Lesser Known Disorders
Each issue of this series contains at least three lesser known disorders. Some of these disorders may contain subtypes which will also be presented. You will also notice that each disorder has a code. These codes represent the coding system for all disabilities and disorders listed in the Educator’s Diagnostic Manual(EDM) Wiley Publications.
Disorders in this issue:
VI 3.12-Optic Nerve Atrophy (Second cranial nerve atrophy)
Disability Category: Visual Impairments
Definition
Optic nerve atrophy involves tissue death of the nerve that carries the information of vision from the eye to the brain (U.S. National Library of Medicine, 2004).
Explanation
There are many unrelated causes of optic atrophy. The optic nerve can also be damaged by shock, various toxic substances, radiation, and trauma. Various eye diseases, glaucoma most commonly, can also cause optic nerve atrophy. In addition, the condition can be due to the effects of diseases of the brain and central nervous system, such as multiple sclerosis, brain tumor, and stroke. There are also several rare forms of hereditary optic nerve atrophy that affect children and young adult. Optic nerve atrophy causes dimming of vision and reduction of the field of vision(U.S. National Library of Medicine, 2004).
VI 3.13-Optic Nerve Hypoplasia
Disability Category: Visual Impairments
Definition
Hypoplasia” means smaller than normal. Optic nerve hypoplasia (ONH) refers to small or underdevelopment of the nerve which transmits vision signals from the eye to the brain. This is usually associated with permanent vision loss, which may be mild or severe. ONH may affect either one or both eyes (American Association for Pediatric Ophthalmology and Strabismus, 2005a).
Explanation
Vision can range from near-normal levels to severe impairment. Children with ONH may have precisely difficulty locating objects, due to a constricted visual field or impaired depth perception. Some children have light sensitivity.
If vision is significantly affected in both eyes, an infant will present with poor vision or shaking of the eyes (nystagmus). If only one optic nerve is small, the eye may cross in or drift out (American Association for Pediatric Ophthalmology and Strabismus, 2005a).
VI 3.14-Retinitis Pigmentosa (RP)
Disability Category: Visual Impairments
Definition
Retinitis pigmentosa is a progressive degeneration of the retina (part of the eye) which affects night vision and peripheral vision (U.S. National Library of Medicine, 2004).
Explanation
Retinitis pigmentosa commonly runs in families. The disorder can be caused by defects in a number of different genes which have recently been identified.
The cells controlling night vision, called rods, are most likely to be affected. However, in some cases, retinal cone cells are most damaged. The hallmark of the disease is the presence of dark pigmented spots in the retina(U.S. National Library of Medicine, 2004).
VI 3.14a -Autosomal dominant inheritance
In families with the autosomal dominant RP, an affected parent can have both affected and unaffected children. The patient has one gene for retinitis pigmentosa paired with one normal gene and has a 50% chance of passing the disease to their child, even if their partner is unaffected.
VI 3.14b -Autosomal recessive inheritance
In families with autosomal recessive Retinitis Pigmentosa, unaffected parents can have both affected and unaffected children. There may not be a known family history of the disorder. Both parents have normal retinas and carry a defective gene. There is a 25% chance that their child will be afflicted.
VI 3.14c -X-linked inheritance
In families with the X-linked type, only males are affected, while females carry the genetic trait but do not experience serious vision loss.
VI 3.16-Retinopathy of Prematurity (ROP) – (Retrolental fibroplasias)
Disability Category: Visual Impairments
Definition
Retinoblastoma Retinopathy of prematurity (ROP) is a potentially blinding eye disorder that primarily affects premature infants weighing about 2¾ pounds (1250 grams) or less that are born before 31 weeks of gestation (A full-term pregnancy has a gestation of 38–42 weeks) (National Eye Institute, 2005).
Explanation
The smaller a baby is at birth, the more likely that baby is to develop ROP. This disorder—which usually develops in both eyes—is one of the most common causes of visual loss in childhood and can lead to lifelong vision impairment and blindness. ROP was first diagnosed in 1942.
ROP occurs when abnormal blood vessels grow and spread throughout the retina, the tissue that lines the back of the eye. These abnormal blood vessels are fragile and can leak, scarring the retina and pulling it out of position. This causes a retinal detachment. Retinal detachment is the main cause of visual impairment and blindness in ROP.
ROP is classified in five stages, ranging from mild (stage I) to severe (stage V). Most babies who develop ROP have stages I or II. However, in a small number of babies, ROP worsens, sometimes very rapidly. Untreated ROP threatens to destroy vision (National Eye Institute, 2005).
ROP is classified in five stages, ranging from mild (stage I) to severe (stage V):
VI 3.16a Stage I -Mildly abnormal blood vessel growth.
Many children who develop stage I improve with no treatment and eventually develop normal vision. The disease resolves on its own without further progression.
VI 3.16b Stage II-Moderately abnormal blood vessel growth.
Many children who develop stage II improve with no treatment and eventually develop normal vision. The disease resolves on its own without further progression.
VI 3.16c Stage III-Severely abnormal blood vessel growth.
The abnormal blood vessels grow toward the center of the eye instead of following their normal growth pattern along the surface of the retina. Some infants who develop stage III improve with no treatment and eventually develop normal vision.
VI 3.16d Stage IV-Partially detached retina.
Traction from the scar produced by bleeding, abnormal vessels pulls the retina away from the wall of the eye.
VI 3.16e Stage V-Completely detached retina and the end stage of the disease.
If the eye is left alone at this stage, the baby can have severe visual impairment and even blindness.
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