Diagnosing Eye Disease

Because many eye diseases can lead to severe and irreversible vision loss, it is essential that individuals in the early stages of disease be diagnosed as soon as possible. In many cases, vision loss associated with glaucoma, diabetic retinopathy and age-related macular degeneration may be avoided by addressing risk factors associated with these conditions.

Researchers at the Donald K Johnson Eye Institute have discovered many early changes in the eye that can be used to diagnose disease and are an active part of creating better testing processes. For example, Dr. Chris Hudson and his colleagues were the first to report specific changes in the flow of blood within the retina that can be early indicators of diabetic retinopathy – and they continue to study new screening tests for retinal disease. Similarly, Dr. Agnes Wong is currently leading a trial which aims to identify the best approach to screening for vision problems in school age children. This trial will help develop standards for vision care in Ontario.

Learn more about the work happening at the Donald K Johnson Eye Institute to develop new diagnostic tools for eye diseases:

Clinicians at the Donald K Johnson Eye Institute are partners in testing new diagnostic tools. Their input helps ensure that new measures can be implemented and provide practical information for regular practice.

Measuring Ocular Blood Flow

The retina at the back of the eye relies on a network of tiny blood vessels to supply nutrients and oxygen. Damage to these blood vessels is a feature of many major eye diseases including diabetic retinopathy and age-related macular degeneration. Researchers at the Donald K Johnson Eye Institute are studying ways to monitor the health of these blood vessels. Technology which could detect problems in blood flow and regulation early could be used to screen people with diabetes, and prevent vision loss before it occurs.

Researchers Christopher Hudson and John Flanagan have helped to develop sophisticated equipment that is now used to test ocular blood flow in ophthalmology clinics. One example is the retina screening component of the Heidelberg Retina Tomograph 3.  Dr. Hudson continues to work with other commercial interests to develop specialized equipment for clinical testing of eye disease.

Photo: Precise measures of ocular blood flow make early diagnosis and treatment possible. (Photo Credit: National Eye Institute, National Institutes of Health.

Dr. Hudson also conducts detailed studies of blood flow in the retina to look for tiny changes that may be early warning signs of vision loss. For example, with each beat of the heart, the speed (velocity) of blood flow throughout the body ebbs and flows (pulses). This can be measured as a ratio of maximum blood flow speed to minimum blood flow speed. Dr. Hudson’s team has shown that a high maximum:minimum velocity ratio is an early warning sign of blood vessel damage.

Dr. Hudson’s research in this area is supported by a grant from the Ontario Research Fund for Research Excellence and through partnerships with commercial partners.

 

Vision Screening for Pre-school Children

Agnes Wong of the Donald K Johnson Eye Institute is also a Senior Scientist and Ophthalmologist-in-Chief at the Hospital for Sick Children. Through the Hospital for Sick Children, she is operating a large trial across Ontario which aims to improve vision screening for pre-school children. This research is being conducted in partnership with Dr. Daphne Maurer at McMaster University.

This trial aims to identify efficient and cost-effective ways to screen young children for vision problems. Each year, it is estimated that 5000 children in Ontario lose sight in one eye because eye problems are not diagnosed promptly, and 10,000 have difficulty learning to read because their eye problems are not being detected. This trial aims to diagnose common vision problems of early childhood including refractive error (near-sightedness or far-sightedness, amblyopia (lazy eye) and strabismus (misaligned visual axes).

Photo: Dr. Wong is leading a large Ontario trial screening school children for vision problems. (Photo credit: National Eye Institute, National Institutes of Health)

The trial will offer the following vision tests at schools to children ages 3-5 in junior or senior kindergarten:

  • A letter eye chart called the Cambridge Crowding Cards (adapted for pre-schoolers)
  • tests for stereoscopic vision (how well the eyes work together)
  • Two different devices to test for refractive error
  • A machine that measures the alignment of the eyes

Follow-up visits with an optometrist, and the prescribing of glasses if necessary, will also occur at the school at a time when one of the child’s parents can attend.

To learn more about this trial, visit http://www.visionscreening.ca/

This research is supported by grants from the Canadian Institutes of Health Research and the National Science and Engineering Research Council of Canada.

