Eye examination

Image:Snellen06.png An eye examination is a battery of tests performed by an ophthalmologistor optometristassessing visionand ability to focuson and discern objects, as well as other tests and examinations pertaining to the eyes. All people should have periodic and thorough eye examinations as part of routine care by the primary care physician, especially since many eye diseasesare silent or asymptomatic.

Eye examinations may detect potentially treatable blindingeye diseases, ocular manifestations of systemic disease, or signs of tumoursor other anomalies of the brain.

Comprehensive eye examination

Case history

Entrance tests

• External examination
• Visual acuity
• Amplitude of accommodation
• Color vision
• Cover test
• Stereopsis
• Near point of convergence
• Extraocular motilities
• Pupils
• Visual field screening
• Interpupillary distance

Refraction

• Lensometry
• Keratometry
• Retinoscopy
• Refraction

• Monocular
• Binocular balance

• Cycloplegicrefraction

Functional tests

• Accommodativesystem

• Negative relative accommodation
• Positive relative accommodation

• Vergencesystem

Health assessment

• Slit lampbiomicroscopy
• Direct ophthalmoscopy
• Binocular indirect ophthalmoscopy
• Tonometry

• Goldmann applanation tonometry
• Non-contact tonometry

• Amsler grid
• Tangent screen
• Gonioscopy

Setting

Ideally, the eye examination consists of an external examination, followed by specific tests for visual acuity, pupilfunction, extraocular musclemotility, visual fields, intraocular pressureand ophthalmoscopythrough a dilated pupil.

A minimal eye examination consists of tests for visual acuity, pupil function, and extraocular muscle motility, as well as direct ophthalmoscopy through an undilated pupil.

Basic examination

External examination

External examination of eyes consists of inspection of the eyelids, surrounding tissuesand palpebral fissure. Palpation of the orbital rimmay also be desirable, depending on the presenting signs and symptoms. The conjunctivaand scleracan be inspected by having the individual look up, and shining a light while retracting the upper or lower eyelid. The corneaand irismay be similarly inspected.

Visual acuity

Main article: Visual acuity

Visual acuity is the eye's ability to detect fine details and is the quantitative measure of the eye's ability to see an in-focus image at a certain distance. The standard definition of normal visual acuity (20/20 or 6/6 vision) is the ability to resolve a spatial pattern separated by a visual angle of one minute of arc. This is often measured with a Snellen chart.

Pupil function

Main article: Pupil

An examination of pupilary function includes inspecting the pupils for equal size (1mm or less of difference may be normal), regular shape, reactivity to light, and direct and consensual accommodation. These steps can be easily remembered with the mnemonicPERRLA (D+C): Pupils Equal and Regular; Reactive to Light; Accommodate (Direct and Consensual).

A swinging-flashlight testmay also be desirable if neurologicdamage is suspected. The swinging-flashlight test is the most useful clinical test available to a general physicianfor the assessment of optic nerveanomalies. This test detects the afferent pupil defect, also referred to as the Marcus Gunn pupil. In a normal reaction to the swinging-flashlight test, both pupils constrict when one is exposed to light. As the light is being moved from one eye to another, both eyes begin to dilate, but constrict again when light has reached the other eye.

If there is an efferentdefect in the left eye, the left pupil will remain dilated regardless of where the light is shining, while the right pupil will respond normally. If there is an afferentdefect in the left eye, both pupils will dilate when the light is shining on the left eye, but both will constrict when it is shining on the right eye.

If there is a unilateral small pupil with normal reactivity to light, it is unlikely that a neuropathologyis present. However, if accompanied by ptosisof the upper eyelid, this may indicate Horner's syndrome.

If there is a small, irregular pupil that constricts poorly to light, but normally to accommodation, this is an Argyll Robertson pupil, which is a sign of tertiary syphillis.

Ocular motility

Main article: Extraocular muscles

Ocular motility should always be tested, especially when patients complain of double vision or physicians suspect neurologic disease. First, the doctor should visually assess the eyes for deviations that could result from strabismus, extraocular muscle dysfunction, or oculomotor nerve dysfunction. Saccadesare assessed by having the patient move his or her eye quickly to a target at the far right, left, top and bottom.

Slow tracking is assessed by the 'follow my finger' test, in which the examiner's finger traces an imaginary "H", which touches upon the six cardinal fields of gaze. These test the inferior, superior, lateraland medialrectus musclesof the eye, as well as the superiorand inferioroblique muscles.

Visual field (confrontation) testing

Main article: Visual field

Evaluation of the visual fields should never be omitted from the basic eye examination. Testing the visual fields consists of confrontation field testing in which each eye is tested separately to assess the extent of the peripheral field. To perform the test, the individual occludes one eye while fixated on the examiner's eye with the non-occluded eye. The patient is then asked to counts the number of fingers that are briefly flashed in each of the four quadrants. This method is preferred to the wiggly finger test that was historically used because it represents a rapid and efficient way of answering the same question: is the peripheral visual field affected?

Common problems of the visual field include scotoma(area of reduced vision), hemianopia(half of visual field lost), homonymous quadrantanopia(involving both eyes) and bitemporal hemianopia.

Intraocular pressure

Intraocular pressure can be measured by any of a series of devices designed to measure the outflow (and resistance to outflow) of the aqueous humourfrom the eye.

Ophthalmoscopy

A red reflexcan be seen when looking at a patient's pupil through a direct ophthalmoscope. This part of the examination is done from a distance of about 50 cm. The actual colour varies with the patient's complexion, but should be symmetrical between the two eyes. An opacity may indicate a cataract.

Ophthalmoscopy allows the physician to look directly at the retinaand other tissue at the back of the eye. This is best done after the pupil has been dilated with eye drops. A limited view can be obtained through an undilated pupil, in which case best results are obtained with the room darkened and the patient looking towards the far corner.

The optic discand retinal arteriesand veinsare the main focus of examination during ophthalmoscopy. The optic disc should appear slightly oval, with a pinkcolour.

Slit lamp

Close inspection with a slit lampis performed by ophthalmologists to detect eye diseases. A small vertical beam of light is run over the eye horizontally. It allows inspection of all the media, from cornea to vitreous, and ophthalmoscopycan also be performed through the slit lamp.

Fluoresceinstaining before slit lamp examination may reveal corneal abrasionsor herpes simplexinfection.

References

• eMedicine article on Neuro-ophthalmic examination

See also

• Electrooculography
• Electroretinography

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Eye+examination Wikipedia article Eye examination.