Ophthalmology
Retina and Optic Nerve
Retina for MBBS and NEET-PG: CRAO and CRVO, diabetic and hypertensive retinopathy, retinal detachment, macular degeneration, papilloedema and optic neuritis, mapped to NMC codes OP8.
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Retina and Optic Nerve
Retina for MBBS and NEET-PG: CRAO and CRVO, diabetic and hypertensive retinopathy, retinal detachment, macular degeneration, papilloedema and optic neuritis, mapped to NMC codes OP8.
This chapter covers the posterior segment and the optic nerve, the seat of many blinding diseases. It teaches the recognition of the vascular occlusions, diabetic and hypertensive retinopathy, retinal detachment and macular degeneration, the systematic technique of fundus examination, and the optic nerve signs such as the relative afferent pupillary defect and papilloedema.
High-yield: Retina and Optic Nerve
- Central retinal artery occlusion causes sudden, painless, profound loss of vision with a pale retina and a cherry-red spot at the fovea, and it is an ocular emergency.
- Central retinal vein occlusion causes sudden painless visual loss with widespread flame haemorrhages, dilated tortuous veins and a stormy sunset fundus.
- Diabetic retinopathy is classified as non-proliferative, with microaneurysms, dot-and-blot haemorrhages and hard exudates, and proliferative, with new vessels.
- The commonest cause of visual loss in diabetic retinopathy is diabetic macular oedema.
- Pan-retinal photocoagulation is the treatment for proliferative diabetic retinopathy, ablating ischaemic peripheral retina to regress new vessels.
- Hypertensive retinopathy shows arteriolar narrowing, arteriovenous nicking, flame haemorrhages, cotton-wool spots and, in malignant hypertension, papilloedema.
- Rhegmatogenous retinal detachment follows a retinal break and presents with flashes, floaters and a curtain descending across the field.
- Age-related macular degeneration is the leading cause of blindness in the elderly in developed countries; the wet form is treated with intravitreal anti-VEGF injections.
- Retinitis pigmentosa causes night blindness with a ring scotoma, bone-spicule pigmentation, attenuated vessels and a waxy pale disc.
- A relative afferent pupillary defect on the swinging torch test indicates an optic nerve or extensive retinal lesion.
- Papilloedema is bilateral optic disc swelling from raised intracranial pressure and characteristically preserves visual acuity until late.
- Optic neuritis causes acute painful visual loss with colour desaturation and a relative afferent pupillary defect and is often associated with multiple sclerosis.
- Retinopathy of prematurity affects low-birthweight infants exposed to oxygen and requires screening, as it can lead to retinal detachment and blindness.
- The red reflex is checked first at fundoscopy, and its absence (leucocoria) in a child raises the possibility of retinoblastoma or a congenital cataract.
Sudden painless visual loss
- **CRAO:** Pale retina, cherry-red spot at the fovea. Ocular emergency.
- **CRVO:** Widespread flame haemorrhages, dilated tortuous veins, stormy sunset fundus.
- **Vitreous haemorrhage:** Loss of the red reflex, floaters. Often from proliferative diabetic retinopathy.
- **Retinal detachment:** Flashes, floaters and a descending curtain in the field of vision.
NMC competencies in this chapter
- **OP8.1:** Retinal vascular occlusions
- **OP8.2:** Laser therapy in retinal diseases
- **OP8.3:** Fundus examination technique and findings
- **OP8.4:** Retinal disease treatment modalities
- **OP8.5:** Optic nerve and visual pathway disease
- **OP6.1:** Intraocular inflammation
- **OP9.4:** Avoidable blindness and the NPCBVI programme
Frequently Asked Questions
What causes a cherry-red spot at the macula?
In central retinal artery occlusion the inner retina becomes pale and oedematous, while the thin fovea still shows the underlying choroidal circulation, producing a cherry-red spot. It is a painless emergency.
How is diabetic retinopathy classified?
Into non-proliferative, with microaneurysms, haemorrhages and hard exudates, and proliferative, with new vessels that can bleed. Macular oedema is the commonest cause of vision loss in either stage.
What is a relative afferent pupillary defect?
It is a sign detected on the swinging torch test where the affected pupil dilates when the light swings to it, indicating an optic nerve or extensive retinal lesion.
Why does papilloedema preserve vision early?
Papilloedema is passive disc swelling from raised intracranial pressure rather than direct nerve damage, so central visual acuity is preserved until late, though the blind spot enlarges.
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