Functional Vision Loss

According to the World Health Organization, 2.2 billion people worldwide have a visual impairment. William Smith, DO, Assistant Professor of Ophthalmology at the University of Pittsburgh School of Medicine, projects that all these individuals have some level of functional vision loss. The prevalence is expected to double over the next 30 years due to an aging population.

Definition of Functional Vision Loss

What is functional vision loss, anyway? Functional vision is how the individual is utilizing their vision as related to real-world activities. Functional vision is separate from visual function, which is what is measured and tested during an eye exam. Functional vision loss can be defined as having any eye condition that affects a person’s ability to perform daily living tasks. Caused by any degree of visual impairment, it can be the result of conditions like age related macular degeneration, glaucoma, diabetic retinopathy, stroke, retinitis pigmentosa, and genetic retinal dystrophies.

All age ranges experience functional vision loss, but it is more common in the elderly because risk increases with age.

Diagnosis and Evaluation

Based upon their vision, patients are asked about their limitations. Current treatments include a comprehensive low vision evaluation and low vision rehabilitation. During these appointments, visual performance is assessed and compared to the patient’s visual needs and goals. Optical devices, electronic devices, technology, non-optical devices, and compensatory strategies are evaluated and recommended to address the patient’s visual needs.

This is a multi-disciplinary team approach with a residency trained low vision optometrist like Dr. Smith and a specialty trained and certified occupational therapist like Holly Stants, MS, OTR/L, SCLV, CLVT, who serves as the UPMC CRS Low Vision Rehab Team Leader. Teachers of the visually impaired and orientation and mobility instructors may also be enlisted to help.

Vision Rehabilitation

The American Academy of Ophthalmology recommended in 2016 that vision rehabilitation become part of the standard of care for patients with vision impairment. Once Stants gets a referral from a medical professional, she begins the evaluation process, which is as follows:

  • Review medical history
  • Ask how vision impacts daily activities
  • Ask what is most important (for Patient Specific Functional Scale) so intervention can be tailored to patient’s goals
  • Screen reading ability
  • Screen ability to see contrast
  • Screen how eyes work together
  • Check ability to adapt to lighting and glare
  • Complete lighting assessment to promote ability to use best lighting at home
  • Review many strategies to assist with functional vision
  • Provide education on use of contrast and lighting in environment to promote efficiency, ease of access, and safety/fall prevention
  • Review technology and what patient can do with the technology they have
  • Introduce technology patient might not know about or have at home
  • Provide information on community resources and how to get additional assistance for funding of equipment

Dr. Smith’s number one recommendation is for individuals to communicate with their eye care professionals that they are having difficulty functioning related to their vision loss. This, in turn, can lead to earlier referrals to low vision to begin addressing and ultimately improving their functional performance.

Low Vision Challenges

Vision comes from the brain, which makes vision loss complicated. Each person experiences it differently, so even if two people have the same diagnosis, they may see very differently. Up to 70 percent of the brain is organized to process vision, which is why it is important to always get checked out with a head injury regardless of severity, Stants said. In fact, depending on the type of vision loss, sometimes there is a delay in processing when the person must take time to understand or look at what they are seeing.

Sometimes, a person may experience something called phantom vision or Charles Bonnet Syndrome, when they see something that is not there. “This does really happen,” said Stants, “and a person should be aware that it can happen and that it does not mean that they are losing their mind. Rather, the brain tries to fill in where it is missing something and just like when a person loses a limb and may think their foot is still there, the vision system provides images because the vision is missing.”

Perceptual completion is another phenomenon where the brain tries to complete something (e.g. with the word “bread,” they may miss “r” and say, “it is really bead”). This may happen during reading tasks. Sometimes a person may lose side vision but still be quite capable of using their vision for reading.

Different Kinds of Vision Loss

There are many kinds of vision loss, including:

  • Central field loss: Difficulty seeing details (including reading), contrast, color (including faces), driving, may experience missing words or parts of words
  • Peripheral field loss/side vision: Difficulty to navigate/walk, especially in a new, fast paced environment. May result in bumping into things, preferring to stay home due to fear of travel, frequent falls, increased challenges in low lighting, often walk while staring at feet.
  • Loss of visual field (quarter, half): Also referred to as quadrantonopsia or hemianopsia. May happen with stroke, brain injury, or cancer. Can be complicated learning to turn head.
  • Mixed: Combination of vision loss that can be complex. There are still ways to manage with strategies.

Whatever the loss, the most important part of Stants’ job is to help patients identify how their vision loss impacts their daily living activities and how they can use their remaining vision to promote their independence.

The Future of Functional Vision Loss

The good news is there are more treatments and related developments on the horizon if not already in existence. Vision restoration, for example, has promise thanks to optogenetics (GenSight) and Pixium retinal prosthesis. Emerging technologies like eSight glasses and apps for smartphones and tablets will make it easier for functional vision loss.

As the UPMC CRS Low Vision Rehab Team Leader and clinical interventionist, Stants is working with current studies involving vision restoration technologies to improve visual performance/functional vision in patients with end stage age related macular degeneration and retinitis pigmentosa. She is also looking at the functional impact of the Iris Vision electronic digital head bourne magnification system with patients who have moderate to profound central vision loss. Stants is part of a research center exploring wireless technologies for people with disabilities and will be working with Pitt’s adaptive driving program on bi-optic driving.

Advice for Patients

At UPMC Eye Centers, patients are in good hands. “I see the person, not the vision,” Stants said. “I am happy to facilitate new opportunities and hope for living with a chronic disease that causes barriers in life.”

Stants encourages patients not to lose hope, as there is always something that can be done. “Keep informed, learn about new ways to do things, be open about what you can do to improve your current life and use of your current vision,” she said. “We are here to help you.”