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Introduction

It’s almost always what you think it is, until it’s not. Rare eye conditions pose quite a challenge for eye health practitioners. Australia’s diversity also means practitioners need to know common and rarer eye conditions from all over the world. Vision Australia Orthoptist Cem Oztan says it’s important to think outside the box when diagnosing patients, and be aware that common symptoms can mask rarer conditions. 

“Patients must be given the right treatment plan for the best outcomes... A misdiagnosis can cause undue harm.”

— Cem Oztan, Vision Australia Orthoptist

Leber’s hereditary optic neuropathy

Leber’s hereditary optic neuropathy (LHON) is a genetically inherited vision condition that affects young adults’ central vision and can result in lifelong blindness.

Symptoms

Loss of central vision including blurring and reduced perception of colour.  Vision loss begins in one eye first then progresses to the other eye after two to three months. Usually affects young adults, before the age of 40.

Cause

Genetic mutation (strictly transmitted by maternal inheritance)

Prevalence

Approx. 1:50,000 people

Unique traits

Males are about four to five times more likely than females to lose vision and be affected.

Similar conditions

Autosomal dominant optic atrophy (DOA) - symptoms tend to come on earlier than in LHON, generally before puberty, toxic/nutritional optic neuropathies, Multiple Sclerosis, LHON plus. 

Treatment

Current treatments address the symptoms, eg. vision aids and orientation and mobility training for vision loss.

Usher’s syndrome

Usher’s syndrome refers to a group of genetic conditions that have both hearing loss and progressive deterioration in vision due to retinitis pigmentosa (RP). It causes a gradual decline in vision because two types of photoreceptor cells, known as the rod and cone cells, begin to degenerate and die.

Symptoms

Hearing loss (usually from birth) then vision loss from retinitis pigmentosa. Problems with balance. Difficulty in seeing in the dark, tunnel vision, reduced acuity and loss of colour perception.

Cause

Genetic disease (inherited retinal dystrophy).

Prevalence

1:10,000 people

Unique traits

Usher’s syndrome is responsible for the majority of cases of deaf-blindness.

Similar conditions

Retinitis pigmentosa (Usher syndrome is reserved for patients where the hearing loss becomes obvious at a very early age).

Treatment

Current treatments address the symptoms, eg. hearing aids for hearing loss, vision aids and orientation and mobility training for vision loss. Gene therapy research is proving promising.

Bardet Biedl syndrome

Bardet-Biedl syndrome (BBS) affects several aspects of a patient, most notably vision impairment due to retinal dystrophy. Patients also may have extra fingers or toes, kidney dysfunction, obesity and learning difficulties.

Symptoms

Difficulty in seeing in the dark, development of blind spots in vision, tunnel vision, reduced acuity and loss of colour perception. Other symptoms include: Extra fingers or toes. Obesity in childhood Abnormalities of the genitalia and infertility due to hypogonadism Learning disorders

Cause

Genetic disease (inherited retinal dystrophy)

Prevalence

1:250,000 people

Unique traits

Some people with BBS lose most of their vision by their mid-teens, but others have maintained enough vision to drive into their 30s. More common in Canada and Middle Eastern populations.

Similar conditions

Variety of inherited retinal dystrophies (ie: rod/cone dystrophy, etc), Prader-Willi Syndrome, Laurence-Moon syndrome. Treatment: Current treatments address the symptoms, eg. vision aids, orientation and mobility training, weight management, speech therapy etc.

Brittle Cornea Syndrome

Brittle cornea syndrome (BCS) is a form of Ehlers-Danlos syndrome involving the connective tissue in the eyes, ears, joints and skin. It is characterised by extreme thinning of the outer layer of the eye (cornea) which may lead to tearing or rupture with just minor injury, which can progress to blindness.

Symptoms

Thinning of cornea Blue tint to the sclera Myopia Retinal detachment Some experience musculoskeletal disease symptoms, including scoliosis, hip dysplasia, muscle weakness, and foot deformities.

Cause

Genetic disease

Prevalence

<1/1,000,000

Unique traits

Symptoms can occur as early as two years of age.

Similar conditions

Keratoconus, many forms of Ehlers-Danlos syndrome, Marfan syndrome, osteogenesis imperfect.

Treatment

Current treatments address the symptoms, eg. vision aids, orientation and mobility training. Corneal rupture can be avoided by using protective, polycarbonate spectacles.

Optic Nerve Hypoplasia

Optic Nerve Hypoplasia (ONH) is a condition where a child has under-developed optic nerves. It can occur on its own or in conjunction with central nervous system abnormalities. 

Symptoms

Abnormal eye movements (nystagmus) Vision can range from no light perception to good functional vision, or even full vision in one eye. Other symptoms include: Visual field loss Pituitary problems Hormone abnormalities Developmental delay Cause: unknown

Prevalence

1:10,000 children

Unique traits

ONH is present at birth, but many symptoms may not be apparent until childhood, or even adolescence. Vision often improves modestly in early childhood even though there is no growth of the optic nerves after birth.

Similar conditions

Differentiating ONH as in isolation or part of central nervous system abnormalities (septo-optic dysplasia, holoprosencephaly).

Treatment

Current treatments address the symptoms, eg. vision aids, orientation and mobility training.

What's next

There aren’t many cures or therapies for these diseases. So it is important to refer patients to worthwhile vision services as soon as possible to make sure they get the best outcomes. 

Refer a patient

A wide variety of vision services, including orthoptic functional vision assessment and low vision aid prescription, assistive technology support and orientation and mobility training is available at Vision Australia.