Causes of visual impairment

Information on Visual Impairment

Visual system may be affected by numerous different diseases, defects, problems, infections, disorders and malformations. Visual impairment is just one of the numerous different medical conditions and it can be caused by other underlying medical conditions.

One of the most common causes of visual impairment is a cataract. Cataracts are a clouding of the eye lenses and they can be caused by trauma, certain types of diseases or they can be congenital. They need to be as early as the medical factors allow it. Cortical visual impairment is a medical condition characterized by a visual reduction caused by problems in the brain cortex.

Glaucoma is another medical condition that can be a potential cause of visual impairment. It is characterized by by abnormal fluid production/drainage rate which causes intraocular pressure. In most cases, it needs to be treated by a surgical procedure. There are also numerous different types of infections that may affect the eyes and cause visual impairment among the variety of many other symptoms. Conjunctiva and certain other systemic infections are the most common ones to occur. Numerous different malformations can also lead to an impaired vision.

Visual impairment (VI) is a major health problem worldwide. According to the World Health Organization (WHO) estimations, 285 million visually impaired people lived in the world in 2010 which included 39 million blind people and 246 million subjects with low vision. Visual problems impose large costs on the society. Nowadays, living standards have been improved in most communities, but the prevalence of avoidable blindness remains significantly high in many countries. Almost 80% of global VI is treatable or preventable. Cataracts and uncorrected refractive errors have been accounted as the leading causes of VI, and the major cause of blindness is cataract.

Data on the prevalence and causes of VI and blindness is required to plan programs for eliminating avoidable blindness and VI. About 90% of the world's visually impaired subjects, live in developing countries.
A number of studies have reported the prevalence of VI and blindness in Iran, but no population-based study data is available from central Iran. This population-based study was performed in Yazd district to determine the prevalence and causes of VI and blindness in the central region of Iran.
This population-based cross-sectional study was conducted in 2010–2011 on adults aged 40–80 years in both urban and rural area of Yazd district. Yazd is located in central Iran and has an estimated population of 526,000 people according to the 2006 national census. The study adhered to the Declaration of Helsinki and was approved by the Ethics Committee at Shahid Beheshti University of Medical Sciences. All eligible subjects signed an informed consent.
Out of 2,320 eligible individuals, 2,098 participated in the study (90.4% response rate), of whom, 2,023 subjects completed all evaluations. The standardized prevalence of blindness and VI were 0.7% (95% confidence interval [CI], 0.3–1.0%) and 4.4% (95% CI, 3.3–5.4%), respectively which was significantly associated with older age (odd ratio [OR] = 3.2, 95% CI: 1.9–5.2 and OR = 3.1, 95% CI: 2.3–4.2, respectively) and female sex (OR = 3.6, 95% CI: 1.1–12.3 and OR = 1.7, 95% CI: 1.2–2.5, respectively). The proportion of avoidable causes of blindness and VI were 92.9% (95% CI: 80.0-100.0%) and 76.6% (95% CI: 69.2-85.0%), respectively. Major causes of blindness were diabetic retinopathy (50.0%), glaucoma (21.4%) and cataracts (14.3%) whereas main causes of VI were cataracts (41.5%), diabetic retinopathy (17.0%) and age-related macular degeneration (13.8%).

✓ Fact confirmed: Prevalence and Causes of Visual Impairment and Blindness in Central Iran; The Yazd Eye Study Marzieh Katibeh, Mohammad Pakravan, Mehdi Yaseri, Mojgan Pakbin, and Reza Soleimanizad; 2015 Jul-Sep

The most common malformations may include clefts in the iris, syndrome related abnormalities and dislocated lens. Numerous different problems that may affect the ocular muscles can also lead to conditions which may involve visual impairment. The most common problem is called strabismus and it involves misalignment of the eyes. Involuntary eye movements are medically referred to as nystagmus and they can also be associated with visual impairment in some cases.

Different types of ocular traumas can also be held responsible for the impaired vision in some patients. Most common ones include condition in which the eyeball gets lacerated, hit or punctured. These conditions usually require immediate medical attention.

Optic Nerve Defects

Numerous different defects of the optic nerve may also occur and some of them may be the cause of visual impairment in some cases. The most common defect is called optic atrophy and it involves improper functioning of the optic nerve. Some rare cases involve septo-optic dysplasia which is the extreme form of the optic nerve hypoplasia. The common refractive errors such as astigmatism, farsightedness and nearsightedness can also be possible causes of visual impairment.

Another medical condition that may be associated with visual impairment is called retinoblastoma. It is characterized by a tumor which is located behind the eye and it can be very dangerous, even fatal in some cases. Other causes of visual impairment may include retinopathy of prematurity and certain other syndrome related visual dysfunctions and ocular abnormalities.