As the science of ocular disease care continues to evolve, the standards and expectations for treatment approaches are likewise raised. Technologies that may have been indispensable a short time ago are now obsolete; relatively new technologies are now indispensable.
In today’s optometric practice, certain technologies and instruments have emerged as crucial components in the detection and management of ocular disease.
Imaging for glaucoma, retinal conditions
Optic nerve imaging has become increasingly important — though not necessarily prevalent — in the detection and management of glaucoma, according to Murray Fingeret, OD, a Primary Care Optometry News Editorial Board member based in St. Albans, N.Y.
“A series of studies reviewing charts from managed care practices showed that only approximately 50% of individuals diagnosed with glaucoma had some form of optic nerve photograph or drawing done at the time of diagnosis,” Dr. Fingeret told PCON. “The percentage of glaucoma patients receiving any form of follow-up documentation declined even further as time increased from the original point of diagnosis.”
Dr. Fingeret emphasized that some sort of image or drawing is necessary to track progression of the disease. “Professional guidelines all recommend this for every newly diagnosed glaucoma patient,” he said. “Without a baseline photograph, it’s difficult to recognize if a person is getting worse. Imaging, whether with the HRT, GDx or Stratus OCT, provides another method for documentation.”
Dr. Fingeret said the Association of International Glaucoma Societies, at its structure-function meeting in 2003, noted that some form of imaging or photography should be performed on every patient classified as having glaucoma or being a glaucoma suspect.
“With imaging, the digital information may be analyzed in sophisticated statistical methods, such as using machine classifiers or neural networks to recognize unusual presentations of the neuroretinal rim, cup depth, cup slope, or retinal nerve fiber layer thickness,” he said.
In addition, Dr. Fingeret said, longitudinal assessment analyzing for change may be done to a greater degree of precision using imaging and its accompanying digital data. “Imaging allows an objective, reproducible method to analyze the optic nerve and retinal nerve fiber layer, which is becoming an important part of the glaucoma workup,” he said.
Among such imaging devices is the GDx (Carl Zeiss Meditec, Dublin, Calif.). According to Joseph Sowka, OD, a professor at Nova Southeastern University in Ft. Lauderdale, Fla., the GDx quantifies nerve fiber layer damage through scanning laser polarimetry.
“This is important because, in the majority of cases, damage occurs to the retinal nerve fiber layer prior to the optic disc or visual field,” he said in an interview.
Dr. Sowka said while focal nerve fiber layer defects are often ophthalmoscopically visible, diffuse atrophy and subtle changes are more difficult to discern. “The GDx VCC not only allows us to identify subtle, early changes to the nerve fiber layer,” he said, “but allows us to compare findings in a patient to other, normal patients of the same age, gender and race through a normative database.”
He said comprehensive examination of the nerve fiber layer can allow practitioners to diagnose glaucomatous damage earlier, often by years, than with conventional perimetry. “If we can diagnose glaucoma earlier, we can begin treatment earlier and we can reduce the amount of vision loss experienced by patients from glaucoma.”
The HRT 3
The Heidelberg Retinal Tomograph 3 (HRT 3, Heidelberg Engineering, Vista, Calif.) is the latest version of the Heidelberg Retinal Tomographer, according to Dr. Fingeret.
The HRT 3 software expands on previous versions and provides information on the cup (cup-to-disc ratio, cup/shape measure), rim (rim area, volume) and retinal nerve fiber layer (RNFL, height variation contour, mean RNFL thickness), Dr. Fingeret said.
“It gives a comparison of inter-eye asymmetry,” he said. “The databases have been expanded to include information for all racial groups, and the TSNIT curve for the RNFL is now color-coded based upon confidence limits.”
In addition, all parameters are marked with symbols regarding the probability of the particular parameter being within or outside normal limits, Dr. Fingeret said.
“A new feature, the glaucoma probability score, is based upon a machine classifier approach to analyze the shape of the retina, optic cup and optic disc as to whether glaucoma may be present.” Dr. Fingeret added that this assessment is not dependent upon the drawing of the contour line.
“The HRT offers a validated approach to recognize change,” he continued. “Differences, if seen, are accompanied by probability values for significance. The HRT also offers a program to analyze the macula for thickness variations, which is important in the management of individuals with diabetic retinopathy.”
The Stratus OCT
The Optical Coherence Tomographer (Stratus OCT, Carl Zeiss Meditec) functions like a B-scan ultrasound, but uses light waves instead of sound waves, providing cross-sectional images of the retina. According to Robert P. Wooldridge, OD, FAAO, a practitioner based in Salt Lake City, Utah, the Stratus is very useful in detecting diabetic retinal edema.
