DIAGNOSTICS

Murray Fingeret, O.D.

Screening with Retinal Cameras

Nonmydriatic retinal photography can alert you to signs of ocular disease.

Murray Fingeret, O.D.

A new paradigm is emerging in the practice of Optometry in the use of wide-field retinal imaging as part of the examination routine. Using this technology, you can capture a wide-angle image of the retina, typically through undilated pupils. You can then evaluate the images to look for signs of optic nerve- and retinal disease.

Myriad uses

For some O.D.s, wide-field retinal imaging has become a substitute for the ophthalmoscope. They use it to evaluate the retina and optic nerve exclusively, often without dilating the pupil. Practitioners who run busy commercial practices often use this model with the intention of broadening the examination without having to dilate the patient. The resulting images allow you to view the retinal periphery and are superior to what would have been seen with an undilated view. If you detect an abnormality, you can refer the patient for a consultation, and send the specialist an accompanying copy of the images.

A wide-field image of a patient taken with the Optos Optomap 200.

You can also use wide-field retinal imaging to help you decide which patients require dilation. In this situation, when you recognize an abnormality, a dilated-eye examination is warranted.

A third use for wide-field retinal imaging: screening, with most patients undergoing the imaging procedure at the onset of the exam. In this situation, you use the images to complement the dilated fundus examination, which you still routinely perform. Used as a screening tool, wide-angle retinal imaging alerts you to the potential for a problem that might warrant further investigation.

I believe Optos is responsible for moving the concept of wide-field retinal imaging forward. Still, wide-field retinal imaging has some limitations, such as the low magnification, the extraordinarily wide field and tilted image.

Also, many optometrists do not have one of these devices, but most do have a retina camera. With this in mind, I'd like to propose the use of the digital retinal camera as a screening tool to be used in a similar manner as wide-field retinal imagers.

Benefits of retinal photography

So, what are the benefits of adding retinal photography as a method of screening patients? Until now, screening tests have been limited to intraocular pressure (IOP) measurement and rapid perimetric tests. It's best to conduct screening tests at the beginning of the encounter, so you can use the results to guide the examination. The basic premise for using screening tests is that detecting conditions, such as glaucoma, are not easy. An Australian study found that approximately half of individuals who had glaucoma discovered in a glaucoma screening had received an eye examination in the previous 12 months by either an optometrist or ophthalmologist.¹ So, some cases of glaucoma are missed. This may seem like an extraordinary finding, but if you're familiar with the difficulties of day-to-day practice, you probably don't find this so startling.

Generally, optic nerve head- and IOP evaluation are the signs that will alert you to the presence of glaucoma. However, approximately one-third of individuals with glaucoma never have elevated IOP. Therefore, it's not a very good test in detecting glaucoma, having a sensitivity of approximately 50%.^2,3 Also, if you're not routinely dilating the pupil to evaluate the optic nerve, it's easy to overlook subtle optic nerve changes.

One way you can improve your ability to detect eye disease is through the use of screening tests. For example, optometrists often use Frequency Doubling Technology (FDT) screening perimetry as part of the pre-test battery. If a visual-field defect occurs during the rapid screening exam, you can direct the examination to investigate the reason for the loss. You can use screening retinal photography in a similar way. That is, the photo taken at the beginning of the examination would alert you to an area of concern and the need to direct the examination to evaluate this concern further.

Also, optic nerve/retinal nerve fiber layer signs indicative of disease may be easier to detect with the use of digital retinal photographs when viewed on a computer monitor.

This was recognized in a recent study from the Ocular Hypertension Treatment Study (OHTS) in which 84% of the optic disc hemorrhages were detected upon photographic review and only 16% discovered during the clinical examination (the researchers detected all optic disc hemorrhages found on clinical examination with photography).⁴

Advances in digital retinal photography now allow non-mydriatic, low-illumination images that are remarkable in their image clarity and resolution. The 45° images do not allow the same view of the periphery compared with wide-field retinal imaging, but they still cover the most important retinal areas. If you combine several images, they come close to a 180° view.

In addition, pulling the retinal camera back allows you to take an external photograph that will detect the presence of cataracts and periocular abnormalities.

By educating yourself on the myriad uses and benefits of nonmydriatic wide-angle retinal photography you'll have the ability to effectively employ these devices in your practice to offer patients the best care. OM

1. Wong EY, Keeffe JE, Rait JL, et al. Detection of undiagnosed glaucoma by eye health professionals. Ophthalmology. 2004 Aug; 111(8):1508-14.

2. Sommer A, Tielsch JM, Katz J, et al. Relationship between intraocular pressure and primary open angle glaucoma among white and black Americans. The Baltimore Eye Survey. Arch Ophthalmol. 1991 Aug; 109(8):1090-95.

3. Tielsch JM, Sommer A, Katz J, et al. Racial variations in the prevalence of primary open angle glaucoma. The Baltimore Eye Survey. JAMA. 1991 Jul 17; 266(3):369-374.

4. Budenz DL, Anderson DR, Feuer WJ, et al. Detection and prognostic significance of optic disc hemorrhages during the Ocular Hypertension Treatment Study. Ophthalmol. 2006 Dec;113(12): 2137-43.

5. Cavallerano AA, Cavallerano JD, Katalinic P, et al. A telemedicine program for diabetic retinopathy in a Veterans Affairs Medical Center — the Joslin Vision Network Eye Health Care Model. Am J Ophthalmol. 2005. Apr;139(4):597-604.