Formula comparing rim and disc areas helpful in glaucoma diagnosis

Researchers at the ISIE meeting discussed how advances in technology have led to more precise disease discovery methods.

FT. LAUDERDALE, Fla. — A formula that compares the rim area and disc area of a patient’s two eyes may help differentiate people with glaucoma from those without disease, said a speaker here.

Alvine A. Kamdeu Fansi, MD, and colleagues analyzed four formulas for comparing inter-eye asymmetry of rim area and disc area (IEARADA) designed to differentiate normal and glaucomatous populations. Dr. Fansi spoke about their results here at the International Society for Imaging in the Eye.

“The rim-area-to-disc-area asymmetry may help to distinguish between normal and glaucoma patients,” Dr. Fansi said. “Several formulations of IEARADA exist. In this study, IEARADA 4, a ratio for the ratios, had the most correlations with Heidelberg Retina Tomograph (HRT) II.”

In the study, IEARADA values were calculated based on stereometric HRT values from formulas by Harasymowycz and colleagues (IEARADA-1), Hawker and colleagues (IEARADA-2), and two other formulas. IEARADA-3 was calculated by subtracting the value of smaller rim to disc area from the value of greater rim to disc area. IEARADA-4 is calculated by dividing the two previous values, Dr. Fansi explained.

The 472 participants in the study underwent confocal scanning laser ophthalmoscopy, frequency doubling perimetry technology and a complete exam. In all, 133 had normal results, 105 were glaucoma suspect and 234 had confirmed glaucoma, Dr. Fansi said. IEARADA -4 “seems to be the best asymmetry formula in order to distinguish between normal and glaucoma populations,” Dr. Fansi said. Only 50% of those with glaucoma had IEARADA-4 scores superior to 0.83 compared with 90% of those with normal results.

Study limitations included the reliability and accuracy of HRT II contour line, small sample size of normals and the selection bias between suspect, normal and glaucoma patients, Dr. Fansi said.

More presentations from ISIE are highlighted in the remainder of this article. These items appeared first on the OSN SuperSite as daily reports from this meeting. Look to future issues of Ocular Surgery News for expanded coverage of selected items.

Diagnostic accuracy affected by disease progression

Atypical retardation patterns, such as decreasing typical scan scores, may affect the accuracy of some diagnostic machines, according to one speaker.

Christopher Bowd, PhD, imaged 233 eyes with glaucoma (153 patients) and compared results with 104 healthy eyes of 71 participants. All enrollees underwent GDx Variable Corneal Compensation (VCC) imaging.

“With GDx the macula is scanned to determine the individual, and it gives a properly compensated image for each individual eye,” Dr. Bowd said. “Studies show VCC has better diagnostic accuracy than with fixed corneal compensations.”

The presence of an atypical scan with low typical scan score values decreased the diagnostic accuracy of the VCC, Dr. Bowd said. The diagnostic accuracy “increased with increasing disease severity,” he said.

Dr. Bowd added that recent improvements to the GDx software include enhanced corneal compensation, which have likely successfully addressed the issue of atypical scans.

Reproducibility important in glaucoma imaging

Although there are pros and cons of imaging in different areas of the eye, competitively comparing imaging techniques is not as important as generating an overall picture to assist the clinician in making an accurate diagnosis, said Ran Zeimer, PhD.

Quantitative methods to assess glaucomatous damage vary, and there is a lack of tools to assess the evidence of accuracy. Consistent reproducibility in individual patients is important, Dr. Zeimer said.

“Although it is useful, macular and peripapillary biometry cannot currently be used alone for an unequivocal diagnosis of glaucoma,” Dr. Zeimer said. “Macular and peripapillary biometry, with high reproducibility, promise to be valuable in assessing progression.”

It is still important to meet directly with clinicians to interpret the results of the biometry and measure the function, he said.

“The responsibility is on us and the industry to show that there is relevance between imaging and the function of the patients,” Dr. Zeimer said.

Image quality of great value in glaucoma screening devices

Image quality should be taken into account when assessing discriminatory output of glaucoma imaging devices, said Kyung Rim Sung, MD.

