## Photoreceptor dystrophies
Retinitis pigmentosa (see dedicated chapter)

### Stargardt’s
- Most common macular dystrophy
- AR most common: ABCA4 (or ELOVL4, PROM1), which is found on chromosome 1
 - (also AD types)

- Caused by accumulation of **lipofuscin** in the RPE
- VA drops to 6/60 usually and can present in childhood
- Features
 - Beaten-bronze, mottled macula
 - Yellow-white, pisciform lesions at the RPE: more elongated than drusen
 - Bull’s eye appearance may progress to geographic atrophy
 - CNV
 - ERG: normal/subnormal photopic, normal scotopic
 - EOG: subnormal
 - FFA: **dark choroid** (masking of the background choroid by diffuse RPE abnormality

- Fundus flavimaculatus: adult-onset form, may have normal vision

### Achromatopsia

- Rod monochromatism: lack of cone function
- Complete vs incomplete forms: better VA and some preserved colour vision in incomplete form
 - Most patients have the complete form all three cone populations are deficient

- Genes: CNGA3, CNGB3, GNAT2
- Features
 - Reduced VA (6/60) and colour vision from birth
 - **Pendular nystagmus**
 - **Photophobia**
 - Normal fundus appearance: or **mild RPE changes** (which may mimic albinism, however albinism has normal cone function and colour vision), lack of foveal reflex
 - **Hyperopia**

- Tests
 - ERG: unrecordable cone responses (normal rod responses)
 - Differentiates from Leber's congenital amaurosis which shows an extinguished ERG

 - OCT: may be normal or show foveal hypoplasia

### Blue cone monochromatism
- X-linked
- Preservation of blue cone function and partial achromatopsia
- Nystagmus
- Progressive **myopia** (cp achromatopsia)
- VA typically better than 6/60
- Normal fundus initially with then progressive macular atrophic changes
- Protan and deutan defects on colour testing
- Reduced cone response on ERG

### Congenital stationary night blindness

- Disorders causing infantile **nyctalopia**
- Non-progressive
- Normal fundus appearance
 - Types 1 (complete) and 2 (incomplete)

- Abnormal fundus appearance (aka Oguchi disease)
 - Golden yellow colour to fundus in light-adapted state (normalises after prolonged dark adaptation -Mizuo phenomenon)

- ERG: absent bipolar function (reduced b-wave)

## Macular dystrophies

### Best vitelliform macular dystrophy
- Early-onset/juvenile macular dystrophy
- Second most common macular dystrophy after Stargardt’s
- BEST1 gene: autosomal dominant
- Late in course, vision deteriorates due to CNV, scarring of GA
- Features
 - Pre-vitelliform stage: Reduced EOG (Arden index &lt;1.5) in asymptomatic child
 - Vitelliform stage: Well-defined ‘yolk-like’ lesion at the macula (vision may be unaffected at this stage)
 - Vitelliruptive: lesion breaks up and vision drops
 - Pseudohypopyon: lesion regression (often in puberty)
 - Atrophic stage: pigment disappearance leaving atrophic RPE

### Adult Foveolar Vitelliform Dystrophy
- Essentially an adult-onset Bests
- Autosomal dominant mutations in PRPH2 or BEST2 genes
- Onset is between 30-50 years old
- Features
 - Mild visual loss
 - Yellow foveal deposits at the RPE level
 - Does not affect peripheral vision or cause nyctalopia

### Sorsby macular dystrophy
- Autosomal dominant mutation of TIMP3
- Bilateral yellow-grey drusen-like lesions at the macula at Bruch’s
- Progress to subfoveal disciform CNV which may extend peripherally (unlike ARMD)
- Managed with anti-VEGF

## Choroidal dystrophies

### Gyrate atrophy
- **Autosomal recessive**: OAT gene mutation (chromosome 10)
- Elevated plasma **ornithine**: toxic to the retina and choroid

