Ophthalmology
Squint, Ocular Injury and Community Ophthalmology
Ophthalmology miscellany for MBBS and NEET-PG: extraocular movements, concomitant versus paralytic squint, chemical and penetrating eye injuries and the NPCBVI, mapped to NMC codes OP9.
MedNext Academy | 3 min read
Squint, Ocular Injury and Community Ophthalmology
Ophthalmology miscellany for MBBS and NEET-PG: extraocular movements, concomitant versus paralytic squint, chemical and penetrating eye injuries and the NPCBVI, mapped to NMC codes OP9.
This chapter gathers the topics of ocular motility, the injured eye and community ophthalmology. It teaches the examination of eye movements and the distinction of latent from manifest and concomitant from paralytic squint, the emergency management of chemical and penetrating ocular injuries, and the national blindness-control framework with its priority on cataract.
High-yield: Squint, Ocular Injury and Community Ophthalmology
- Extraocular movements are tested by asking the patient to follow a target through the cardinal positions of gaze while keeping the head still.
- The six extraocular muscles are supplied by three nerves, remembered as LR6 (lateral rectus by cranial nerve VI) and SO4 (superior oblique by cranial nerve IV), with the rest by cranial nerve III.
- Heterophoria is a latent squint controlled by fusion and revealed only on the cover test, whereas heterotropia is a manifest, constant squint.
- The cover test detects a manifest squint by the movement of the uncovered eye to take up fixation, while the cover-uncover test reveals a latent squint.
- A concomitant squint has an equal angle in all directions of gaze and no diplopia and is typically childhood-onset, while a paralytic squint varies with gaze and causes diplopia.
- A superior oblique (fourth nerve) palsy causes vertical diplopia worse on looking down, and the patient adopts a compensatory head tilt away from the affected side.
- A lateral rectus (sixth nerve) palsy causes a convergent squint with horizontal diplopia worse on looking towards the affected side.
- Uncorrected refractive error is a common cause of eye strain and headache, so refraction is essential before attributing headache to other causes.
- A chemical burn of the eye is the one ocular emergency treated before history taking, with immediate and copious irrigation, and alkali burns are more damaging than acid burns.
- A suspected open globe (penetrating) injury must not be pressed on; the eye is shielded, kept nil by mouth, given tetanus prophylaxis and systemic antibiotics, and referred urgently.
- Sympathetic ophthalmitis is a bilateral granulomatous uveitis in the uninjured eye following a penetrating injury and is a reason to consider early enucleation of a blind, injured eye.
- The National Programme for Control of Blindness and Visual Impairment aims to reduce avoidable blindness in India, with cataract the leading target.
- Cataract remains the leading cause of blindness in India, followed by refractive error, glaucoma and corneal disease.
- The World Health Organization Vision 2020 initiative targeted the elimination of avoidable blindness from cataract, trachoma, refractive error, childhood blindness and corneal disease.
Ocular emergencies at a glance
- **Chemical burn:** Irrigate immediately before anything else. Alkali burns are worse than acid burns.
- **Open globe injury:** Shield the eye, do not press, nil by mouth, tetanus cover, antibiotics, urgent referral.
- **Sympathetic ophthalmitis:** Bilateral uveitis after a penetrating injury. Consider early enucleation of a blind injured eye.
- **NPCBVI priority:** Cataract is the leading avoidable cause of blindness targeted in India.
NMC competencies in this chapter
- **OP9.1:** Examination of extraocular movements
- **OP9.2:** Heterotropia and strabismus
- **OP9.3:** Refractive error and headache
- **OP9.4:** Avoidable blindness and the NPCBVI programme
- **OP9.5:** Ocular injury stabilisation and referral
- **OP8.5:** Optic nerve and visual pathway disease
- **OP2.6:** Proptosis: assessment and causes
Frequently Asked Questions
What is the difference between heterophoria and heterotropia?
Heterophoria is a latent squint kept straight by fusion and seen only when fusion is broken on the cover test. Heterotropia is a manifest, constant squint that is present even with both eyes open.
How is a chemical eye burn managed first?
By immediate and copious irrigation with water or saline, done before history taking, because rapid dilution limits tissue damage. Alkali burns penetrate more deeply and are more serious than acid burns.
What must you not do to a penetrating eye injury?
Do not press on or manipulate the globe, as pressure can extrude intraocular contents. Shield the eye, keep the patient nil by mouth, give tetanus and antibiotic cover, and refer urgently.
What is the leading cause of blindness in India?
Cataract remains the leading cause of blindness in India, which is why it is the main target of the National Programme for Control of Blindness and Visual Impairment, followed by refractive error and glaucoma.
Continue reading
MBBSAll Ophthalmology chapters
Continue through the Ophthalmology chapter map.
Continue studying Ophthalmology
Explore clinician-written learning resources, structured revision and practice across the MedNext platform.
Open in the MedNext appSee plans