Testing: Embrace new technology to examine internal structures

October 1, 2009

Visual field instruments have changed in their abilities to detect fundus abnormalities.

Those instruments were the best that we had at the time. By using one or two of them, a good view of the internal structures was accomplished. We were very sure that we could see almost anything in the fundus.

However, modern technology has proven to me over and over again that my eyes were not as good as I once thought they were.

Scanning laser ophthalmoscopes (SLOs) and fundus imagers give us new ways to view the fundus, both in the extent of the viewing area and details not seen as well with white light instruments. One type of SLO is able to obtain a very wide field that can be used with either dilation or without dilation. SLOs in development and research give some of the finest detail of the scanned tissues. Modern fundus cameras can montage a number of images into a wide field image that is almost seamless. These wide-field images allow for a better understanding of the size and location of fundus lesions and have increased our knowledge of peripheral lesions.

Even though the Hruby and 90-D lens have been in existence for years, there are newer lenses that I have found to be more useful. The wide-field lenses allow for a much greater viewing area of the fundus. This allows for a view of the periphery with the slit lamp and lens that rivals the BIO. The advantage of the BIO is a wide-field view of the fundus area but low magnification and stereopsis and the pre-corneal lens allows for a smaller area of view with higher magnification and greater stereopsis. Thus, a peripheral retinal examination can be achieved with the slit lamp and one of these lenses.

Detecting defects

Visual field instruments have changed in their abilities to detect fundus abnormalities. Bowl perimeters can detect fundus lesions of significant size, such as retinal detachment or large tumors, by plotting out scotomas. The Amsler grid is able to detect small defects in the visual field by detecting distortions in the central field. Today, there is an instrument that can detect when dry age-related macular degeneration (AMD) converts to the wet form by using Vernier acuity on flash presentations. There is a sophisticated algorithm with the computer system to determine this change in the visual field. It is far more sensitive than the Amsler grid. I have seen conversion in a number of my patients.

Currently, an instrument is in development that employs a moving grid pattern to detect the presence of abnormalities from pre-retinal to the visual cortex. It appears to be highly sensitive in its ability to detect numerous abnormalities. So far, in my hands, it has detected fresh and residual migraine distortions, cerebral stroke and mass lesions, glaucomatous field defects, AMD, diabetic retinopathy, central serous retinopathy, and more. This is exciting technology because it finds numerous types of lesions along the entire visual pathway.

OCT technology

Ocular coherence tomography (OCT) provides a cross-sectional view of tissue and has the ability to determine height and thickness of scanned tissue. The original instrument was based in time-domain, but new versions are based in spectral- or Fourier-domain. Either form works well, but spectral-domain has greater resolution and a much faster capture time. Viewing the ocular tissues allows for an image of lesions and situations not appreciated to such an extent with the human eye.

The vitreoretinal interface actually can be seen in excellent clarity and vitreous traction of the smallest magnitude can be appreciated. What we have learned by studying the vitreoretinal interface has advanced greatly our knowledge of vitreomacular (foveal) traction, macular hole formation, epiretinal membrane formation, etc. In my professional opinion, if you are interested in examining the retina or seeing retinal patients, you must have some form of OCT instrumentation in your office.

It is an exciting time to be involved with intraocular testing and evaluation. We can see and learn about retinal and visual pathway diseases like never before. In the short and long of it, modern instrumentation is making us all smarter and more competent in diagnosing and treating our patients.

William L. Jones, OD, is in private practice in Albuquerque, NM, focusing on primarily retina and glaucoma matters. Dr. Jones is a consultant for Carl Zeiss Meditec, Notal Vision, Optos, Rush Ophthalmics, and Volk Optical. Readers may contact Dr. Jones via e-mail at wjones556654@comcast.net