In a study of 164 eyes of 164 patients enrolled in the Advanced Imaging for Glaucoma Study, image qualities were evaluated to compare the discrimination capabilities between healthy and glaucomatous eyes examined with scanning laser polarimetry (GDx VCC), optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy (HRTII).

“Diagnostic accuracy of imaging devices can be affected by many factors,” Dr. Sung said.

Those factors include quality of image, quality of analysis and the individual variance of structure, such as optic disc size, physiological cupping and peripapillary atrophy, she said.

In this study, 102 of the patients were normal, and 62 were confirmed glaucoma patients. All of the patients were scanned with all three of the imaging devices used.

The quality parameters for each scan were quality score for GDx, signal strength for OCT and standard deviation for HRT. The discriminatory parameters were nerve fiber indicator for GDx, nerve fiber layer for OCT and Moorfields regression analysis classification for HRT.

Based on manufacturers’ suggested cut-off criteria for image quality, the GDx had 22.6% poor quality scans; the OCT had 1.2% poor quality scans, and the HRT produced 10.4% poor quality scans, Dr. Sung said.

“To our surprise the results were different among machines,” Dr. Sung said.

Ultrahigh resolution OCT prototype performs unprecedented imaging

The clinical applications of in vivo high-speed ultrahigh resolution optical coherence tomography are invaluable, especially for corneal refractive surgeons, said Viki Christopoulos, MD.

“The clinical applications are especially invaluable for corneal refractive surgeons,” she said. “This is a wonderful technique to evaluate the flap and stroma interface, and it is also important in looking at different complications.”

Dr. Christopoulos presented results on her early clinical experiences with high-speed ultrahigh resolution optical coherence tomography (hsUHR-OCT), a non-contact cross-sectional imaging method to study corneal pathology in vivo.

Compared to other imaging methods, including slit lamp, ultrasound biomicroscopy and confocal microscopy, OCT technology has better resolution, Dr. Christopoulos said.

“Our prototype improved upon this resolution at 3.5 µm and at an incredibly high speed of 24,000 Hz,” she said.

Dr. Christopoulos sampled 12 eyes of six normal subjects who had undergone corneal surgery or trauma to the cornea. The subjects were scanned using the hsUHR-OCT, which takes 4 seconds to scan, and were viewed under a conventional slit lamp.

According to Dr. Christopoulos, the increased scanning rate of this prototype allows 3 × 3 × 1.4 mm and 0.75 × 0.75 × 1.4 mm raster scans of the cornea with 501 × 1024 × 180 samplings in 3.5 seconds.

The magnified images produced in this study were helpful in identifying corneal features that were not seen under conventional biomicroscopy, she said.

The hsUHR-OCT helps to better conceptualize corneal pathology, allows measurements for therapeutic and refractive planning and also helps to better evaluate surgical refractive interfaces and healing to improve surgical outcomes.

HRT II provides useful information for evaluating maculopathy

The retina module of the Heidelberg Retina Tomograph II can provide useful morphological and structural change information for evaluating diabetic and non-diabetic maculopathies, said Robert W. Dunphy, OD.

Dr. Dunphy compared the retina module of the HRT II to other imaging modalities to evaluate macular disorders.

“We know that the HRT II is a confocal scanning laser tomographer that generates retinal surface information when it makes a contact with the retinal surface,” he said.

The retinal module of the HRT II was applied to a sample of patients who had diabetic and non-diabetic maculopathies.

“Findings were correlated with Stratus OCT (Carl Zeiss Meditec) and digital fundus fluorescein angiography in selected cases,” Dr. Dunphy said.

Evaluations of the HRT II scan show topographic and intraretinal features that correlated well with ocular coherence tomography images and fluorescein angiography, Dr. Dunphy said.

For more information:

• The International Society of Imaging in the Eye Meeting was held April 28-29, 2006, in Ft. Lauderdale, Fla.

• Daniele Cruz is an OSN Staff writer who covers all aspects of ophthalmology.