 26 mm and the Holladay 1 was superior by a great amount in eyes between 24.5 and 26 mm.”

The study had two practical outcomes, he explained. One was a recommendation for the use of the Hoffer Q in eyes shorter than 22 mm, Hoffer Q or Holladay 1 in average eyes 22 to 24.5 mm, Holladay 1 in long eyes 24.5 to 26 mm, and SRK/T in eyes longer than 26 mm.

These findings were statistically proven correct and published in 2010, and remain the criteria recommended by the Royal College of Ophthalmology in the UK.

The second outcome was the introduction of the Holladay 2 formula in 1996. Dr. Holladay described the formula during an oral presentation, but the expected article detailing the calculation was never published. The formula, however, is not entirely unknown.

Dr. Hoffer, and possibly other attendees, photographed Dr. Holladay’s formula slide and he said he found that the formula is based on the logarithm of mean human biometry averages.

Some of the averages he recognized, Dr. Hoffer added, and some he did not. He then decided to rewrite the Holladay 2 using biometric data from his own studies.

“I did another comparison study and found that the Hoffer H was about as accurate as the Holladay 1, the SRK/T, and the Holladay 2,” Dr. Hoffer said. “It had the highest percentage of eyes within a ±0.25 D error, but the MAE and range of error was about the same as the other formulas. I never published it beyond that original poster.”

Holladay has recommended its use.

The Fifth Generation

Fast-forward to 2013 and the Hoffer H-5 using gender- and race-specific biometric averages: an initial study in 90 eyes found a median absolute error (MedAE) of 0.36 D and a range from -1.1 D to +1.47 D.

However, a larger global trial is already under way, Dr. Hoffer said.

Dr. Hoffer said he hopes to collect data on at least several thousand eyes, 100 or more from each of 20 centers with distinct populations from around the world.

Kenneth J. Hoffer, MD

E:  KHofferMD@aol.com

Dr. Hoffer has licensed the H-5 to at least one major instrument manufacturer and is in negotiations with several others.