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Minimally invasive diagnostic tools speed the processes of screening, diagnosis
As manufacturers strive for fast results with improved diagnostic accuracy and reproducibility, ophthalmologists reap the rewards.
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Minimally invasive surgery is the trend in ophthalmology as well as other areas of medicine. Minimally invasive diagnostic techniques, too, are increasingly important. Especially in screening for glaucoma and other diseases, the ability to move patients through quickly with accurate results is a clinical priority.
The ideal screening method for detecting glaucoma has yet to be determined, but recent advances in testing algorithms allow glaucoma exams to be done in a fraction of the time it takes for full perimetry.
Screening for glaucoma
In a study that appeared recently in the American Journal of Ophthalmology, researchers in Tokyo found frequency-doubling technology (FDT) perimetry to accurately detect disease in 83.3% of patients with early-stage glaucoma and 100% of patients with moderate or advanced glaucoma.
According to the Glaucoma Screening Study Group, 14,814 workers of a median age of 41 years were screened for glaucoma in hospitals and clinics throughout Japan. Investigators said that this form of testing offered many advantages for screening large groups, because it was simple to use with no need to correct refraction. In addition, the diagnostic system was lightweight and portable, quick and inexpensive, and did not require an expert technician to carry out the examination.
While researchers believe that visual field testing with FDT perimetry is “applicable to population-based, large-scale surveillance for glaucomatous visual field abnormalities in working-age populations,” study limitations were noted, including lack of ophthalmological examinations for all patients and the use of a variety of perimetric methods to analyze results.
In another study using FDT perimetry, carried out at the New England Eye Center in Boston, researchers found that optical coherence topography (OCT) can predict the presence of visual field abnormalities. However, the retrospective study of thickness measurements found that the positive predictive value of optical coherence tomography is likely inadequate for population screening at this time.
Analyzing nerve fiber layer (NFL) measurements in 276 eyes, researchers found that the positive predictive value of OCT was 77% for Swedish interactive threshold algorithm (SITA) perimetry and 72% for FDT perimetry. According to Joel S. Schuman, MD, the value for NFL was significantly higher in patients tested with FDT perimetry than those tested with SITA perimetry.
“These results suggest that either FDT is a more sensitive test or a less specific test than SITA,” Dr. Schuman explained.
Researchers noted that future improvements in imaging technology — higher resolution and better reproducibility — might enhance sensitivity and specificity and increase the chances of OCT for population screening.
Wide field, no mydriasis
The Optomap retinal exam, performed with the Panoramic200 nonmydriatic imaging system, was found helpful in diagnosing retinal disease in a study conducted at the Eye and Ear Institute at the University of Pittsburgh Medical Center.
According to Thomas R. Friberg, MD, the Optomap can be useful in diagnosis of disease without dilation of a patient’s pupil or the benefit of knowing the patient’s clinical history. While Dr. Friberg said that the best way to examine the retina is with indirect ophthalmoscopy, he believes that this device “comes close” to the accuracy of indirect ophthalmoscopy, with the added advantage of a retinal image.
The Optos Panoramic200 is a scanning laser ophthalmoscope that allows large fundus images to be rapidly taken without dilation. The system uses red and green scanning lasers and an optical system with ellipsoidal mirrors to capture a high-quality image.
In Dr. Friberg’s study, 50 random laser ophthalmoscope images of 135 were retrospectively reviewed. The correct diagnosis was made by the first observing specialist 90% of the time. The second investigator made a correct diagnosis 76% of the time.
Encouraging results were also found with the Heidelberg Retinal Tomograph (HRT), which demonstrated high reproducibility in a comparison study conducted in Milan, Italy.
In the study, lead investigator Stefano Miglior, MD, found that the variability of stereometric parameter measurements — induced by the retaking of a series of images to create a mean image with the HRT — was greater than the variability of retracing the contour line of the optic disc.
According to the study, the HRT constructed tomography by using information from a single image acquired at different scan depths.
Comparing the differences among observer-related and image-related sources of variability, researchers found that all expected measurements between the image and observer-related sources were with ±10%, with most falling within ±5%. Standard deviations of the differences between the image evaluations were not statistically significant, and results were “substantial” to “almost perfect” in both observer-related and image-related models.
Retinal thickness analysis
Talia’s Retinal Thickness Analyzer is another option for retinal imaging that can help physicians make treatment and management decisions in glaucoma and retinal disease.
The device uses a series of scans to create a map of the retina in a matter of seconds. Each scan takes only 0.3 seconds. Sequential imaging over time allows surgeons to document the progression or stability of retinal pathology.
Practitioners who have experience with the device note that good quality images can easily be acquired. These can act as substitutes for fluorescein imaging in some situations, without the need for injections and the risk of side effects.
In glaucoma patients, the RTA can document changes in the optic nerve head that may indicate the need for a management change. Recently introduced software allows progressive tracking of the patient from one visit to the next.
According to Edward R. Thomas, MD, who began using the RTA this year, the device’s reproducibility is impressive, as is its versatility.
“The instrument is capable of performing both optic disc and macular analysis, which we feel is extremely important in evaluating patients for glaucoma,” Dr. Thomas said.