10.7 Visual Neuroscience and Visual Deficiencies

Visual Neuroscience and Visual Deficiencies

Learning Objectives

  • 10.7.1: Describe how improper focusing of images on the retina causes myopia.

  • 10.7.2: Discuss theories of why myopia is more common than it used to be.

  • 10.7.3: Describe amblyopia and how it is treated.

  • 10.7.4: Describe macular degeneration and ways it might be treated in the future.

Importance of Vision

  • Humans are a vision-oriented species, emphasizing efforts to:

    • Prevent impairment of vision

    • Improve inadequate vision

    • Restore sight to the blind

  • Current Statistics:

    • In the United States, 500,000 people are blind.

  • Impact of Medical Advances:

    • Some causes of blindness are reduced due to medical advancements.

    • However, new causes of blindness have arisen, notably from diabetes, for which blindness prevention remains difficult.

Prevention and Improvement of Vision Impairments

  • Myopia (Nearsightedness):

    • Defined as a condition where distant objects appear blurred due to images focusing in front of the retina.

    • Cause: Eyeball is too long.

    • Greek derivation: From "myein" (to be closed) and "ops" (eye).

    • Studies show that incidence of myopia can be reduced, especially in children and nonhuman animals.

Theories on Increasing Myopia Rates

  • Environmental Factors: Certain factors exacerbate excessive eyeball growth.

  • Previous Beliefs:

    • Modern habits of close object focus (reading, computer screens) believed to cause myopia.

  • Current Understanding:

    • Indoor lighting poses potential risk for myopia development.

  • Lifestyle Changes Before/After Civilization:

    • Increase in time spent indoors under artificial lighting (which differs in brightness and composition from sunlight).

    • Children with myopia spend less time outdoors, influencing the correlation with genetics.

Studies and Evidence

  • Comparative Study:

    • Chinese children in Singapore (30 mins outdoors) showed 30% myopia, while those in Sydney (2 hours outdoors) showed only 3% myopia. (Rose et al., 2008).

  • Effect of School Recess:

    • Outdoor recess time of 80 minutes leads to reduced incidence of myopia (Wu et al., 2013).

  • Impact of COVID-19 Pandemic:

    • Second graders experienced greater eyeball elongation during lockdown due to decreased outdoor time (Hu et al., 2021).

Amblyopia

  • Condition: Amblyopia is characterized by poor visual acuity in one eye despite normal function of the eye and retina.

    • Origin: Greek roots "amblys" (dull) and "ops" (eye).

  • Causes: Misalignment of eyes leads to suppression of visual information from one eye.

  • Treatment Options:

    1. Surgical Correction: Adjusting eye muscle balance.

    2. Practice and Training: Includes patching the dominant (strong) eye to encourage use of the weak eye.

  • Results from Intervention Studies:

    • A study with 507 patients showed that 50% improvement in amblyopia occurred in patients who wore eyeglasses and patches versus 25% in those who only wore eyeglasses (Pediatric Eye Disease Investigator Group, 2005).

Case Studies and Observations

  • Observations from individuals (e.g., Michael May, who regained partial vision post-blindness) indicate potential for recovery through targeted visual training.

Macular Degeneration

  • Definition: Visual impairment resulting from damage to the retina's photoreceptors.

  • Types:

    • Dry Macular Degeneration: Causes atrophy of the retinal pigmented epithelium, leading to photoreceptor death.

    • Wet Macular Degeneration: Characterized by abnormal retinal capillary growth causing retinal detachment or further photoreceptor death.

  • Impact: Primarily affects the fovea, resulting in significant visual impairment.

  • Current Management Strategies:

    • The Age-Related Eye Disease Study (AREDS) found that antioxidants and vitamins can slightly slow disease progression (Evans and Lawrenson, 2017).

Research on Restoration Techniques

  • Photoreceptor Transplantation:

    • Research focuses on maximizing integration of transplanted rods to restore vision in individuals with photoreceptor loss.

    • Example Study: Mice with genetically disabled rod photoreceptors received healthy rod cells, effectively restoring vision (Pearson et al., 2012).

  • Functional Testing:

    • Studies involved monitoring mouse responses to moving visual stimuli to ensure regained vision capabilities.

  • Future Directions:

    • Exploration of human stem cell-derived photoreceptors for potential transplantation as a vision restoration strategy (Yao et al., 2018).

Novel Approaches to Vision Restoration

  • Use of Viruses:

    • Techniques that induce retinal cells to respond to light through gene editing (e.g., channelrhodopsin) provide potential frameworks for future therapies (Doroudchi et al., 2011).

Conclusion

  • Continued research and intervention strategies promise advancements in the prevention and treatment of visual impairments such as myopia, amblyopia, and macular degeneration.

Ethical Implications and Future Considerations

  • Ongoing exploration into the balance of sunlight exposure and indoor lighting effects on children's visual health.

  • Ethical considerations associated with photoreceptor sourcing for transplantation in humans.