Tests
1st tests to order
assessment of visual acuity
Test
May be measured using a Snellen chart and can be varied depending on the type and severity of RP. It is essential to record visual acuity for both functional and legal implications and to track progress. Refractive errors may be noted, and sight may be improved by glasses if this is corrected, although underlying RP remains.
Result
variable
full field perimetry
Test
Goldmann kinetic perimetry has historically been the method for assessing a patient's full visual field; however, Octopus 900 perimetry is now capable of performing both kinetic and static full field perimetry.
Defects can start as islands in the mid periphery, expand to form crescents, and finally result in a complete ring scotoma. In time, ring scotomas can enlarge, leaving patients with a diminishing tunnel field of vision.
Result
mid-peripheral visual field defects
full field electroretinogram (ERG)
Test
Abnormal ERGs are an essential feature of RP. Decreased amplitude and increased latency can be seen in both the dark-adapted and light-adapted ERGs. Useful in both diagnosis and monitoring progression of disease. ERGs are almost always decreased in patients with RP, but decreased ERGs alone do not make diagnosis because many other nondegenerative inherited diseases can present with ERG changes. ERGs should be measured according to the standards described by the International Society for Clinical Electrophysiology of Vision (ISCEV).[25] Each laboratory must establish normal values from a suitable age-matched population.
Result
decreased scotopic a-wave and b-wave with increased b-wave latencies; decreased photopic a-wave and b-wave, decreased amplitude on photopic 30 Hz flicker with increased latency
Tests to consider
elevated final dark-adapted threshold
Test
Final dark-adapted threshold is measured by fully dark-adapting patients and then measuring the dimmest intensity of light that they can perceive.
Result
mirrors the symptomatic reports of impaired dark adaptation
optical coherence tomography (OCT)
Test
Should be considered in all patients with worsened central visual acuity. OCT of the retina can reveal retinal atrophy and is especially useful for determining the presence of cystoid macular edema.
Result
retinal atrophy, possible presence of cystoid macular edema
genetic testing
Test
Available for only a subset of the total genes in RP, and even testing of known genes is not always completely sensitive. Most effective when a particular gene is suspected. Performed only in certain people after consultation with a clinical geneticist when probability of identifying the responsible gene is good. May also be indicated if an underlying syndrome is suspected. If there are existing genetic test results, do not repeat a test unless there is uncertainty about the existing result, e.g., the result is inconsistent with the patient’s clinical presentation or the test methodology has changed.[23][24]
Guidelines from the American Academy of Ophthalmology give specific recommendations about genetic testing.[26]
Result
confirmation of specific gene defect or identification of underlying syndrome
adaptive optics imaging
Test
Adaptive optics imaging is new technology that allows for high-resolution imaging of the photoreceptor mosaic by compensating for corneal and lenticular aberrations during imaging. Custom-built systems are capable of resolving individual cones and rods in some individuals.
Result
may reveal degeneration of rods and cones
wide-field fundus autofluorescence (FAF)
Test
Relatively new imaging modality that identifies areas of irregular lipofuscin distribution in the retinal pigment epithelium (RPE) cell monolayer of the posterior pole and peripheral retina. Irregular patterns of FAF correlate with retinal disease, retinal pigment changes, and retinal atrophy. Specific patterns of abnormal FAF are useful in the diagnosis of inherited retinal degenerations. Guidelines from the American Academy of Ophthalmology give recommendations for the clinical assessment of patients with inherited retinal degenerations.[24]
Result
correlates with disease-specific patterns of retinal degeneration
Emerging tests
whole exome sequencing
Test
Whole exome sequencing is now becoming available and allows testing of many genes at one time. This technology offers the hope of finding new genes for RP. If there are existing genetic test results, do not repeat a test unless there is uncertainty about the existing result, e.g., the result is inconsistent with the patient’s clinical presentation or the test methodology has changed.[23][24]
Result
may reveal novel genes for RP
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