Most people will tell you that it’s the sense of sight; as it turns out, research has validated this. In a time trade-off exercise, on average people would choose 4.6 years of perfect health over 10 years without sight. (1) Unfortunately, losing sight is usually not a result of a conscious decision.

Vision is the outcome of a complex system including the eyes, the neural pathway between the eyes and the brain, and the interpretation of neural signals by specific areas of the brain. Visual impairment can result from a deficit or damage to any part of the visual system. (2)

Causes of Vision Loss

In 2020, the global prevalence of blindness was estimated at 43 million. (3) The global leading causes of blindness, from most to least prevalent, are cataracts (15.2 million), glaucoma (3.6 million), undercorrected refractive error (2.3 million), age-related macular degeneration (1.8 million), and diabetic retinopathy (0.9 million). The most common causes of moderate and severe visual impairment are undercorrected refractive error (86.1 million), followed by cataracts (78.8 million), age-related macular degeneration (6.2 million), glaucoma (4.1 million), and diabetic retinopathy (2.9 million). (4)

Some forms of visual loss, such as refractive error and cataracts, are reversible, while others are not. However, many areas of the world still lack access to treatment for these conditions. In the developed world, access to glasses and cataract surgery is more common, making age-related macular degeneration, glaucoma, and diabetic retinopathy important targets for prevention and treatment.

Impact of Vision Loss

The impact of vision loss spans many lives, from those directly affected to their families, friends, and society as a whole. The absence or loss of eyesight can feel frightening and overwhelming, eliciting questions surrounding independence, mobility, mental health, cognition and mortality.

Loss of Independence

Loss of vision has a profound impact on one’s independence. Basic self-care activities become a challenge, including eating, dressing, bathing, and toileting. Instrumental activities of daily living are also impacted, such as driving, shopping, cooking, and financial management. Although both can prove to be challenging, studies have shown that instrumental activities of daily living tend to pose more difficulties than basic self-care. (2) This leads to dependence on other people, whether that be family, friends, or professionals. Older individuals with vision impairment are more likely to need long-term care placement. The Australian Blue Mountains Eye Study found that for each line of visual acuity reduction, there is a 7% increased risk of nursing home placement. (2)

Mobility and Injury

Reduced visual acuity, contrast sensitivity, visual field, and depth perception can pose difficulties in navigating one’s environment. The Low Vision Rehabilitation Outcomes Study found that 16.3% of patients referred to 28 US vision rehabilitation centers reported mobility as one of their top vision concerns. A multitude of studies have shown a relationship between vision impairment and falls. (2) This has the potential for serious injury, including fractures. A study in the United Kingdom studied patients admitted for hip fracture in two hospital districts. They found that 46% of them had visual impairment, most commonly untreated cataract (49%), macular degeneration (21%), and uncorrected refractive error (17%). These patients were less likely to be under the care of an eye care professional and more likely to live in socially deprived areas. (2)

Mental Health

Vision impairment increases the risk of depression, anxiety, and other psychological disorders. Depression and anxiety rates are significantly higher in the visually impaired, as compared to individuals of similar ages suffering from other chronic health conditions such as asthma, chronic bronchitis, heart disease, or hypertension. (2)

Cognition

Cognitive impairment is more common and tends to progress more quickly in the visually impaired. It is unclear whether this is due to a direct or indirect effect of eye disease on cognition. The loss of cognitively stimulating activities, such as reading, in the visually impaired may contribute to the cognitive decline. The brain shows changes in response to diminished visual input, which could impact cognitive processes. The “common cause” theory could also be at play, holding that environmental, genetic, and medical influences impact the eye and the brain simultaneously. It’s also important to consider confounders when looking at the relationship between eyesight and cognition, as factors such as behavior and socioeconomic status could be at play. (2)

Mortality

There appears to be an association between vision impairment and mortality, both injury-related and all-cause. Certainly, visual impairment contributes to accidents and falls. However, there is also an increase in mortality mediated by disability in instrumental activities of daily living. There is also the potential for confounding factors here, including medical conditions, lifestyle, and socio-demographic elements. (2)

The development of tools to measure metabolic abnormalities of the eye may enable diagnosis and treatment before structural change has taken effect.

Quality of Life Metrics

Vision-related quality of life (QoL) is defined as a “complex trait that encompasses vision functioning, symptoms, emotional well-being, social relationships, concerns, and convenience as they are affected by vision”. (5) Vision impairment results in decreased QoL. A US study looked at specific QoL measures among adults aged 40-60 in 22 states. Results indicated that 5.8% of respondents reported life dissatisfaction; 24.8% reported disability; 17.1% reported their health as fair/poor; 12.4% reported 14-30 physically unhealthy days in the past 30 days; 11.0% reported 14-30 mentally unhealthy days; and 18.2% reported 14-30 days of activity limitation. As the level of vision impairment increased, the number of people reporting decreased QoL increased. There is also a positive correlation between reduced QoL and severity of glaucoma, cataracts, age-related macular degeneration, and strabismus. The decrease in QoL between central versus peripheral vision loss appears to be similar. (2)

Healthcare Provider Perceptions

Healthcare providers may perceive the QoL impact of vision loss differently from patients themselves. One study in Canada used time-trade-off tools in surveying medical students on their perceptions of their patient’s vision loss. Medical students had a tendency to underestimate the QoL impact. In China, the impact of glaucoma was studied by comparing utility ratings of patients and ophthalmologists. Ophthalmologists were found to underestimate the impact of mild glaucoma specifically on their patients. (2)

Prevention

Although blindness is certainly a frightening prospect, we can be encouraged by the fact that 90% of vision loss is preventable or treatable. (3) New technologies continue to make advancements in the prevention and treatment of ocular disease. Specifically, the development of tools to measure metabolic abnormalities of the eye may enable diagnosis and treatment before structural change and therefore vision loss has taken effect. These types of advances allow us to hold on to the hope of one day eradicating preventable blindness.

References

1. Enoch J, McDonald L, Jones L, Jones PR, Crabb DP. Evaluating Whether Sight Is the Most Valued Sense. JAMA Ophthalmol. 2019;137(11):1317-1320. doi:10.1001/jamaophthalmol.2019.3537

2. National Academies of Sciences, Engineering, and Medicine. 2016. Making Eye Health a Population Health Imperative: Vision for Tomorrow. Washington, DC: The National Academies Press. doi:10.17226/23471.

3. Burton M, Ramke J, Marques A et al. The Lancet Global Health Commission on Global Eye Health: vision beyond 2020. The Lancet Global Health. 2021;9(4):e489-e551. doi:10.1016/s2214-109x(20)30488-5

4. Steinmetz J, Bourne R, Briant P et al. Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the Right to Sight: an analysis for the Global Burden of Disease Study. The Lancet Global Health. 2021;9(2):e144-e160. doi:10.1016/s2214-109x(20)30489-7

5. Lamoureux E, Pesudovs K. Vision-Specific Quality-of-Life Research: A Need to Improve the Quality. Am J Ophthalmol. 2011;151(2):195-197.e2. doi:10.1016/j.ajo.2010.09.020

Written by the Zilia Team on March 18, 2022