Thanks to Australian innovation, it’s only a matter of time before objective perimetry removes much of the frustration associated with subjective perimetry – for patient and practitioner alike.
In keeping with my promise to feature leaders in the Australian and New Zealand eye care fraternity, I recently discovered a legend in our midst who may be unfamiliar to many.
We’re fortunate Ted’s path led him into working on human vision in health and disease…
Professor Ted Maddess and his team patented and developed Frequency Doubling Technology (FDT) perimetry. The first generation FDT was brought to the market in 1997 by Welch Allyn in collaboration with Zeiss. It later evolved into the Zeiss Matrix device, with printouts more familiar to users of Zeiss’ Humphrey field analyser. My colleagues and I used three FDT instruments over 20 years, screening well over a hundred thousand patients, with great results.
Prof Maddess completed his undergraduate degree at the University of British Columbia where he became fascinated with the diverse optical designs of eyes. In 1981 he moved to the Australian National University to do a PhD on insect vision but ended up working on nonlinear adaptive mechanisms in the mammalian visual cortex. Although intending to continue that work at the John Curtin School of Medical Research, he instead became interested in a retinal adaptation mechanism to invent a new stimulus for mapping visual fields.
Prof Maddess commented, “My initial interest in the optical designs of invertebrate eyes led me to examine how visual systems squeeze real-time visual information into brains of very limited information capacity. My subsequent research into adaptive neural processing led to new glaucoma detection devices.”
Ted is a recent past director of the Australian Research Council’s Vision Centre, and some of his team’s work includes the adaptive dynamics of following eye movements, the processing of texture and brightness, as well as methods for diagnosing neurological disorders. We’re fortunate Ted’s path led him into working on human vision in health and disease.
KILL ME NOW…
If you’ve ever had to perform repeat glaucoma fields on a 94 year old patient with poor vision, motor control issues, incontinence and dementia, you’ll know it’s no walk in the park. Apart from the frustration, we’re really never sure if we’re looking at progressive glaucoma damage or poor subjective patient responses. Fortunately, there’s hope on the horizon – Ted and his team have developed a breakthrough noncontact, objective perimeter which exploits ‘multifocal pupillography’.
The resultant platform is called the ‘objectiveField analyser’ (OFA) and is being developed and commercialised by Konan Medical, USA – Konan’s website says it has cleared the FDA 510(k) hurdle and is ‘coming soon’.
The OFA has been shown to have value in glaucoma, diabetic retinopathy, macular degeneration, and multiple sclerosis. Its objective nature removes many of the problems associated with subjective responses in standard perimetry.
Another challenge we face with standard perimetry is setting up the correct spectacle Rx, in order for the patient to optically resolve the tiny flashing stimuli at the test distance. This can be tricky and time consuming.
On this, Ted shared the following insight, “One feature of OFA is that the stimuli contain no spatial frequencies above two cycles per degree. So, it is highly tolerant of mis-refraction (a bit like FDT). It does have a small set of trial lenses in steps of 3D. The operator enters the person’s script and the device recommends a pair of lenses. The lenses are not at the exact spectacle distance so there can be a little magnification or minification (a few percent at worst), therefore the algorithm tries to recommend a pair of lenses that are the same power. This helps people fuse the stimuli (and) there are other powerful fusional cues, which also help with fixation.”
You may gather from this that the OFA operates binocularly, measuring each eye’s visual field simultaneously, thus further saving time. Remarkable.
To get your head around multifocal pupillography and how the OFA works, check out vimeo.com/305851668