It’s almost always what you think it is, until it’s not.
Rare eye conditions pose quite the 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,” he says
“A misdiagnosis can cause undue harm.”
Photo description: Eye health professional points to an eye chart.
Leber’s hereditary optic neuropathy
Summary: Leber’s hereditary optic neuropathy (LHON) is a genetically inherited vision condition that affects young adults’ central vision and can result in lifelong blindness.
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.
Summary: 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.
- 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
Summary: 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.
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
Summary: 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.
- Thinning of cornea
- Blue tint to the sclera
- Retinal detachment
Some experience musculoskeletal disease symptoms, including scoliosis, hip dysplasia, muscle weakness, and foot deformities.
Cause: Genetic disease
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 
Summary: 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.
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
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.
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.
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.
To find out more visit visionaustralia.org/referral.
 Source: National Organization for Rare Disorders “Leber Hereditary Optic Neuropathy” https://rarediseases.org/rare-diseases/leber-hereditary-optic-neuropathy/
 Source: National Organization for Rare Disorders “Usher Syndrome”
Better Health Channel, Victorian Government, Conditions and Treatments, “Usher Syndrome”
 Sources: Bardet Bield syndrome foundation “What is BBS?”
National Organization for Rare Disorders, Rare Diseases, “Bardet-Biedl Syndrome”
 Source: National Centre for Advancing Translational Sciences, Genetic and Rare Diseases Information Centre “Brittle cornea syndrome”
Ehlers Danlos News “Brittle Cornea Syndrome”
 Source: National Organization for Rare Disorders, Rare Diseases, “Optic Nerve Hypoplasia”
The Magic Foundation, Growth Disorders, “Optic Nerve Hypoplasia”