Differentials
Congenital rubella
SIGNS / SYMPTOMS
Granular pigmentary changes on funduscopy. These tend to be more granular than the bone spicules seen in RP, but funduscopy alone cannot reliably distinguish the difference. Congenital deafness may also be present. Other features include microcephaly, intellectual disability, microphthalmia, and congenital cataracts.
INVESTIGATIONS
Normal electroretinogram (ERG).
Positive blood test for rubella antibodies confirms infection.
Syphilis
SIGNS / SYMPTOMS
Pigmentary changes, evidence of retinal vasculitis (such as sheathed vessels), and placoid (plate-like) areas of chorioretinal inflammation. Other features include a firm painless chancre at the site of infection, skin rash, and general symptoms of fatigue, weight loss, and lymphadenopathy.
In congenital syphilis there may be a rash, swollen liver, anemia or jaundice, and rhinitis.
INVESTIGATIONS
Serum Venereal Disease Research Laboratory test (VDRL) will be positive.
Serum rapid plasma regain test (RPR) will be positive.
Vitamin A deficiency
SIGNS / SYMPTOMS
Presents with night blindness and malnutrition. Particularly seen in pregnant women in developing countries.
INVESTIGATIONS
Reversibility of night blindness with high-dose vitamin A supplementation.
Ophthalmic artery occlusion
SIGNS / SYMPTOMS
Sudden-onset, severe, unilateral but painless loss of vision. May have history of amaurosis fugax.
INVESTIGATIONS
Fundus angiography showing impaired choroidal perfusion.
Carotid Doppler scans demonstrating high-risk plaques.
Posterior uveitis
SIGNS / SYMPTOMS
A greater degree of inflammation and signs of chronic inflammation such as posterior synechia, choroidal infiltrates in active phase, asymmetric changes, and presence of vascular cuffing indicating vasculitis.
INVESTIGATIONS
Elevated WBC/CRP and ESR, nonspecific markers of inflammation.
Further tests depend on likely underlying cause: Lyme titer (can cause uveitis in endemic areas); PPD test (positive for patients with suspected tuberculosis); antinuclear cytoplasmic antibodies positive in 90% of patients with granulomatosis with polyangiitis.
Retinal detachment
SIGNS / SYMPTOMS
May have history of risk factors, including ocular trauma, previous detachment, or cataract surgery. History of sudden-onset central visual loss, possibly with preceding flashes of light. On examination there is subretinal fluid and cystic degeneration in an asymmetric pattern.
INVESTIGATIONS
Slit-lamp exam and indirect ophthalmoscopy: retinal detachment; retinal break; vitreoretinal pathology (traction or presence of pigment).
Diffuse unilateral subacute neuroretinitis
SIGNS / SYMPTOMS
Usually a unilateral condition; patient may report floaters or conjunctivitis in the early stages with mild visual loss. More severe visual loss and central scotomas may be evident in later disease. On funduscopic exam crops of yellow creamy-appearing choroidal infiltrates can be seen in the active phase, caused by a nematode worm. Late changes are indistinguishable from RP.
INVESTIGATIONS
Funduscopic exam is usually sufficient.
Scanning laser ophthalmoscope: an infrared laser that is good for identifying live worms in young patients.
Autoimmune retinopathy
SIGNS / SYMPTOMS
Symptoms depend on whether rods or cones are predominantly affected and are clinically indistinguishable from RP. On funduscopic exam there is retinal vascular atrophy but without pigmentary changes.
INVESTIGATIONS
Positive serum antiretinal antibodies.
Congenital stationary night blindness
SIGNS / SYMPTOMS
Relatively normal-appearing fundus; night blindness is nonprogressive. High myopia and nystagmus are frequent features.
INVESTIGATIONS
Decreased b- to a-wave ratio on ERG.
Genetic testing confirms diagnosis.
Fundus albipunctatus
SIGNS / SYMPTOMS
Also presents with symptoms of night blindness but on examination there are small white spots on the retina.
INVESTIGATIONS
Elevated final dark-adapted threshold: impaired dark adaptation that recovers with prolonged time in the dark.
Genetic testing confirms diagnosis.
Achromatopsia
SIGNS / SYMPTOMS
Typically diagnosed at about 6 months of age. Decreased visual acuity with photophobia and complete color blindness. Nystagmus becomes less noticeable with age.
INVESTIGATIONS
Severely diminished photopic ERG but normal scotopic ERG.
Genetic testing confirms diagnosis.
X-linked retinoschisis
SIGNS / SYMPTOMS
Variable history can be mild gradual loss of central vision or sudden severe visual loss with a vitreous hemorrhage. Foveoschisis (splitting of the retinal layers) can appear similar to cystoid macular edema on funduscopy. Peripheral retinal schisis may also be seen.
INVESTIGATIONS
Decreased b- to a-wave ratio on ERG. Demonstration of foveoschisis on optical coherence tomography
Choroideremia
SIGNS / SYMPTOMS
X-linked disorder, so usually only males are affected. Extensive chorioretinal atrophy with sparing of the macula until late stages. Normal-appearing retinal vessels and optic nerve.
INVESTIGATIONS
Genetic testing confirms diagnosis.
Gyrate atrophy
SIGNS / SYMPTOMS
Total blindness usually occurring in middle age (40-60 years).
Peripheral areas of chorioretinal degeneration in gyrate patterns.
Associated with early-onset cataract requiring surgery by 18-20 years of age.
INVESTIGATIONS
Elevated blood ornithine levels.
Genetic testing confirms diagnosis.
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