Ophthalmology: Basic eye examination

Ophthalmology: Basic eye examination

External eye and anterior segment

Ophthalmic examination requires a basic knowledge of the anatomy of the eyelids and front of the eye. You should perform direct observation unaided, with a loup and torch, or with an ophthalmoscope, followed by slit lamp examination.

Aims

  • Anatomy of the external eye and anterior segment.
  • Examination.

Anatomy

The external eye includes the eyelids, lashes, lacrimal puncta, caruncle, plica semilunaris, corneal epithelium and conjunctiva.

The anterior segment includes the cornea, iris, anterior chamber angle and lens.

Systematic examination

This should be undertaken in the following order.

Lids

  • Observe the upper eyelids for symmetry. If asymmetrical, decide which lid is ptotic (drooping) or whether the other lid is retracted.
  • Observe the lid position relative to the pupil and cornea.
  • A ptotic lid will cover more cornea and may partially or totally obscure the pupil.
  • A retracted lid will cover little or no cornea, with the sclera visible above the cornea (upper scleral show).
  • Observe the lower eyelid position for entropion (lid turning inwards) or ectropion (lid everted outwards).
  • Look for evidence of inflammation (e.g. erythema or oedema).
  • Note any lid lesions present.
  • Observe the eyelashes—any missing? Are they growing in the correct direction or in-growing (trichiasis)?
  • When appropriate, evert the eyelid.

Conjunctiva

  • Use the slit lamp at low (10×) magnification, a pen torch or an ophthalmoscope set at +12D held close to the eye or set to zero and held further away.
  • Colour:
    ○ Red. Is there injection (i.e. redness?). Does it involve the entire conjunctival surface, a segment of conjunctiva or just the area where the conjunctiva meets the cornea (circumciliary)?
    ○ Bluish or purple circumciliary injection suggests anterior uveitis.
    ○ In chemical burns, patches of ischaemia appear white, surrounded by severe congestion.
    ○ Yellow. Patients with jaundice may have a yellow tinge to their conjunctiva (icterus).
  • Appearance and texture of the conjunctiva:
    ○ Are there tarsal conjunctival follicles or papillae? These are pinkish or fine red velvety lumps.
    ○ Does the patient have chemosis (conjunctiva has an oedematous jelly-like appearance)?

Cornea

  • Is the cornea clear, or are opacities present?
  • If there is a corneal irregularity or opacity, instil a drop of fluorescein into the conjunctival sac and note any fluorescein uptake (i.e. staining), which indicates a break in the epithelium. A blue torch light is best.
  • Are there abnormal vessels (neovascularization) growing into the cornea? It should be avascular.

Intraocular pressure (IOP)

For eye pressure measurement.

Anterior chamber (AC)

Information about the AC is best obtained with the slit lamp. The direct ophthalmoscope (set at +10D) or a pen torch and loup will provide useful but limited information.

  • Is the AC quiet (i.e. is the aqueous clear)? A slit lamp will show the presence of cells and keratoprecipitates (KPs) (condensation of cells on the inner surface of the cornea).
  • Is there a hyphaema (accumulation of blood in the AC)? This may result from trauma, spontaneously ruptured iris new vessels (rubeosis iridis) with a central retinal vein occlusion, longstanding glaucoma or diabetic retinopathy, or in patients with intraocular tumours.
  • Is there a hypopyon (accumulation of white blood cells in the AC)? This may be seen in uveitis, in infective endophthalmitis, with a corneal abscess and as a manifestation of leukaemia or lymphoma.

Iris

Use the slit lamp, the ophthalmoscope at +8D or the pen torch and loup.

  • Notice the colour of each iris. Different colour irides (‘iris heterochromia’) may be associated with iritis or congenital Horner’s syndrome.
  • Identify iris lesions: iris melanoma, Lisch nodules in neurofibromatosis or abnormal iris vessels (rubeosis irides), which may signify an underlying ocular tumour, central retinal vein occlusion or diabetes.
  • Notice iatrogenic iris changes (e.g. peripheral iridectomy).

