Using lasers to image the retina - PMC

Link to weiqing

High quality ophthalmic care depends on the accurate assessment of ocular disease. Conventional direct ophthalmoscopy is used widely and provides good two dimensional views of the retina. However, the true nature of retinal disease is apparent only in three dimensions. In diabetic maculopathy, direct ophthalmoscopy can reveal retinal exudates, but the degree of macula oedema, which usually underlies the decision to treat by laser photocoagulation,1 is less clear. In glaucoma, the earliest damage can be seen as thinning of the retinal nerve fibre layer with increased cupping of the optic disc.2 These changes are best viewed stereoscopically. In both cases, disease of the retinal or optic nerve head will change the surface contour of the retina, either elevating or depressing the retinal surface by up to several hundred micrometres. Clearly, the objective quantification of these changes would be of immense benefit in diagnosing disease and monitoring disease progression and response to treatment.

Summary points

• In diseases such as diabetic maculopathy and glaucoma changes in retinal structure precede visual symptoms

• Earlier detection of these changes allows early intervention and improves the prognosis

• Scanning laser ophthalmoscopes provide rapidly acquired views of the retina that enable the detection of these early changes

• Clinical studies have shown the value of these devices in the diagnosis of glaucoma and diabetic maculopathy

• The costs of these devices is falling and serious consideration should be given to their introduction into hospital based eye services

Diagnosing and monitoring disease

Several studies have examined the ability of these devices to detect glaucoma13&#;15and diabetic macula oedema.16 The tomographic scanning laser ophthalmoscope has been shown to detect glaucoma with high sensitivity (over 80%) and specificity (over 95%).14 These impressive statistics have been achieved without expert ophthalmic assessment and are based on the computerised analysis of retinal structure by the scanning laser ophthalmoscope. These ophthalmoscopes may therefore have a role in detection of glaucoma in primary care.

This technology may also help detect progressive disease in patients who have already had glaucoma or diabetes diagnosed. The ability to detect structural change is an important advantage since these changes usually occur before the onset of clinically detectable visual deficits such as a reduction in visual acuity or loss of visual field. The delay between the structural and visual changes reflects the redundancy of neural components that is built into the visual system. Thus, in glaucoma, it has been estimated that up to 50% of the retinal ganglion cells at any particular location can be lost before a visual field defect is detectable using currently available clinical methods.17 Consequently, if we rely on tests of visual acuity or visual field, significant retinal damage may have already occurred by the time that disease is detected, leading to a poorer visual prognosis.

Early detection also gives clinicians greater flexibility in managing patients. In glaucoma, quantification of the rate of optic disc cupping allows clinicians to estimate the onset of serious visual field loss, which can help when discussing the timing and possible outcomes of treatment. In diabetic maculopathy it may help improve targeting of focal laser treatment. These factors are important since the diseases have mild symptoms in the early stages, and treatment in the form of eye drops, laser, or surgery can have a greater effect on a patient's quality of life than the disease itself.

The other major advantage of these imaging technologies is that they require little patient interaction. This contrasts with commonly used clinical tests such as automated perimetry, which can be arduous for some elderly patients. Furthermore, it is likely that fewer laser images will be needed than visual field tests to detect progression of disease since the noise in a scanning laser ophthalmoscope image is much less than that seen in perimetric tests.18,19 Finally, these devices provide important documentation of the retina and optic disc, which can be valuable when discussing the prognosis or considering the medicolegal aspects of a case.

Implementation of laser technology

The main barrier to the use of scanning laser ophthalmoscopes is that they are expensive. In addition to the initial capital costs, they require experienced staff to operate them and need specialist maintenance. Taking images can, in some cases, be trying for the patient. The eye needs to be relatively immobile while the image is taken and, although the process is rapid for a single image (1.6 seconds for the scanning laser tomograph), three images are usually required to generate a clinically useful topographic map of the retinal surface. Indeed, a recent report of scanning laser ophthalmoscopy in an unselected patient population showed that up to 19% of patients could not provide satisfactory images.20 Patients may also be anxious about the new technology since lasers are often portrayed as powerful agents of destruction; their use as diagnostic tools requires careful explanation.