- Features
 - Gyrate retinal lesions: paving-stone areas of atrophy coalescing with scalloped borders between normal and abnormal RPE
 - Generalised **hyperpigmentation** of the residual RPE distinguishes from choroideremia
 - **Posterior** subcapsular cataracts
 - High myopia with astigmatism
 - Hyperornithinaemia
 - Normal visual acuity until approximately age 10
 - Nyctalopia

- Management: dietary restriction of arginine and vitamin B6 supplementation (pyridoxine) +/- proline supplementation

### Choroideremia

- May appear similar to gyrate atrophy
- **X-linked recessive** therefore causes visual loss in males. **CHM** gene (gene deletion also associated with deafness and learning disability)
- Female carriers show fine RPE atrophy
- Features
 - Nyctalopia
 - Field loss
 - Variable loss of VA from middle age
 - Patchy RPE and choroidal atrophy sparing the retinal vessels and optic disc
 - Posterior subcapsular cataract
 - Early vitreous degeneration
 - Reduced ERG (rods first then cones)

## Miscellaneous

### Cancer associated retinopathy
- Paraneoplastic syndrome
- Associated with an auto-antibody to a 23kD retinal photoreceptor protein: **recoverin**
- **Melanoma associated retinopathy** has been found to be associated with auto-antibodies to TRPM1 cation channels on bipolar cells
 - Presents acutely/subacutely with
 - Reduced vision
 - Nyctalopia
 - Photopsias
 - Vitelliform lesions may be seen but anterior/posterior segments may be unremarkable
 - Mild vitritis

 - VF: central, cecocentral, paracentral scotomas
 - OCT: attenuation of the parafoveal ellipsoid zone (IS/OS junction), indicative of degeneration of photoreceptors
 - ERG: attenuation of the b-wave (compared to a-wave) “electronegative response”
 - (this indicates loss of the **bipolar cell** response -b wave- with preservation of the photoreceptor response -a wave)

- NB: MAR affects rod function while CAR affects both rods and cones (cones moreso)

### Incontinentia pigmenti

- X-linked **dominant** genodermatosis (neurocutaneous disorder)
- Lethal in males
- Cutaneous stages
 - Vesicular (1-2 weeks)
 - Verrucous (2-6 weeks)
 - Hyperpigmented (3-6 months)
 - Hypopigmented (2-3rd decade)

- Skin findings: bullae on extremities, hyperpigmented macules on trunk, alopecia, eyelash hypogenesis
- Brain abnormalities: microcephaly, seizures, LD
- Ocular findings (20-35%): **ROP-like signs** including incomplete peripheral retinal vascularisation leading to neovascular membranes, vitreous hemorrhage and tractional RD
 - Strabismus
 - Cataracts
 - Optic atrophy
 - Microphthalmos

- Dental: partial anodontia, delayed dentition, impactions
- Skeletal: scoliosis, spina bifida, congenital hip dislocation

### Susac syndrome

- Microangiopathy of brain retina and cochlea, triad of:
 - Encephalopathy: migraine-like headaches, ataxia, vertigo, sensory disturbance
 - BRAO
 - Sensorineural hearing loss: typically permanent
 - \*these may not present concurrently\*

- Presumed autoimmune epitheliopathy causing microinfarcts
- F>M, presenting between 20 and 40 years old
- Tests:
 - MRI: supratentorial white matter lesions eg. ‘snowball lesion’ in corpus callosum
 - FFA: ‘Gass plaques’ ie yellowish-white retinal wall plaques
 - Audiogram
 - OCT

- Management: early, aggressive immunosuppression
 - High dose glucocorticoids
 - Cyclophosphamide
 - Rituximab
 - IVIG/plasmapheresis

### Bietti’s crystalline dystrophy

- Autosomal recessive mutation of CYP4V2
- Chorioretinal dystrophy: multiple small intraretinal crystalline deposits
 - Also found in cornea and lymphocytes
 - Crystals composed of cholesterol and lipid