“It is a very sensitive device for detecting thickening of the retina,” he told Primary Care Optometry News, “and it is very specific in determining whether the retina is thickened or elevated with subretinal fluid by giving a cross-section of the retinal layers.”
In a case in which the retina is elevated by subretinal fluid, a primary concern would be a neovascular membrane, as with AMD, Dr. Wooldridge said. Other causes of elevation include central serous retinopathy and pigment epithelial detachment.
“The Stratus OCT is a mainstay of retinal subspecialty care,” he said, “meaning that people who do a lot of retinal care have come to see the value of the OCT in evaluation of the retinal patient, both for diabetic retinopathy and AMD.”
The Stratus OCT also helps practitioners evaluate the effectiveness of their treatment, Dr. Wooldridge said. If a patient has been treated with laser or intravitreal steroidal injection, the OCT can help determine the response to treatment by measuring the change in thickness of the macula.
“It is an objective means of ascertaining response to treatment,” he said.
In terms of early detection with the Stratus, Dr. Wooldridge said that, typically, diabetic retinal edema will cause a drop in central vision if the central fovea is involved. “But you could have perifoveal edema with fairly good central vision, and it may not be obvious on clinical evaluation,” he said. “In these cases, the Stratus may help with early detection.”
He said the Stratus also helps differentiate atrophic macular damage secondary to diabetic ischemia vs. true macular edema. “If the retina is edematous and not atrophic, treatment may be indicated and helpful,” he said.
The RTA (Talia Technologies, Holiday, Fla.) functions as a combined digital fundus camera, computerized scanning slit lamp and retinal thickness analyzer. The instrument allows for the acquisition, display and analysis of retinal optical cross-sections and provides registered maps of retinal thickness and comparative reports.
“To me, the most valuable thing about the RTA is its ability to look at the retina for pathology as well as the optic nerve,” said Eric E. Schmidt, OD, a practitioner at Bladen Eye Center in Elizabethtown, N.C. “The general optometrist will see as many patients with diabetes or AMD as with glaucoma. So having an instrument that images both the retina and the optic nerve – and gives you real-time data – is invaluable. It opens up a whole other diagnostic area.”
Dr. Schmidt told Primary Care Optometry News that the practitioner can direct the instrument to image the optic nerve head topographically in order to follow the optic nerve over time very well. “For glaucoma, it is very important to be able to react to changes over time,” he said.
In addition, the RTA can also image the nerve fiber layer and the macular region, which is the original source of the pathology of glaucoma. “This is good for early detection. It’s not computer-interpolated data,” he said. “It’s real data based on real-time thickness data. You also have a live picture of the slit data, so you can see where the numbers are bearing out.”
Pachymetry and topography
The use of pachymetry in refractive surgery is “beyond important,” according to Paul M. Karpecki, OD, FAAO, a Primary Care Optometry News Editorial Board member practicing in Kansas City, Mo.
“It’s essential; it’s required standard of care,” he told PCON. “Pachymetry tells you a lot about the risk of ectasia. You want to stay within the neighborhood of 300 microns of tissue available in the bed, and the only way to do this is by measuring pachymetry preoperatively.”
“You can assess this by measuring pachymetry in the center and then mid-peripherally at 5, 6 and 7 o’clock,” he said. “A normal cornea thickens as you move peripherally, so if it doesn’t, that’s a red flag.”
In addition, pachymetry detects guttata, which may be an indicator of conditions such as Fuch’s dystrophy, Dr. Karpecki said. “You confirm the presence by a very thick cornea,” he said, “because if it is swollen, it thickens, and that is what Fuch’s dystrophy is. That is another situation where you would not pursue LASIK.
Topography is also a necessary tool in refractive surgery and is especially essential to the surgeon’s armamentarium, Dr. Karpecki said.
“It is below standard of care for a surgeon to not at least have an Orbscan [Bausch & Lomb, Rochester, N.Y.],” he said. “Within the last 12 to 18 months, there have been more than $20 million in lost lawsuits over ectasia. If those surgeons had used an Orbscan, these lawsuits may have been prevented.”
For the optometrist, topography is helpful but not essential, Dr. Karpecki said.
“For the OD, the Orbscan can confirm or not confirm keratoconus and pellucid marginal degeneration and rule out those candidates for LASIK,” he said. “Topography combined with pachymetry may prompt an optometrist to recommend PRK or other more suitable treatment options.”