Lens

The slit lamp or direct ophthalmoscope is best to examine the lens.

  • Use the direct ophthalmoscope set at 0, and stand at arm’s length from the patient, directing the beam of light to the pupil to assess the red reflex. Lens opacities are seen as specs in the red reflex.
  • Next, move closer to the patient, at the same time increasing the magnification (usually to +6) until the lens is in focus.
  • Detect a dislocated lens with the pupil dilated. It may be caused by trauma or may indicate an underlying hereditary systemic disorder such as Marfan’s syndrome or homocystinuria.

Posterior segment and retina

The ophthalmologist is skilful in examining the fundus. You too should learn the posterior segment anatomy and be able to confidently use a direct ophthalmoscope, even without a dilated pupil.

Aims

  • Define the fundus.
  • Understand how to use an ophthalmoscope to examine the fundus.
  • Attempt the use of (i) an indirect ophthalmoscope, and (ii) a slit lamp plus special lenses.

Direct ophthalmoscopy is an essential skill since retinal examination is widely used in general practice and hospital medicine.

Definitions

  • Fundus: the retina, including the macula, blood vessels and optic nerve head.
  • Posterior segment: the area behind the lens, including the posterior chamber, vitreous, retina, choroid and optic disc.
  • Fundoscopy: examination of the fundus.
  • Posterior pole: the posterior retina, including the optic nerve head, macula and retinal blood vessels.
  • Periphery or peripheral fundus: the retina from the equator out towards the pars plana.

Examination technique

Equipment needed to examine posterior segment:

  • Direct ophthalmoscope: monocular.
  • Indirect ophthalmoscope: binocular; with a 20D lens.
  • Slit lamp biomicroscope: binocular; with or without a +90D or +78D lens.

Dilate the pupils for a better view

  • The fundus can be examined with the pupil un-dilated (best in darkness to ensure maximum pupil size). A better view is achieved if the pupils are dilated.
  • In adults, Guttae (g) tropicamide 1% is used. Phenylephrine hydrochloride (G 55) 2.5% or 10% can be given for greater dilation, especially with brown irides.

Do not dilate the pupils in the following situations

  • When responses are being monitored for neuro-observation (such as to assess a relative afferent pupillary defect).
  • When there is a risk of precipitating angle-closure glaucoma (i.e. individuals with shallow anterior angles).

Direct ophthalmoscopy

The light source is focussed by a series of mini-lenses and directed via a mirror into the patient’s eye. The observer views the illuminated retina through a sight hole in the mirror. The disc of rotating lenses can be rotated to compensate for both the observer’s and patient’s refractive errors—if both the observer and patient are emmetropic, then no lens (zero) is incorporated. The image produced is virtual and erect (i.e. the right way up). and it is magnified (15×) with a field of view of 6°.

Indirect ophthalmoscopy

This binocular head-mounted device with hand-held condensing lenses is used to examine the retina binocularly. It gives a wide field of view at low magnification. The image is both upside down and back to front.

Slit lamp biomicroscope

This is predominantly used by ophthalmologists for ophthalmic examination. The retinal image is both upside down and back to front.

Use of eye drops

All eye examinations involve the insertion of eye drops, the most common being fluorescein, topical anaesthetic and dilating drops.

Aims

  • Understand the indications for fluorescein, and the use of common dilating and anaesthetic drops.
  • Know how to instil eye drops correctly.
  • Be aware of the risks of dilating drops.

Definitions

  • Mydriatic: drop that causes mydriasis (pupil dilation).
  • Miotic: drop that causes miosis (pupil constriction).
  • Cycloplegia: loss of accommodation caused by blocking the parasympathetic innervation to the ciliary body.

Drops for ocular surface examination

Fluorescein

Fluorescein is an orange-brown crystalline substance and belongs to the triphenylmethane dyes. It is available as Minims drops or is dried onto paper (fluoret). It adopts its characteristic yellow-green colour after dilution. Use a cobalt blue light from a slit lamp or direct ophthalmoscope to see the typical green-yellow fluorescence.

