Retinitis pigmentosa post pic

Retinitis Pigmentosa (RP)

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Introduction

Retinitis pigmentosa (RP) encompasses a clinically and genetically diverse group of inherited retinal disorders that cause retinal degeneration. RP is the most common hereditary retinal dystrophy which causes progressive vision loss. In the UK, the prevalence of RP is approximately 1 in 4,000.1


Causes and Risk Factors

RP is caused by mutations in genes encoding proteins important for photoreceptor and retinal pigment epithelium (RPE) function and survival. Most cases result from mutations of the rhodopsin gene.

Genetic predisposition is the principal risk factor for RP. It may be sporadic or inherited in an autosomal dominant, autosomal recessive or X-linked pattern (Table 1).2 The prognosis is related to the mode of inheritance.

While RP is a disease usually limited to the eye, it can be associated with rare systemic syndromes (syndromic RP) with the most common being Usher syndrome (US) and Bardet-Biedl syndrome (BBS). US is the most common inherited cause of combined deafness and blindness while BBS is characterised by rod-cone dystrophy, obesity, polydactyly, learning disabilities and hypogonadism.

Table 1. Estimated percentage and prognosis of RP types.2

Type of RP % Prognosis
Sporadic 30 Good
Autosomal dominant 25 Best
Autosomal recessive 20 Poor
X-linked 15 Poorest
Syndromic RP 10 Dependent on the type of underlying syndrome

History and Examination

RP typically presents as complaints of visual disturbances, beginning in childhood or in the early teenage years. However, patients may present in their 40s as this is usually when severe visual impairment occurs. Either way, patients are first assessed by primary care physicians who then make an ophthalmology referral.

History

Presenting Complaint

Patient with suspected RP will primarily complain about not being able to see well in low-light environments or will have difficulty adapting when moving from a well-lit area to a dark area. Patients tend not to notice they have reduced peripheral vision unless the symptoms have been occurring over a prolonged period of time.

History of Presenting Complaint

Be sure to ask about the age of onset to differentiate between genetic causes of RP. If the patient is young, a collateral history might be the main source of information (i.e. parents).

Most common symptoms:

  • Reduced peripheral vision or “tunnel vision”
  • Nyctalopia (night blindness)
  • Impaired dark adaptation

Less common symptoms:

  • Photopsia (flashing lights)
  • Glare
  • Reduced central vision

*Rod photoreceptors are affected earlier and more severely than cone photoreceptors in most forms of RP, thus giving rise to the above symptoms.

Past Medical History

  • Exposure to infectious diseases such as syphilis, rubella and diffuse unilateral subacute neuroretinitis, as they can mimic the symptoms of RP.
  • Previous ocular injuries
  • Ophthalmic history

Medications and Allergies

It is important to ask about chloroquine and thioridazine hydrochloride as they can cause ocular signs similar to RP.

Family History

It is critical to determine the type of inheritance pattern by drawing a genetic pedigree for the patient’s family, as genetic inheritance is related to the prognosis of RP.

Social History

  • History of smoking
  • Alcohol consumption
  • Illicit drug use
  • Effect on driving
  • Effect on occupation

Systems Review

It is important to do a systems review to identify syndromic RP. Topics to ask about include hearing, weight, sexual history and learning disabilities.

Clinical Examination

A thorough eye and fundoscopy examination should be performed in patients with suspected retinitis pigmentosa. Please see the Geeky Medics guide here for a description of the exam.

Most common findings:

  • Typically symmetrical bilateral presentation
  • Classic triad (Figure 1):
    • Bone-spicule retinal pigmentation
    • Arteriolar attenuation
    • ‘Waxy’ optic disc pallor
  • Retinal pigment epithelium (RPE) atrophy

Less common findings:

  • Myopia
  • Cataract (posterior subcapsular subtype)
  • Optic disc drusen
  • Cystoid macular oedema (CMO)
retinitis pigmentosa
Figure 1. Right fundus photography showing the classic triad of mid-peripheral bone-spicule retinal pigmentation, arteriolar attenuation and ‘waxy’ optic disc pallor in RP.5

Differential Diagnoses

The clinical presentation of RP is similar to several other conditions that cause pigmentary retinopathy.

Genetic

  • Leber congenital amaurosis
  • Gyrate atrophy
  • Choroideremia

 Infection

  • Syphilis
  • Rubella
  • Diffuse unilateral subacute neuroretinitis

Drug toxicity

  • Chloroquine

Investigations

Bedside Investigations

  • Snellen chart (assesses visual acuity) – normal or may have myopia
  • Confrontational visual field (screens for visual field defect) – reduced peripheral vision
  • Dilated fundoscopy examination – bone-spicule retinal pigmentation, arteriolar attenuation, ‘waxy’ optic disc pallor, RPE atrophy

Specialist Investigations

  • Electroretinogram (abnormal result is essential for diagnosis) – reduction in ‘a’ and ‘b’ wave amplitudes and implicit time may be prolonged in early disease. Patients with advanced disease may have a non-detectable ERG.
  • Perimetry (formally assesses any visual field defect) – characteristic ring scotoma in the mid-periphery of the visual field
  • Genetic testing – rhodopsin gene mutation, or other mutations

Imaging

  • Optical coherence tomography – may detect CMO

Management

Conservative

Conservative management involves supportive measures to optimise vision:

  • Low vision aid (e.g. glasses, magnifiers)
  • Visual rehabilitation
  • Sunglasses (limits UV exposure)

Follow-up involves:

  • An annual follow-up to detect treatable vision-threatening complications and provide support.

Medical

Medical management involves treating RP associated complications:

  • Carbonic anhydrase inhibitors for CMO.4
  • Topical dorzolamide or brinzolamide initially.
  • Oral acetazolamide if no improvement.

Surgical

Surgical management involves treating RP associated complications:

  • Cataract surgery

Complications

Complications of RP include:

  • Cataract
  • CMO

Prognosis

  • RP is not curable at the moment
  • Treatments are only modestly effective in slowing down retinal degeneration
  • Patients tend to lose 50% of their remaining visual field every 5 years4
  • Complete visual loss is rare

Key Points

  • RP is the most common hereditary retinal dystrophy, resulting in retinal degeneration and progressive vision loss.
  • Most cases result from sporadic mutations of the rhodopsin gene.
  • The most common symptoms include reduced peripheral and night vision.
  • The most common clinical findings include the classic clinical triad of bone-spicule retinal pigmentary changes, arteriolar attenuation and ‘waxy’ disc pallor.
  • Conservative management involves the use of low vision aid, visual rehabilitation and sunglasses.
  • Medical management involves the administration of oral or topical carbonic anhydrase inhibitors for secondary CMO.
  • Surgical management involves cataract surgery for secondary cataract.
  • Complications of non-managed RP can include cataract and CMO.

References

  1. Fight for Sight. Retinitis pigmentosa. Published in 2019. [LINK]
  2. Ferrari et al. Retinitis pigmentosa: genes and disease mechanisms. Published in 2011. [LINK]
  3. Denniston AKO, Murray PI. Oxford Handbook of Ophthalmology. Published in 2018.
  4. Grover S, Fishman GA, Anderson RJ et al. Rate of visual field loss in retinitis pigmentosa. Published in 1997. [LINK]
  5. Image kindly provided by Dr Peng Yong Sim, Ophthalmology Registrar.

Reviewer

Dr Peng Yong Sim

Ophthalmology Registrar (ST2)


Editor

Hannah Thomas


 

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