Pachymetry is also useful in gauging the risk of keratoconus, Dr. Karpecki added.
The Panoramic 200
Optos’ Panoramic 200 (P200, Optos North America, Marlborough, Mass.) is a wide-field imager (200°) that captures a fundus image in one-quarter of a second.
According to William Jones, OD, FAAO, a Primary Care Optometry News Editorial Board member based in Albuquerque, N.M., the P200 is able to find most peripheral retinal problems. “The end of the retina is 240° out, and, therefore, it may miss something in the far periphery,” he said. “A view farther out in the periphery can be achieved by eye steering.”
However, Dr. Jones added that many eye doctors can miss problems in the far periphery with standard types of ophthalmoscopes. “There is no perfect instrument,” he said. “The best way to examine the fundus is to use both methods. Also, if a lesion is detected with the P200, then the clinician can search the involved area immediately with ‘targeted ophthalmoscopy.’”
It is this combined use of instrumentation, he said, that enables clinicians to acquire the most fundus detail.
Dr. Jones said the P200 is best at detecting retinoschisis, retinal detachments, retinal hemorrhages, retinal/choroidal tumors, peripheral vascular abnormalities, vitreous hemorrhage, peripheral drusen and choroidal nevi.
“However, other lesions can be detected, such as significant cataracts, Scheie’s lines in pigment dispersion syndrome, asteroid hyalosis, significant floaters and IOL opacification,” he said.
The PreView PHP
The Preferential Hyperacuity Perimeter (PreView PHP, Carl Zeiss Meditec) was designed to detect age-related macular degeneration from the intermediate stage to neovascular.
According to Neil M. Bressler, MD, principal investigator of a study conducted on the PHP at Wilmer Eye Institute, Johns Hopkins University, the device has the ability to detect visual functional changes while handling problems intrinsic to the Amsler grid, including loss of fixation and cortical completion.
In an article discussing the findings of this study (Ophthalmology, 2005;112:1758-1765), Dr. Bressler said the PHP can detect choroidal neovascularization (CNV) among a population with recent-onset CNV from AMD or the intermediate stage of AMD “with a high sensitivity, specificity, positive predictive value and accuracy.”
Dr. Bressler said most cases of CNV detected either did not extend beneath the center of the macula or were a subfoveal lesion with qualities that were shown to have the best post-treatment outcomes.
“The findings from this study suggest that periodic monitoring with the PHP is likely to detect recent-onset CNV for which treatment would be indicated,” he said in the article. “Furthermore, treatment of recent-onset neovascular lesions similar to those detected in this study often would have a relatively good outcome, because the CNV detected in this study usually was small or not subfoveal, compared with had it grown quite large, had it been associated with fairly poor visual acuity or both.”
For Your Information:
- Murray Fingeret, OD, can be reached at Linden Blvd and 179th St., St. Albans, NY 11425; (718) 526-1000 ext. 2435; e-mail: email@example.com. Dr. Fingeret has no direct financial interest in the products he mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Joseph Sowka, OD, can be reached at Nova Southeastern University, 3200 South University Dr., Ft. Lauderdale, FL 33328; (954) 262-1472; e-mail: firstname.lastname@example.org. Dr. Sowka is a paid consultant for Carl Zeiss Meditec.
- Robert P. Wooldridge, OD, FAAO, can be reached at the Eye Foundation of Utah, 201 E 5900 South, Ste. 201, Salt Lake City, UT 84107; (801) 268-6408; e-mail: email@example.com. Dr. Wooldridge has no direct financial interest in the products he mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Eric E. Schmidt, OD, can be reached at 409 E. Broad St., Elizabethtown, NC 28337-8807; (910) 862-4268; e-mail: firstname.lastname@example.org. Dr. Schmidt has no direct financial interest in the products he mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Paul M. Karpecki, OD, FAAO, can be reached at 5844 NW Barry Road, Ste. 200, Kansas City, MO 64154; (816) 746-9800; e-mail: PaulK-VC@kc.rr.com. Dr. Karpecki is a paid consultant for Bausch & Lomb.
- William Jones, OD, FAAO, can be reached at 1828 Conestoga, SE, Albuquerque, NM 87123; (505) 293-7347; e-mail: email@example.com. Dr. Jones is a paid consultant for Optos and has a direct financial interest in their products.
- Neil M. Bressler, MD, can be reached at 550 N Broadway, Ste. 115, Baltimore, MD 21205; (410) 955-3518; fax: (410) 955-3518; e-mail: firstname.lastname@example.org.