  • Absorption spectrum: 465 and 490 nm (blue end).
  • Emission spectrum: 520 and 530 nm (green-yellow region).

Fluorescein is water-soluble and does not stain the corneal epithelium (hydrophobic). It does stain the Bowman’s membrane and stroma in an epithelial defect (e.g. dendritic ulcer).

Rose Bengal

Rose Bengal is a red soluble dye and belongs to the group of fluorine dyes. It is available as a 1% Minims preparation. It stains wherever there is insufficient protection of the preocular tear film:

  • Decreased tear components (e.g. keratoconjunctivitis sicca).
  • Abnormal surface epithelial cells (e.g. degenerating or dead cells, or mucous strands).

Rose Bengal should be used very sparingly, as it causes stinging due to its acid properties. It is advisable to instil topical anaesthetic prior to its use and warn the patient about discomfort.

Topical anaesthetic drops

Topical anaesthesia is used:

  • for ocular examination (tonometry and gonioscopy)
  • for contact lens fitting
  • to alleviate pain due to injury and to facilitate a thorough examination (e.g. for a foreign body, abrasion or ulcer)
  • in children prior to instillation of often stingy eye drops.

These drops must be used sparingly and in short courses as they potentially mask the severity of pain if the injury worsens. Prolonged use is epithelial toxic.

Mode of action: they prevent generation and conduction of nerve impulses—and they mostly belong to the amine group of compounds.

Anaesthetic drops are obtainable in Minims without preservatives or in bottles with preservatives.

Oxybuprocaine 0.4% (Benoxinate)

Well absorbed with onset of action within 60 s. One drop lasts approximately 15 min.

Tetracaine 0.5% and 1.0% (Amethocaine)

Onset within 60 s, and effect lasts 20 min. Contact dermatitis has been reported.

Proxymetacaine 0.5% (Ophthaine)

Onset within 30 s, and the effect lasts 15 min. It is less stingy than the other anaesthetic drops listed here and is therefore useful in children. Also available as a combination with fluorescein in Minims, and is useful for Goldmann contact tonometry.

Common dilating drops for fundal examination

In order to examine the fundus adequately, the pupil needs to be dilated.

Tropicamide 1%

This is a synthetic analogue of atropine. It reduces the parasympathetic innervation to both the sphincter pupillae and the ciliary body, resulting in a marked mydriatic action and weak cycloplegic action. It is used alone or in combination with phenylephrine for better dilation.

  • Maximum effect after 20–30 min.
  • Effect wears off after at least 6 h.

Phenylephrine 2.5%

This is a synthetic compound and is biochemically closely related to adrenaline; it acts as a potent sympathomimetic. It stimulates dilator pupillae and causes mydriasis. However, the dilator pupillae is a weaker muscle than the sphincter pupillae, hence the mydriatic effect of phenylephrine is less than with tropicamide. It is used in combination with tropicamide or cyclopentolate. It is useful to help maximize dilation in dark brown irides.

  • Maximum effect after 30 min.
  • Effect wears off after 5 h.
  • Phenylephrine 10% is rarely used due to systemic side effects.

Cyclopentolate 0.5% and 1%

This is a synthetic substance similar to atropine and has the advantage of being short acting and having a greater cycloplegic effect than tropicamide. It is commonly used in refraction in children to abolish accommodation.

  • Mydriasis and cycloplegia within 20–30 min.
  • Maximum cycloplegic effect lasts 45–60 min.
  • Effect wears off after 24 h.

Side effects: risk of allergic reaction and raised intraocular pressure. In a baby <3 months old, cyclopentolate 0.5% should be used. Hypersensitivity is less common than with atropine. Rare side effects: visual hallucinations, disorientation and ataxia.

In patients with darkly pigmented irides, the cyclopentolate effect may be insufficient for full cycloplegia; therefore, use atropine 1% drops. Note that atropine has a longer acting period and a higher risk of side effects.