Chromatic Pupillometry

Briefly flashing a bright light in a person’s eye(s) and watching for changes in the pupil diameter has long been used as a rapid means to assess damage to the brain and visual system. However, recent technological refinements have expanded the scientific and clinical diagnostic utility of pupillometry.

Photo: Pupillmetry uses flashes of light to diagnose damage to the eye.

Studies of the light-sensing photoreceptors of the eye have begun to explain this response. The retina has long been known to have two types of photoreceptors: cone photoreceptors responsible for detailed central vision, and rod photoreceptors responsible for peripheral and dim light vision and motion detection. A recent study has revealed a third type of photoreceptor: intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells respond preferentially to bright blue light, driving a constricting response of the pupils that can persist for many seconds after the light is extinguished.

This new class of light-sensing cells provides an opportunity for a new diagnostic tool to measure both vision damage and brain damage. Precise measurement of changes in pupil constriction in response to carefully-controlled colored light can help localize specific areas of damage within the eye and the optic nerve associated with retinal disease or glaucoma, and also help localize injuries to the brain, or even help assess cranial nerve damage and migraine. To date all of these applications remain experimental.

Dr. Agnes Wong, a researcher at the Donald K Johnson Eye Institute, has been adapting the methods used in chromatic pupillometry to improve their diagnostic utility. Often precise measures can be difficult to obtain because sustained bright light can cause participants to blink during testing. Dr. Wong and her team are testing ways of exposing different regions of the eye to light as well as working to shorten the period of light exposure without compromising the testing.

This research is supported by a grant from the Canada Foundation for Innovation.

Visual Fixation Measurements

In people with normal vision, the gaze is fixated on the fovea, since this area of the retina provides the highest quality vision. However, in people where the central vision has been damaged by age-related macular degeneration, macular holes or other conditions damaging to the macula, the eye naturally tries to use other areas of the retina that are less damaged. Retraining techniques can aid this process. Tests which determine where this new fixation point has been established, and that evaluate the stability of that fixation, are becoming useful tools for monitoring treatment success and guiding rehabilitation.

Donald K Johnson Eye Institute Scientist Martin Steinbach has studied fixation and fixation stability in a number of conditions. He and his team (Research Associates Esther Gonzalez and Lumi Tarita-Nistor) have also looked at how surgical treatment of macular holes and how drug treatment of wet age-related macular degeneration, affect these measures. His work is providing important information about the course of recovery in these conditions, and where more rehabilitation efforts may be needed. This testing may also provide useful measures of visual rehabilitation helping evaluate treatments for macular disease.

Photo: Dr. Steinbach and staff measure a person’s preferred retinal locus.

Diagnose Neurodegenerative Disease through Ocular Testing

The eye is a potential window to the brain, the only place in the body where clinicians can examine nervous tissue without invasive tests. Thus, scientists at the Donald K Johnson Eye Institute are beginning to evaluate using diagnostic tools that examine the eye to provide early warning of neurodegenerative disorders like Alzheimer’s Disease and Parkinson’s Disease, and to help with ongoing monitoring of these conditions.

Donald K Johnson Eye Institute scientist Chris Hudson works with other investigators from across Ontario as part of the Ontario Neurodegenerative Disease Research Initiative (ONDRI). His research uses Spectral Domain Optical Coherence Tomography to examine the thickness of the various strata / layers of the retina. This equipment is now frequently available in optometrist’s offices where it is used to provide early warning of diseases like glaucoma and age-related macular degeneration. However, it can also be used to look for more subtle changes in retinal thickness in people with early Parkinson’s Disease and Alzheimer’s Disease. If Dr. Hudson’s research proves that this is the case, this test could become a widely-used and easily accessible screening tool for neurodegenerative disorders. Learn more about this screening tool. The Ontario Neurodegenerative Disease Research Initiative is funded by a grant from Brain Canada.

Donald K Johnson Eye Institute adjunct scientist Moshe Eizenman also studies the eye to detect and monitor disease. His team develops methods and systems to measure eye movements and visual scanning patterns. These measures can be used as objective physiological markers for cognitive biases in information processing of patients. His team is developing methods to detect biases in information processing in patients with post concussion syndrome, eating disorders, mood disorders and Alzheimer's disease. Such testing can provide an objective measure of disease progression and might be used to evaluate treatments. Learn more about this research.

Photo: Monitoring eye movements can help diagnose and assess neurodegenerative disease.