As the aging process gradually transforms our bodies, changes in vision are a natural evolution. Since we enter the era of most dramatic eye degeneration around the same time as HD onset, it is important to understand how vision naturally changes and how that may add to the challenges Huntington’s presents.
In parallel to the average age of HD onset, one of the most common processes affecting vision, called presbyopia, develops around age 40. Presbyopia is the gradual hardening of the eye lens, which causes difficulty in focusing on small objects or close items. Presbyopia is typically treated with reading glasses, bi-focals or transitional lenses. As hardening continues with time, so too prescriptions may need repeated adjustment from year to year.
Other frequently developing conditions include decreased color vision, dry eyes, and tearing (having too many tears). Peripheral vision loss also begins, at a rate of about one to three degrees per decade of life. By 70 to 80 years of age, there can be a decrease of 20 to 30 degrees of peripheral vision. Additionally, the muscles controlling pupil size loses strength, reducing the eyes’ responsiveness to light. Because of this, adults in their 60’s require three times more ambient lighting to read comfortably than those in their 20’s.
After age 50, the risk of eye diseases increase, particularly for glaucoma, macular degeneration, and cataracts.
While technically classified as an age related disease, cataracts are so common some consider them a natural part of aging. Cataracts cause blurred or hazy vision and can exist as small easily ignored areas, or cover the entire eye. Cataracts disrupt contrast sensitivity, which is the ability to discern between bright and dim elements in a static image. Research from Indiana University indicates that symptomatic HD patients also show a decline in this sensitivity. Surgery is the typical treatment for cataracts, and usually restores the vision lost or hampered by the cataracts. However, if the decline in contrast sensitivity is due to HD progression, daily adjustments to create a higher contrast environment can help.
Unlike the hazy look cataracts cause, macular degeneration (AMD) manifests in distorted vision and a dimming or loss of central vision. Macular degeneration is incurable and the leading cause of blindness among American seniors. However, treatments to slow the disease include quitting smoking, eating leafy greens, and taking an AREDs supplement.
Risk for glaucoma increases each decade after age 40, from around 1% up to 12% by age 80. While there is still research ongoing determining the cause, intra-ocular pressure plays an important role. Glaucoma can develop over time, or it can be brought on by eye infections, blocked blood vessels inside the eye, or injury to the eye. In most cases, there are no identifying symptoms until the optic nerve has been damaged. It is for this reason that regular eye exams are crucial for early detection.
HD patients often develop ocular motor apraxia (OMA), a condition where purposeful horizontal and quick eye movement becomes impaired. There are several elements to this apraxia, including delayed initiation of movement, fixation impairment, and inability to follow an object without moving the head. Unlike those that develop OMA due to hemorrage or tumor, OMA in HD patients does not seem to effect the vestibular-ocular reflex. This is the reflex which causes the eye to move in the opposite direction of head movement to maintain image stability.
Like so many elements of Huntington’s, there is no solution to resolve the issue of OMA; however, healthy lifestyle choices such as abstaining from smoking and attention to diet can help reduce the severity of many of these conditions. For some diseases of the eye early detection and condition management is the only path. Understanding how these various impairments present themselves is therefore important not only for ourselves, but for the ones that we look after.
Disclaimer: I am not a doctor. All information in this article is purely for educational and enrichment purposes and is not intended to replace or provide medical advice.