- More common in East Asia
- RPE and choroidal atrophy: moth-eaten appearance of FFA
- Night blindness
- Progressive field loss
- Abnormal ERG and EOG

### Angioid streaks

- Breaks in Bruch’s membrane which is also thickened
- Systemic associations ("**PEPSI**" mneumonic)
 - Pseudoexanthoma elasticum
 - Ehlers-Danlos
 - Paget’s disease
 - Sickle cell
 - Idiopathic
 - Beta thalassaemia

- Features
 - Irregular red-brown lines radiating from optic nerve to periphery
 - CNV
 - Peripapillary atrophy
 - Optic nerve head drusen
 - Optic atrophy
 - FFA: hyperfluorescence early with late staining

- Complications
 - Choroidal rupture after minor trauma: avoid contact sports
 - CNV

- Management
 - Avoid contact sports
 - anti-VEGF for subfoveal CNV

### White without pressure

- Typically affects asians and afro-caribbeans
- Presents as white sheen of retina skin to during normal scleral indentation
- Absent choroidal markings
- May mimic shallow retinal detachments

### Summarised medical retinopathies

<table>
 <thead>
 <tr>
 <th>Name</th>
 <th>Genetics</th>
 <th>Findings</th>
 <th>Tests</th>
 </tr>
 </thead>
 <tbody>
 <tr>
 <td>Stargardt’s</td>
 <td>AR ABCA4</td>
 <td>Pisciform yellow-white flecks, bull’s eye atrophy, ‘beaten-bronze’ atrophy</td>
 <td>FFA: dark choroid ERG: macular dysfunction</td>
 </tr>
 <tr>
 <td>Congenital stationary night blindness</td>
 <td>AD, AR, XL Normal fundi vs abnormal (Oguchi’s) Complete vs incomplete</td>
 <td>Golden yellow sheen to fundus in Oguchis</td>
 <td>ERG: reduced/undetectable rod ERG, negative bright flash response</td>
 </tr>
 <tr>
 <td>Best’s</td>
 <td>AD BEST1</td>
 <td>Retain good vision Yolk-like lesion at posterior pole (eventually breaks down to mottled geographic atrophy)</td>
 <td>EOG: reduced Arden ratio ERG: normal</td>
 </tr>
 <tr>
 <td>Gyrate atrophy</td>
 <td>AR OAT gene</td>
 <td>RPE/choroidal atrophy, scalloped appearance, enlarging</td>
 <td>Reduced ERG (rod&gt;cone) Elevated plasma ornithine</td>
 </tr>
 <tr>
 <td>Choroideremia</td>
 <td>XL CHM gene</td>
 <td>Fine RPE atrophy, granular pigment in mid-periphery, sparing vessels/disc</td>
 <td>Reduced ERG (rod&gt;cone)</td>
 </tr>
 <tr>
 <td>Lebers congenital amaurosis</td>
 <td>&gt;25 genes A subtype of RP RPE65 GUCY2D</td>
 <td>Congenital blindness, pendular, roving nystagmus, hypermetropia. Normal fundus Eye poking (oculo-digital sign) Keratoconus</td>
 <td>Extinguished ERG</td>
 </tr>
 <tr>
 <td>Achromatopsia</td>
 <td>AR Lack of cone function</td>
 <td>Pendular nystagmus Hypermetropia Roving eye movements Photophobia</td>
 <td>Absent cone ERG Normal rod ERG</td>
 </tr>
 <tr>
 <td>X-linked retinoschisis</td>
 <td>X-linked RS1</td>
 <td>Foveal schisis, spoke-wheel, hyperopia</td>
 <td></td>
 </tr>
 </tbody>
</table>

Photoreceptor dystrophies Retinitis pigmentosa (see dedicated chapter) Stargardt’s Most common macular dystrophy AR most common: ABCA4 (or ELOVL4, PROM1),…

Medical Retina

Miscellaneous Retinopathies

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