Autofluorescence Testing and Vision Loss
Autofluorescence Testing May Detect Retinal Damage Before Vision Loss Occurs
Many eye disorders that can lead to loss of vision are often detected after injury to vision has occurred. Visual field analysis is helpful in detecting existing damage but is not useful in detecting early dysfunction. Researchers at the University of Michigan have adapted
a novel, non-invasive method to measure retinal cell injury and have used it to determine if it is a more sensitive way to detect early vision loss.
The authors were interested in finding a non-invasive method that would detect retinal cell injury in patients with idiopathic intracranial hypertension (IIH) at a very early stage before visual damage occurred. Previous research conducted on animal myocardial cells revealed that when cells were severely stressed, a mitochrondrial protein (favoprotein) showed a unique property called autofluorescence—it glows— prior to actual cell death (apoptosis).
Although mitochrondrial favoprotein autoflourescence (AF) testing had not been done on human cells, the authors believed that it could be used to detect early metabolic stress in retinal cells and thus be a very early indicator of potential vision loss.
To prove their hypothesis, the researchers selected six women recently diagnosed and untreated with IIH. Each patient had a visual acuity of 20/30 or better and each underwent automated visual field testing (perimetry). The patients had either no field defects or subtle field defects. All patients experienced varying degrees of blurred vision or symptoms of transient visual obscurations. All six patients had varying degrees of swollen optic nerves (papilledema). Six age matched healthy women served as controls subjects.
The results obtained from each group were ultimately compared to determine the outcome of testing.The researchers used a specially-designed camera system that had been fitted with excitation and emission filters that were connected to a computer with customized imaging software. The software enabled the measurement of AF, which, in turn, might reveal early retinal cell dysfunction.
The test was done by dilating each subject’s pupils and using the camera system to record three small images from each eye. The total eye test time took less than six minutes for each patient.
The results indicated that the worse eye in each IIH patient (as evidenced by the clinical degree of papilledema and visual field abnormality) showed higher levels of AF than the patients’ less affected eye. In the IIH patients, the most affected eye showed an average of 60% higher AF than the patients’ least affected eye.The control group did not show any difference between eyes.
While an ophthalmologist with an ophthalmoscope can observe papilledema in an IIH patient, such examination is often not diagnostic for visual dysfunction.Visual impairment is detected by subjective visual field analysis, and although this is considered the most sensitive of tests, early visual dysfunction may not be detected.
The non-invasive AF measurement techniques used by the authors, show significant promise in the early detection of impending vision loss, even before detection by conventional visual field studies.
Of interest would be a study done on patients with confirmed IIH with high opening pressures on spinal tap, and classical signs and symptoms of elevated intracranial pressures, but without papilledema and field abnormalities. (Often the diagnosis is unclear or withheld because of the absence of observable papilledema.)
Would AF testing reveal that despite the lack of observable papilledema, retinal cells were under metabolic stress? And if so, would ultrasonic retrobulbar optic nerve diameters be normal or increased in cases of AF positive testing, normal visual field studies and absence of papilledema? In IIH cases without papilledema, would AF positive findings confirm the IIH diagnosis? Since the test does not require the patient’s active participation, could AF testing also be used in emergency settings of acute traumatic intracranial hypertension as a means of non-invasively detecting high CSF pressure?
The authors of this paper have opened a new area for important investigation of visual function in patients with intracranial hypertension.
Note: This feature is adapted from an article that ran in the Spring 2008 issue of our Insight newsletter
To Read More:
Favoprotein Autofluorescence Detection of Early Ocular Dysfunction
Elner VN, Park S, Cornblath W, Hackel R, Petty HR
Archives of Ophthalmology. 2008 Feb; 126(2):259-60