June 2007

 

OPHTHALMOLOGY NEWS

 

Lens prescriptions aid forensic identifications


by Matt Young EyeWorld Contributing Editor

 

 

Prescription eyewear could help investigators identify missing persons or catch criminals

Although lens prescriptions are distinctive, DNA analysis and odontology remain the cornerstones of forensic science. “Currently, when lens prescriptions are used in forensic identifications, investigators are constrained to a simple ‘match’ or ‘no match’ judgment with an antemortem prescription,” wrote Gregory E. Berg, forensic anthropologist, Joint POW/MIA Accounting Command (JPAC), Central Identification Lab, Hickam Air Force Base, Hawaii. “It is not possible to evaluate the strength of the conclusion, or rather, the potential or real error rates associated with the conclusion.”

But a new scientific article by Mr. Berg published in the March 2007 issue of the Journal of Forensic Science suggests personal identification based on prescription eyewear could become a new tool for investigators. The article provides a fascinating glimpse into how optical refractive errors could be used in the future to identify missing persons or even catch killers.

Expanding the scope of visual identity

Mr. Berg analyzed three databases that compiled more than 385,000 individual prescriptions. He said the databases “allow forensic analysts to easily determine the strength of individuation of a spectacle match to antemortem records by calculating the frequency at which the observed prescription occurs in various U.S. populations.”

The databases were used in two case studies to show their ability to enhance personal identification in cases in which pieces of eyeglasses are recovered. Researchers also used a new computer program called OptoSearch (JPAC, Hawaii) in conjunction with the databases to determine the rarity of personal optical prescriptions.

“By tabulating the number of occurrences of a known refraction error within a population, objective statistics can be generated to evaluate the strength of a match between that refraction error and an individual’s antemortem medical record,” Mr. Berg wrote. While the program might not lead to identification with 100% certainty, it could create a short list of possible individuals.

Case studies

Using OptoSearch and the databases, researchers analyzed two cases to determine two individuals’ identification. The first case analyzed eyewear fragments to identify one of two individuals involved in a small observer plane crash that took place in a Vietnamese jungle in 1968. The two aircraft crew members were reported missing in action.

In 2000, excavations at the site provided clues to what happened, including aircraft artifacts, possible human remains, and three sunglass lens fragments. Two of these lens fragments were sphere –0.5 with no astigmatism correction; the third fragment was too tiny for examination. Records indicated that the pilot had refractive error; the co-pilot did not. What’s more, the lens fragments found and identified matched the prescription for the pilot’s left eye. Further analysis showed that the left eye’s prescription is relatively common, occurring at frequencies of 2%, 0.2%, and 1% in the databases used. Nonetheless, the information gathered from the lens fragments suggested that the pilot was very likely at the scene of the crash and that the co-pilot was not.

The second case showed how lens analysis could be even more useful. In 1967, a U.S. military F-105 pilot crashed in Southeast Asia. Decades later, during the 1990s, attempts were made to identify the pilot. Witnesses suggested the pilot’s body was buried near the crash site. The burial ground was excavated, and remains, the flight suit and other flight gear, and sunglass lens fragments were found at the scene of the crash. The prescription of the lenses was sphere –0.50, cylinder –0.25, and axis unreadable. The fragments matched the missing pilot’s left eye. The prescription was also compared to one of the databases, which came from the Department of Defense (DOD). “The strength of match frequencies indicates that another individual having the exact same left eye prescription (not including axis) is c. 6/1000,” Mr. Berg wrote “The sunglass fragments played a minor supporting role in the identification, but the method proposed here demonstrates that optical wear can definitively increase the confidence of the identification based on the strength of the match to the pilot’s antemortem records.”

Mr. Berg suggested three areas in which eyewear analysis could be particularly useful. First, optical lenses can place people at crime scenes and eliminate others. Second, the prescription frequency indicates the rarity of the person in question, and assists with accurate identification. Third, the frequency of refractive error can be combined with other identification methods to heighten the accuracy of identification.

An ophthalmologist’s perspective

Mark Packer, M.D., clinical associate professor, Casey Eye Institute, Oregon Health & Science University, Portland, said prescriptions are not completely unique and certainly not fail-safe. There is also a range of error in the grinding of glasses and production of contact lenses. Pupillary diameter, however, could be one future factor for analysis that could lead to better personal identification. When opticians make eyeglas-ses, they measure the distance from one pupil to the other. They are also supposed to set the optical center of each lens right over the pupil. These numerical values could also assist in investigations.

“And if you’re really being Sherlock Holmes, you could figure in the cost of the frames to figure out the socioeconomic class of the person,” Dr. Packer said.

Editors’ note: Mr. Berg has no financial interests related to his study. Dr. Packer has no financial interests related to his comments.

Contact Information

Berg: greg.berg@ds.jpac.pacom.mil

Packer: 541-687-2110, mpacker@finemd.com

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