Retinitis Pigmentosa Diagnosis

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By Dr Ananya Mandal, MD

Retinitis pigmentosa is commonly identified by the examination of the appearance of the retina using slit lamp biomicroscopy. Common findings on examination and steps in diagnosis include:-

The retina shows black or dark brown, star-shaped concentrations of pigmentation. The pigmentation may be limited to part of the retina or involve the whole retina. Abnormalities may appear to be radiating out from the disc. In association there may be abnormalities of the blood vessels as well. Slit-lamp biomicroscopy is the key initial assessment.
Imaging studies of the eyes include Retinal photography, ultrasound of the eye, Fluorescein angiography to check the status of the eye blood vessels and Optical computer tomography.
The most critical diagnostic test is the electroretinogram (similar to the ECG or electrocardiogram of the heart or EEG or electroencephalogram of the brain). This looks at the electric activities of the nerves within the retina.
Other tests include those for visual acuity (refraction tests), Visual field assessment, assessment of Pupillary reflex, assessment of color blindness and intraocular pressure determination.
There may be associated problems in the eyes that may be found using appropriate diagnostic tools. These include:
- Myopia or short sightedness - this is seen frequently and is identified using refraction tests of the eyes.
- Subcapsular cataract – this may be identified using slit lamp biomicroscopy and examination of the lens.
- Open angle glaucoma - this is seen in 3% cases of retinitis pigmentosa and is identified by measuring the intraocular pressure using tonometry devices.
- Changes in the vitreous humor (commonly posterior vitreous detachment) seen on slit lamp biomicroscopy.
There may be associated problems seen on other organs as well. These are part of the retinitis pigmentosa syndrome. These are seen in 20 to 30% cases and are identified while diagnosing the condition. At least 30 different associated syndromes have been identified. Some of these include;
- Usher’s syndrome – Retinitis pigmentosa along with hearing loss. This accounts for about half of all cases of combined deaf-blindness.
- Loss of hearing along with vision loss of retinitis pigmentosa is also seen in other syndromes such as Waardenburg's syndrome, Alström's syndrome, Alport's syndrome, Refsum's syndrome etc. These have different manifestations as well.
- Bardet-Biedl syndrome or Laurence-Moon syndrome is associated with retinitis pigmentosa along with features like short height, kidney dysfunction and polydactyly (extra fingers of toes).
- Hurler's syndrome, Scheie's syndrome, Sanfilippo's syndrome is associated with mucopolysaccharidoses along with retinitis pigmentosa.
- Kearns-Sayre syndrome is a mitochondrial disorder where retinitis pigmentosa is found along with ptosis (droopy eyelid), opthalmoplegia (vision problems) and heart block.
Diagnoses that mimic retinitis pigmentosa need to be ruled out - these include Friedreich's ataxia, trauma to the eye, oxalosis, glaucoma, End-stage Chloroquine or thioridazine or syphilis related neuroretinitis and cancer related retinopathy.
Genetic testing for possible mutation that led to the condition is available for 11 possible genetic mutations. Genetic assessment and counselling may be offered to select patients.