As stated above, the symptoms of LCA are typically noticed very early in a child’s life—in the first weeks or months after birth. Parents may observe that the child does not focus on things in the surrounding environment, or they may notice “wibbly” back-and-forth movements of the call called “nystagmus.” Some children may even press or push on their eyes with their fingers or fist. During an eye exam, the child’s retina may not look different than a normal one, but further testing will reveal that the eye and brain are not communicating they way they should.
Children with LCA usually have severe vision loss of 20/400 or worse, meaning that they can see at 20 feet what a person with “normal” vision can see at 400 feet. Some children may have only light/dark perception, and in fewer cases no vision at all. Children with some vision may have other symptoms such as night blindness, light sensitivity, and far-sightedness.
There are rare genetic syndromes that mimic LCA vision loss in young children, including Alström syndrome, Batten disease, Joubert syndrome, and peroxisomal diseases (Zellweger syndrome or Refsum disease). Children with these conditions have vision loss similar to LCA, as well as other physical or mental disabilities. A child diagnosed with true LCA (not one of the syndromes listed above) may, in rare cases, be more vulnerable to kidney disease than other children. Compared to the general population, however, they do not have a greater risk of either intellectual disabilities or autism.
An ophthalmologist may suspect LCA on the basis of a child’s symptoms and the findings of a simple eye examination. Two tests can be used to clarify the diagnosis:
- ERG (electroretinography): this is a test that measures the electrical responses of the retina to light, evaluating responses of both rod and cone photoreceptors. The ERG test involves staying in a darkened room for 30 minutes, with drops put into the eye or eyes being tested. A special contact lens or gold-foil electrode is then placed on the eye or lower eyelid, and the eye is exposed to flashes of light.
- OCT (optical coherence tomography): this is an imaging technique that involves taking digital images of the various layers of the retina. The process is uses light rather than sound or radio waves, which is why the images are in high resolution.
- Genetic counselling: while not a test in the traditional diagnostic sense, genetic counselling is an important part of the diagnostic process. It can help determine the gene or genes that have been mutated, as well as the hereditary factors that are involved.