Investigations
1st investigations to order
electroretinography (ERG)
Test
ERG measures the electrical activity of the retina. This is a first-line investigation, usually performed by a specialist ophthalmic unit.[28] ERG shows the classic changes of vitamin A (retinol) deficiency as loss of, or reduced, a- or b-wave amplitudes.[26] Congenital stationary night blindness can cause an electronegative ERG pattern.[27]
Result
pattern of electrical activity produced in the retina may indicate the cells affected by the underlying disease process
slit-biomicroscopy and indirect ophthalmoscopy
Test
The best method of examining the optic disc is with the slit lamp combined with a high-magnification posterior pole lens.
Result
allows detailed examination of the peripheral retina and choroid; findings vary depending on the underlying cause of the night blindness. Vitamin A (retinol) deficiency may cause dry eyes, bitot’s spots on the conjunctiva, and pigmentary retinopathy. Patients with retinitis pigmentosa may have cataract formation, typical pigmentary retinopathy with bony-spicules, and a waxy-pale optic disc. The fundus may have a normal appearance in congenital stationary night blindness.
Investigations to consider
serum vitamin A (retinol) level
Test
Measurement of serum vitamin A (retinol) may be indicated if the patient has a known risk factor for deficiency, or if ERG indicates deficiency as a possible underlying cause for night blindness.
A number of different laboratory investigations are available for testing clinical and subclinical vitamin A (retinol) deficiency.[29]
Result
retinol levels may be normal or low; however, clinical examination and ERG finding will usually help make the diagnosis
next-generation-sequencing
Test
Usually done after referral to a clinical genetics service. Next-generation-sequencing provides a much faster and more detailed analysis of DNA/RNA sequencing and mutations. It can also be used, at the geneticist’s discretion, for more accurate testing of specific genetic mutations associated with hereditary conditions.[24]
Result
establishes the mode of inheritance which may give an indication of the prognosis
Use of this content is subject to our disclaimer