Further evidence is required to justify the widespread clinical use of scanning laser ophthalmoscopes. Given that the role of the NHS is to deliver a uniform high standard of patient care, the evidence that scanning laser ophthalmoscopes help diagnose diseases such as glaucoma and diabetic maculopathy argues for their installation in most ophthalmic units. However, in many units in the United Kingdom the appearance of the optic disc and macula is still documented by hand, which provides a poor objective record of retinal disease. The introduction of simpler techniques such as stereoscopic optic disc photography, which uses existing fundus cameras, may therefore provide the best value for money since these images have been shown to be of value in distinguishing normal from glaucomatous eyes.21 Similarly, the institution of free eye tests for people aged over 60 is probably a more useful first step than the widespread introduction of scanning laser ophthalmoscopes.22 When so many basic steps have yet to be taken in clinical assessment it may be premature to consider the large scale introduction of such advanced imaging equipment.

Despite these caveats, scanning laser ophthalmoscopy holds great promise for the diagnosis of ophthalmic disease, and it is important that we research its clinical application. In considering the benefits of this technology, we must not conclude that the relentless accrual of data always leads to improvements in patient care. Most patients want to spend as little time in clinic as possible and to receive the minimum necessary investigation and treatment. That said, if detailed topographic images can be acquired rapidly and with minimal discomfort, the wishes of both patient and clinician will be met. The cost of these devices remains a difficult issue. However, as with other electronic devices, this is likely to fall greatly over the next decade as development costs are recouped and computing and electronic costs are reduced. If these developments continue, the widespread use of laser imaging technology in routine clinical practice seems likely.

Footnotes

Funding: Welsh Office of Research and Development

The company is the world’s best Laser Retinal Imaging supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

Competing interests: None declared.

The next time you go for your annual eye checkup, chances are your eye doctor will recommend retinal imaging. This is an additional eye exam that many ophthalmologists are now carrying out. This helps improve the detailed eye exam.

Adding retinal imaging to your eye test may be necessary if you have some conditions. These conditions include diabetes, glaucoma, or age-related macular degeneration. But even if you do not have these eye conditions, retinal imaging can detect severe eye illnesses early and help you protect your vision.

What Is Retinal Imaging?

Retinal imaging or a retinal photograph is a surgery-free and totally safe technique of taking pictures of the back of your eye or retina. The technique allows your eye doctor to have a closer look at your retina, blood vessels, and optic nerve.

There are a few different types of retinal imaging that your eye doctor can use to examine your eye. They include optical coherence tomography (OCT), angiography, and fundus photography. Each of these methods has precise benefits to detecting certain problems in your eye. Your eye doctor will determine the best technique for your specific condition.

How Does Retinal Imaging Work?

Retinal imaging uses low-power lasers to take digital pictures of your retina. The light produced by the lasers goes onto your eye through the pupil. As the light passes through to the retina, it leaves images that are collected by a machine, creating a detailed picture of the retina.

Your eye doctor then looks at these pictures to check what information your retina is revealing about the health of your eye, body, and brain.

Why Is It Important?

Clearer images of the retina make it easier for your ophthalmologist to teach you about your eye health and wellness. You can look at the retinal pictures together and your doctor can identify the different parts of the retina. Then he or she will explain the eye conditions that the pictures reveal and suggest suitable treatment options.

Retinal imaging can reveal the following eye conditions.
 

• Diabetic retinopathy &#; Diabetes can hurt the blood vessels in your retina and cause vision loss if not treated.

• Glaucoma &#; This condition causes a buildup of fluid that can damage your optic nerve and cause irreversible vision loss.

• Age-macular degeneration &#; This illness that comes with age can cause blood or fluid to leak into your retina and make your vision blurry.

• Cancer &#; A dark spot in your retina may indicate a melanoma. Melanoma can grow inside your retina without being detected. If detected early, the melanoma can be treated before it causes severe damage and spread to other parts of the body. 

• Retinal detachment &#; Retinas can withdraw from the wall of your eye and cause permanent loss of vision if not treated properly.

• High blood pressure &#; Symptoms of high blood pressure usually appear first in the retina. Signs can include thinning of the retinal blood vessels, spots, or bleeding in the retina.

For more on how retinal imaging works and why it is important, visit Brandon Eyes at our offices in Middleton or Madison, Wisconsin. You can call (608) 833- or :(608) 833- today to book an appointment.

Are you interested in learning more about Retinal Camera? Contact us today to secure an expert consultation!