Indirect Ophthalmoscopy (Binocular Indirect Ophthalmoscopy - BIO)

Principle

Advantages Over Direct Ophthalmoscopy

Condensing Lenses

Technique

1. Patient position: Supine on a bed or reclining chair (not sitting upright).
2. Pupil dilation: Mandatory. Reducing ambient light improves contrast and reduces required light intensity.
3. Eyepiece setup: Set interpupillary distance correctly; centre the light beam in the viewing frame.
4. Patient instruction: Keep both eyes open at all times. Gently separate lids if needed.
5. Lens handling: Hold the condensing lens with the flat surface facing the patient.
6. Examination order: Examine the peripheral fundus first - this allows the patient to adapt to the light. Ask the patient to move the eyes to optimal positions for each quadrant.
7. Children: A speculum may be needed to keep lids apart; a squint hook can help direct globe position (e.g. for ROP screening).

Scleral Indentation (Depression)

• Improve visualization of the retina anterior to the equator (the peripheral retina not otherwise visible)
• Allow kinetic evaluation of retinal breaks and lesions

• Should only be attempted after mastering the basic BIO technique.
• Requires coordination between the indenter position and the viewing apparatus.
• A cotton-tipped applicator is preferred by some practitioners.
• The indenter must be kept tangential to the globe at all times - perpendicular pressure causes pain and risks perforation if the sclera is thin.

1. Ask patient to look down.
2. Apply the scleral indenter to the outside of the upper eyelid at the tarsal plate margin.
3. Ask the patient to look up while advancing the indenter parallel to the globe.
4. Align your eyes with the condensing lens and indenter.
5. Exert gentle pressure to create a mound, then sweep to adjacent areas.

Fundus Drawing

Clinical Uses

• Retinal detachment - detection and mapping of retinal breaks
• Retinopathy of Prematurity (ROP) screening in neonates
• Peripheral retinal examination (lattice degeneration, tears, dialysis)
• Trauma - detecting peripheral breaks or detachment after blunt eye injury (with scleral depression ~1 month post-trauma)
• Tumour evaluation (uveal melanoma, choroidal lesions)
• Vitreous haemorrhage - BIO penetrates media opacity better than slit lamp biomicroscopy
• Paediatric fundus examination

Lacrimal Flow

Anatomy of the Lacrimal Drainage System

1. Puncta

• Located at the posterior edge of the lid margin, at the junction of the lash-bearing lateral 5/6 (pars ciliaris) and the medial non-ciliated 1/6 (pars lacrimalis)
• The punctum and vertical canaliculus are part of the tarsal plate
• Normally face slightly posteriorly - can be inspected by everting the medial lid

2. Canaliculi

• Each canaliculus passes vertically ~2 mm from the lid margin (this short vertical segment = ampulla)
• Then turns medially and runs horizontally ~8 mm to reach the lacrimal sac
• The horizontal canaliculus is surrounded by the palpebral part of orbicularis oculi (Horner muscle)
• The superior and inferior canaliculi unite (>90% of cases) to form the common canaliculus, which opens into the lateral wall of the lacrimal sac
• A small mucosal flap - the valve of Rosenmüller - overhangs the junction of the common canaliculus and lacrimal sac (the internal punctum), preventing reflux of tears back into the canaliculi

3. Lacrimal Sac

• 10-12 mm long, lies in the lacrimal fossa between the anterior and posterior lacrimal crests
• Separated from the middle meatus of the nasal cavity by the lacrimal bone and frontal process of the maxilla
• In dacryocystorhinostomy (DCR), an anastomosis is created between the sac and nasal mucosa to bypass nasolacrimal duct obstruction

4. Nasolacrimal Duct

• 12-18 mm long, the inferior continuation of the lacrimal sac
• Descends and angles slightly laterally and posteriorly
• Opens into the inferior nasal meatus, lateral to and below the inferior turbinate
• The opening is partially covered by a mucosal fold - the valve of Hasner

Physiology of Tear Flow

Step 1 - Surface flow (Fig. 3.2A)

Step 2 - Blink (Fig. 3.2B)

• Compresses the ampullae
• Shortens and compresses the horizontal canaliculi
• Closes and moves the puncta medially, resisting reflux

Step 3 - Eye opening (Fig. 3.2C)

Summary of Tear Flow Path

Lacrimal gland
      ↓
Ocular surface (across conjunctiva and cornea)
      ↓
Marginal tear strips (upper and lower lids)
      ↓
Lacus lacrimalis (medial canthus)
      ↓
Puncta (upper & lower, ~2 mm vertical ampulla)
      ↓
Horizontal canaliculi (~8 mm each)
      ↓
Common canaliculus → Valve of Rosenmüller
      ↓
Lacrimal sac (10-12 mm) - in lacrimal fossa
      ↓
Nasolacrimal duct (12-18 mm) → Valve of Hasner
      ↓
Inferior nasal meatus

Key Valves

Clinical Relevance - Epiphora (Watering Eye)

1. Hypersecretion - secondary to anterior segment disease (dry eye causing paradoxical reflex tearing, inflammation). Treatment is usually medical.
2. Defective drainage - compromised lacrimal drainage system (punctal stenosis, canalicular obstruction, NLD obstruction, dacryocystitis). Treatment often requires surgical intervention.

Clinical tip: A watering eye is commonly caused by reflex hypersecretion secondary to a dry ocular surface - treat the dryness first before assuming a drainage problem.