Impaired vision and blindness: possible conditions as causes

Which eye conditions cause impaired vision and blindness?

The following eye conditions account for most cases of impaired vision in the general population: a refraction error, macular degeneration, diabetic retinopathy, glaucoma and cataract. Prevalence rates increase with age.

In a random sample of 1598 people with intellectual disabilities with an average age of 45.7 years, the following eye conditions were found to be responsible for most cases of visual impairment  ¹⁹⁴ : refraction disorders, strabismus, cataract, glaucoma, keratoconus, corneal cloudiness and microcorneae. In addition, there are also age-related causes of visual impairment: macular degeneration, diabetic retinopathy and glaucoma. In addition to eye conditions, cerebral visual impairment (CVI) is also a possibility.

What are the complaints associated with these eye conditions?

What are refraction disorders, macular degeneration, diabetic retinopathy, glaucoma, cataract, strabismus, keratoconus, corneal clouding, microcorneae and cerebral visual impairment and what symptoms do these conditions cause?

• In a refraction disorder the length of the eye from back to front is too long or too short. In myopia or shortsightedness, people can see clearly close up but not from a distance when not wearing glasses. In hypermetropy or long sightedness, people cannot see clearly close up but they can see distant objects clearly when not wearing glasses or lenses.
• Macular degeneration is an impairment in the function of the central part of the retina – the yellow spot or macula – due to the gradual deterioration of the cones. Visual acuity is lost and a spot is left in the centre of the image. The rest of the retina remains intact and so people can continue to find their way around at home and elsewhere more or less independently.
• Diabetic retinopathy is damage to the blood vessels in the retina caused by diabetes. Damage may occur within the eye without being noticed immediately. When the problem is not identified and treated in good time, it can cause visual impairment or blindness.
• Glaucoma is the loss of fibres in the optic nerve as a result of high eye pressure. The damage to the optic nerve causes blind spots (visual field defects) in the image. If treatment is inadequate or absent, the defects in the visual field will worsen and, in the late stage, visual acuity may also be affected. An acute glaucoma causes acute pain, a chronic glaucoma does not.
• A cataract is the clouding of the ocular lens. If the cloudy spot is in the middle of the lens or close to it, problems emerge quickly: blurred vision, double vision, duller colours, problems with light or sparkling. Vision gets steadily worse.
• Strabismus: the eyes do not look in the same direction. Double vision results when the two eyes are not focused on the same spot. If the same eye is crossed all the time, the other eye may become lazy (amblyopic). Vision in that eye will be blurred and there will be no depth of vision.
• Keratoconus is a condition that affects the shape of the cornea: the spherical shape is sagged or the cornea may actually be conical. Because the cornea is the most important refractive medium of the eye, there is a major impact on vision. Keratoconus can result in sensitivity or even pain.
• Corneal cloudiness: the cornea is no longer clear and this can affect vision.
• Microcorneae: the cornea is too small. This condition is usually associated with microphthalmus, in which the entire eyeball is too small, and therefore visual impairment.
• Cerebral Visual Impairment (CVI): is when the cause of the visual impairment is in the visual projection pathways connecting the retina to the visual cortex beyond the optic chiasm or in the visual cortex itself. This type of impaired vision results from limitations in functional visual perception.

How common are these eye conditions in the general population and in people with intellectual disabilities? ^{195 196}

Comments on the prevalence of eye conditions in the general population:

Comments about the prevalence of eye conditions in people with intellectual disabilities:

• Refraction disorders, strabismus, keratoconus and corneal clouding are more common in people with Down syndrome that in other people ^splunder .
  
• Another study of 6220 people with intellectual disabilities in the Netherlands examined by an ophthalmologist found that 37.6% of people with impaired vision had a CVI: 31.2% in people aged between 0 and 20 years and 13.6% in persons aged over 40. ¹⁹⁷