Medicine – Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a group of inherited progressive retinal dystrophies in which photoreceptor cells gradually degenerate. The disease primarily affects the rods, with cone involvement occurring later in many patients.

The name is slightly misleading because RP is not primarily an inflammatory “retinitis.” It is better understood as an inherited degeneration of the retina.

1. Retinal Degeneration

In retinitis pigmentosa, there is progressive loss of photoreceptors together with characteristic pigmentary changes in the retina.

As retinal cells degenerate, pigment migrates into the retina and produces the classic bone-spicule pigmentation seen on fundoscopic examination.

Other typical retinal findings may include attenuation of retinal arterioles and a pale or waxy optic disc in more advanced disease.

2. Inheritance

Retinitis pigmentosa can follow several different inheritance patterns.

It may be:

Autosomal dominant.

Autosomal recessive.

X-linked.

There are also syndromic forms associated with systemic disease.

Because many different genes can cause RP, the age of onset, rate of progression, and severity can vary considerably between patients.

3. Rods Are Affected First

The disease predominantly affects rod photoreceptors in the early stages.

Rods are responsible mainly for vision in dim light and for much of the peripheral visual field.

This explains why the earliest symptoms are usually night blindness and progressive loss of peripheral vision.

4. Cone Involvement

As the disease progresses, cone photoreceptors may also become affected.

Cones are responsible for central visual acuity, colour vision, and vision in brighter light.

Late cone degeneration can therefore lead to loss of central vision, colour discrimination, and detailed visual acuity.

5. Night Blindness

Night blindness, or nyctalopia, is one of the earliest and most characteristic symptoms.

Patients may notice difficulty seeing in dimly lit environments, difficulty adapting when moving from bright light into darkness, or trouble navigating at night.

This occurs because rod function deteriorates before cone function.

6. Peripheral Visual-Field Loss

Loss of the peripheral visual field typically occurs before central vision is lost.

As peripheral retinal function progressively deteriorates, the visual field becomes increasingly constricted.

This eventually produces the characteristic “tunnel vision” pattern.

7. Tunnel Vision

Tunnel vision means that the patient retains a relatively narrow central area of vision while peripheral vision has been lost.

Patients may therefore have difficulty noticing objects approaching from the side, navigating unfamiliar spaces, or avoiding obstacles despite retaining relatively good central acuity early in the disease.

8. Central Vision

Central vision is often relatively preserved until later because the cones of the macula are affected after the peripheral rod system.

As cone degeneration progresses, however, central vision may decline significantly.

Complications such as cystoid macular oedema can further reduce central visual acuity.

9. Fundoscopic Findings

Classical fundoscopic features of retinitis pigmentosa include:

Bone-spicule retinal pigmentation.

Attenuated retinal vessels.

Waxy pallor of the optic disc.

These findings tend to become more obvious as the disease progresses.

10. Electroretinography

Electroretinography (ERG) can demonstrate reduced electrical responses from the retina.

Rod responses are typically reduced early, with cone responses becoming affected later.

ERG can therefore help support the diagnosis and assess the extent of generalized photoreceptor dysfunction.

11. Visual-Field Testing

Formal visual-field testing can demonstrate progressive peripheral field loss.

Ring scotomas may develop and subsequently enlarge until only a small central field remains.

This objective assessment is useful for monitoring progression and documenting functional impairment.

12. Associated Conditions

Some forms of retinitis pigmentosa occur as part of broader inherited syndromes.

An important example is Usher syndrome, in which RP is associated with sensorineural hearing loss.

Other syndromic associations can involve neurological, metabolic, renal, or skeletal abnormalities depending on the underlying genetic disorder.

13. Prognosis

Retinitis pigmentosa is usually progressive, but the rate of visual loss varies enormously between individuals and genetic subtypes.

The traditional statement that most patients are registered blind by age 40 is too absolute.

Some patients develop severe visual impairment relatively early, whereas others retain useful central vision well beyond middle age.

Therefore, prognosis should be individualised according to the specific genetic diagnosis and clinical course.

14. Treatment

There is currently no single treatment that reverses all forms of retinitis pigmentosa.

Management focuses on preserving useful vision, treating complications, providing visual rehabilitation, and identifying genetically treatable subtypes.

15. Treatment of Complications

Associated problems such as cystoid macular oedema or cataract may be treatable and can improve useful vision.

Low-vision aids, mobility training, and occupational support can also make a major difference to daily function.

16. Genetic Testing and Counselling

Because RP is genetically heterogeneous, genetic testing is increasingly important.

Identifying the causative mutation can clarify inheritance, guide family counselling, refine prognosis, and determine whether the patient may be eligible for a gene-specific therapy or clinical trial.

17. Gene Therapy

Gene therapy is available for a small subset of inherited retinal dystrophies associated with particular mutations, most notably biallelic RPE65-related retinal disease.

This does not apply to all patients with retinitis pigmentosa, but it illustrates the growing importance of precise genetic diagnosis.

18. Retinitis Pigmentosa – Note Form

Definition: inherited progressive retinal degeneration affecting photoreceptors.

Early cells affected: mainly rods.

Later cells affected: cones may become involved.

Inheritance: autosomal dominant, autosomal recessive, or X-linked.

Early symptom: night blindness.

Visual field: peripheral vision is lost first.

Typical late field defect: tunnel vision.

Fundoscopy: bone-spicule pigmentation, attenuated retinal vessels, and waxy optic-disc pallor.

Central vision: usually relatively preserved until later stages.

Investigation: visual-field testing, electroretinography, retinal imaging, and genetic testing.

Syndromic association: Usher syndrome = retinitis pigmentosa + sensorineural deafness.

Prognosis: progressive but highly variable; severe visual impairment may occur early in some patients but not universally by age 40.

Treatment: manage complications, provide low-vision support, undertake genetic counselling, and consider gene-specific therapy where applicable.

Key Clinical Pattern

Remember retinitis pigmentosa as:

Rod degeneration first → night blindness → peripheral visual-field loss → tunnel vision → later cone involvement and central visual loss.

The classic examination association is:

Night blindness + tunnel vision + bone-spicule retinal pigmentation = retinitis pigmentosa.