Inherited retinal dystrophies
Non progressive dystrophies
Congenital stationary night blindness
Progressive dystrophies
X linked juvenile retinoschisis
There are a large number of inherited retinal dystrophies, caused by damage to the light receptors (sensory nerve endings that respond to light) in the retina, which cause symptoms in childhood. Most are associated with a gradual deterioration in vision over time, but some are non progressive. They are all relatively uncommon. Some of the more common are described below.
Non progressive dystrophies
Congenital stationary night blindness
Congenital stationary night blindness (CSNB) – may be autosomal dominant, autosomal recessive or X linked. Children with the autosomal dominant type have poor night vision but vision is otherwise normal. Children with the autosomal recessive and X linked type have moderately reduced visual acuity and mild colour vision disturbance.
Achromatopsia
There are two main types. Children with the autosomal recessive type (rod monochromatism) in which there are no functioning cone receptors in the retina present in infancy with reduced vision, severe photophobia (intolerance to light) and nystagmus (jerking movements of the eyes). Visual acuity is usually about 6/60 and these children have no colour vision. Children with the less common X linked type (blue cone monochromatism) have blue cones in the retina. They have better visual acuity than children with the autosomal recessive type and have some colour vision.
Progressive dystrophies
These are classified according to whether they affect the retina generally or the central retina.
Generalised
Infantile rod cone dystrophy (Leber’s amaurosis)
Children with this condition present in infancy with severe visual impairment, nystagmus and roving eye movements. Most children are otherwise normal but some may have developmental delay and other neurological problems.
Retinitis pigmentosa
Retinitis pigmentosa may be autosomal dominant, autosomal recessive or X linked and is associated with characteristic pigmentation of the retina. The age of onset and prognosis is very variable. X-linked recessive disease tends to be of early onset and severe, autosomal dominant tends to be of later onset with a better visual prognosis and autosomal recessive is very variable. Retinitis pigmentosa is also associated with a variety of inherited genetic syndromes, for example Usher syndrome (associated deafness) and Refsum disease (associated unsteadiness, peripheral nerve damage and deafness). In the majority of these syndromes, treatment does not have any effect on the progression of the visual impairment. However, in Refsum disease, dietary modification may slow the deterioration in visual impairment.
Children with retinitis pigmentosa usually present with difficulties with night vision and peripheral field loss. There is usually subsequent progressive visual field loss resulting in marked constriction of the visual field and there may be central field loss as well if the macula is affected.
Retinitis pigmentosa is associated with cataracts and oedema (swelling of the macula). Although there is no specific treatment for retinitis pigmentosa itself, vision may be improved by treating the cataracts or macular oedema.
Central retina
X linked juvenile retinoschisis
This is the most common inherited retinal dystrophy affecting males and is due to splitting of the layers of the retina. It usually presents in childhood with reduced visual acuity. It is often discovered on routine testing, but may present with sudden visual loss secondary to vitreous haemorrhage (bleeding into the vitreous at the back of the eye). In the long term, vision is usually reasonably well preserved, but severe visual loss may occur if there is extensive involvement of the peripheral retina or if there is vitreous haemorrhage or retinal detachment.
Stargardt disease
Children with this condition have degeneration of the macula resulting in central visual field loss, although later in the disease they may have peripheral field loss as well. They usually develop symptoms during their school years but some may not present until early adult life. The prognosis is poor and most have a visual acuity of 6/60 or less by their early 20s.
Vitelliform dystrophy (Best disease)
This condition usually presents with mild visual loss in childhood or early adult life. The visual prognosis is generally good but there are some people who develop subretinal neovascularisation (new blood vessel formation in the retina) that may result in significant visual impairment.
Progressive cone dystrophies
There are many different types of varying severity. Children have early loss of colour vision, photophobia, reduced visual acuity, nystagmus in the early onset forms and most develop night blindness. Although there is variation in severity, overall the visual prognosis is poor.
