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Snellen

Traditional Snellen chart used for visual acuity testing. Illustration only; this is a scaled image and hence not suitable for vision testing.

Slit lamp Eye examination by Ophthalmologist

Slit lamp examination of the eyes in an ophthalmology clinic

An eye examination is a battery of tests performed by an ophthalmologist or optometrist assessing vision and ability to focus on 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 diseases are silent or asymptomatic.

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

Comprehensive eye examination

Case history

Entrance tests

Refraction

  • Monocular
  • Binocular balance

Functional tests

Health assessment

Setting

Ideally, the eye examination consists of an external examination, followed by specific tests for visual acuity, pupil function, extraocular muscle motility, visual fields, intraocular pressure and ophthalmoscopy through 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

GlassPerscriptionRig

Determining a prescription for eyeglasses

External examination

External examination of eyes consists of inspection of the eyelids, surrounding tissues and palpebral fissure. Palpation of the orbital rim may also be desirable, depending on the presenting signs and symptoms. The conjunctiva and sclera can be inspected by having the individual look up, and shining a light while retracting the upper or lower eyelid. The cornea and iris may 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. The terms 20/20 and 6/6 are derived from standardized sized objects that can be seen by a "person of normal vision" at the specified distance. For example, if one can see at a distance of 20 ft an object that normally can be seen at 20 ft, then one has 20/20 vision. If one can see at 20 ft what a normal person can see at 40 ft, then one has 20/40 vision. Put another way, suppose you have trouble seeing objects at a distance and you can only see out to 20 ft what a person with normal vision can see out to 200 feet, then you have 20/200 vision. The 6/6 terminology is more commonly used in Europe, and represents distances in meters.


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 (1 mm 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 mnemonic PERRLA (D+C): Pupils Equal and Regular; Reactive to Light and Accommodation (Direct and Consensual).

A swinging-flashlight test may also be desirable if neurologic damage is suspected. The swinging-flashlight test is the most useful clinical test available to a general physician for the assessment of optic nerve anomalies. 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 efferent defect 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 afferent defect 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 neuropathology is present. However, if accompanied by ptosis of 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 syphilis.

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 palsy of the cranial nerves innervating the extraocular muscles. Saccades are assessed by having the patient move his or her eye quickly to a target at the far right, left, top and bottom. This tests for saccadic dysfunction whereupon poor ability of the eyes to "jump" from one place to another may impinge on reading ability and other skills.

Slow tracking, or "pursuits" are assessed by the 'follow my finger' test, in which the examiner's finger traces an imaginary "double-H", which touches upon the eight fields of gaze. These test the inferior, superior, lateral and medial rectus muscles of the eye, as well as the superior and inferior oblique muscles.

Visual field (confrontation) testing

Main article: Visual field
Main article: Visual field test

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 count 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 humour from the eye.

Ophthalmoscopy

A red reflex can 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 retina and 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 disc and retinal arteries and veins are the main focus of examination during ophthalmoscopy. The optic disc should appear slightly oval, with a pink colour.

Slit lamp

Close inspection with a slit lamp is performed 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 ophthalmoscopy can also be performed through the slit lamp. The binocular slit-lamp examination provides stereoscopic magnified view of the eye structures in striking detail, enabling exact anatomical diagnoses to be made for a variety of eye conditions. Combined with special lenses like Goldmann 3-mirror lens, Gonioscopy single-mirror/ Zeiss 4-mirror lens for angle structures and +90D lens, +78D lens, +66D lens & Hruby (-56D) lens, the examination of retinal structures is accomplished.

Fluorescein staining before slit lamp examination may reveal corneal abrasions or herpes simplex infection.

References

See also

Conditions diagnosed during eye examinations

Main article: List of eye diseases and disorders

Other tests that may be performed during eye examinations

Miscellaneous

External Links

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