X-linked recessive

Corneal opacification is severe in males and has been described as resembling ground glass, or having a milky white appearance throughout the entire cornea.  Corneal clouding may be seen in infants but progresses with age in most cases.  In a 7 generation Austrian family, nine males had severe corneal opacification, seven with band keratopathy and 2 with the typical ground glass appearance.  Vision may be 20/20 even in adults but the majority have acuities in the range of 20/30 to 20/60 even into the 7^th decade.  A few have vision of 20/100 to 20/400 even as young adults and one 19 year old was reported with nystagmus.  The corneas of twenty-two females and four males were said to have only a 'moon crater-like' appearance resulting from focal discontinuities in the endothelial layer.  Tissue studies of a keratoplasty button from a 60 year old male revealed endothelial degeneration and thickening of the Descemet membrane.  There may also be irregular thinning of the epithelial and Bowman layers.

This is an X-linked disorder in which males have a variety of ocular defects.  The fundus is hypopigmented and the fovea is incompletely developed.  The hypopigmentation is most pronounced in the posterior pole and peripapillary region.  Variable degrees of iris transillumination have also been noted.  Progressive axial myopia, nystagmus, astigmatism, defective night vision, and a protan color vision defect are additional cardinal features.  Females may be mildly affected with subtle nystagmus and color vision defects.  It is sometimes mislabeled as X-linked albinism (OA1, #300500) but differs importantly from that disorder by the lack of misrouting of optic nerve axons.  The eponymic label 'Forsius-Eriksson type ocular albinism' further adds to the confusion with ocular albinism. 

X-linked Alport syndrome is a basement membrane disease with important ocular manifestations.  The lens is usually normal at birth but lens opacities eventually occur in a significant number of individuals with the most characteristic type being anterior polar in location.  Involvement of the anterior lens capsule often results in bilateral anterior lenticonus (25%) and may be progressive.  It is claimed that the severity of the lenticonus is a valuable marker in judging the overall disease severity.  In early stages it may be difficult to detect but its presence is suggested by an 'oil droplet' reflex during retinoscopy or slit lamp examination.  All males with anterior lenticonus should be evaluated for Alport syndrome. 

Posterior polymorphous corneal dystrophy and posterior subcapsular opacities have also been noted.  The defect in basement membranes may lead to recurrent corneal erosions, even in children, which can be incapacitating and difficult to treat.  Involvement of Bruch's membrane has been considered the source of retinal pigment epithelial changes described as a flecked retina, or 'fundus albipunctatus', found in 85% of patients.  More recent evidence using OCT suggests that the dot-and-fleck retinopathy results primarily from abnormalities in the internal limiting membrane and the nerve fiber layer.  The yellowish and/or whitish flecks are most commonly located in the posterior pole and particularly in the macula.  There is no night blindness or visual impairment from the retinal involvement.  Fluorescein angiography shows patchy areas of hyperfluorescence.  The amount of visual impairment depends primarily on the extent of lens involvement.

Termporal macular thinning occurs to some extent in all types of Alport syndrome based on OCT findings.   In one series all patients with X-linked disease had temporal thinning suggesting that this might be a useful diagnostic sign.  However, similar thinning is also seen in Leber hereditary optic neuropathy (535000), and dominant optic atrophy (165500).

Choroideremia is characterized by a progressive atrophy of photoreceptors, retinal pigment epithelium (RPE) and choroid. Areas of RPE atrophy are present early in the mid-periphery and progress centrally.  This is associated with loss of photoreceptors and the choriocapillaris.

Night blindness is the first symptom often with onset during childhood. A ring-like perimacular scotoma develops that progresses into the periphery during life with corresponding visual field loss (peripheral constriction).  Symptoms and fundus changes are highly variable. Visual acuity is generally well maintained into later stages of the disease but some males are blind by age 30 years whereas others over the age of 50 are symptom-free.  An increased prevalence of myopia has been noted.

Males with choroideremia (and some females) have progressive loss of the choriocapillaris eventually baring the sclera beneath. Female carriers can exhibit patchy areas of RPE atrophy in the periphery and these may enlarge. Female carriers are typically not symptomatic, but there are reports of females being fully affected.  Females may also have visual field changes and defective dark adaptation.  OCT in young women shows dynamic changes and remodeling of the outer retina with time with focal retinal thickening, drusenlike deposits and disruptions in photoreceptor inner and outer segment junctions even in younger individuals.  The phenotype is more severe in older females as well suggesting that the retinal degeneration is progressive in both sexes.

Electroretinography (ERG) initially shows a decreased dark-adapted response with  intact light-adapted responses, indicating general dysfunction of rod photoreceptors. Cone dysfunction, however, develops with progression of the disease.

Congenital nystagmus is a feature of numerous ocular and systemic disorders.  Isolated idiopathic congenital nystagmus (CN), however, refers to a diverse group of abnormal eye movements which are identified usually in the first 6 months of life when no other ocular abnormalities are present.  Horizontal eye movements are typical, but vertical and rotary eye movements have also been reported.  If the nystagmus is horizontal, the eye movement is usually "to-and-fro".   In general, as the patient gets older, the amplitude of the nystagmus decreases and the frequency of the nystagmus increases, particularly when the patient tries to fixate or look directly at an object. This nystagmus can increase in size and frequency when the patient is tired, sick, or fatigued.  Some very young patients are noted to have head nodding or head shaking, but these usually disappear over time. Vision is reduced and varies through the day. Balance may also be affected.  Many patients have a "null point" where the eye movement is reduced and vision is improved.  They may alter their head position in an effort to maximize their acuity.

Strabismus and amblyopia often develop.