Eye disorders: Diagnostic tests

Tests to determine the presence of eye disorders include direct evaluation techniques as well as radiologic and imaging studies.

Eye disorders: Direct evaluation

Refraction, slit-lamp examination, and tonometry allow direct evaluation of various eye structures and functions.

Refraction

Focus Topic: Eye disorders

Defined as the bending of light rays by the cornea, aqueous humor, lens, and vitreous humor in the eye, refraction enables images to focus on the retina and directly affects visual acuity. This test is done routinely during a complete eye examination or whenever a patient complains of a change in vision. It defines the degree of impairment (refractive error) and determines the degree of correction required to improve visual acuity with glasses or contact lenses.

Nursing considerations

  • Explain to the patient the test is painless and safe and that it takes about 30 minutes.
  • Tell the patient he shouldn’t use any eyedrops, including prescription eyedrops, for at least 24 hours before the test.
  • Explain that eyedrops may be instilled to dilate the pupils and inhibit accommodation by the lens. Ask the patient whether he has had a hypersensitivity reaction to eyedrops, has angle-closure glaucoma, or has an intra ocular lens implant. Dilating eyedrops shouldn’t be administered to anyone with those conditions.

Slit-lamp examination

Focus Topic: Eye disorders

The slit lamp is an instrument equipped with a special lighting system and a binocular microscope. This tool allows the practitioner to visualize in detail the anterior segment of the eye, which includes the eyelids, eyelashes, conjunctiva, sclera, cornea, tear film, anterior chamber, iris, lens, and anterior portion of the vitreous humor (vitreous face). If abnormalities are noted, special devices may be attached to the slit lamp to allow more detailed investigation.

Nursing considerations

  • If the patient is wearing contact lenses, have him remove them before the test, unless the test is being performed to evaluate the fit of the contact lenses.
  • When instilling dilating drops, tell the patient that his near vision will be blurred for 40 minutes to 2 hours. Advise him to wear dark glasses in bright sunlight until his pupils return to normal diameter.
  • Don’t administer dilating eyedrops to the patient who has angleclosure glaucoma, is hypersensitive to mydriatics, or has an intraocular lens implant.

Tonometry

Focus Topic: Eye disorders

 

Eye disorders

 

Tonometry allows noninvasive measurement of intraocular pressure (IOP) to detect glaucoma, a common cause of blindness, at an early stage in the disease. In the early stages of glaucoma, increased IOP causes the eyeball to harden and become more resistant to extraocular pressure. Pneumotonometry uses a puff of air to the eye to measure pressure; applanation tonometry provides the same information by measuring the amount of force required to flatten a known corneal area.

Nursing considerations

  • Because an anesthetic is instilled before the test, tell the patient not to rub his eyes for at least 20 minutes after the test, to prevent corneal abrasion.
  • If the patient wears contact lenses, tell him not to reinsert them for at least 30 minutes after the test.
  • If the tonometer moved across the cornea during the test, tell the patient that he may feel a slight scratching sensation in the eye when the anesthetic wears off. Explain that this sensation could be the result of a corneal abrasion and should disappear within 24 hours; however, the practitioner may prescribe prophylactic antibiotic drops.

Eye disorders: Radiologic and imaging studies

Radiologic and imaging studies include fluorescein angiography, ocular ultrasonography, and orbital computed tomography (CT).

Fluorescein angiography

Focus Topic: Eye disorders

 

Eye disorders

 

Fluorescein angiography records the appearance of blood vessels inside the eye through rapid-sequence photographs of the fundus (posterior inner part of the eye).

 

Eye disorders: Picture perfect

The photographs, which are taken with a special camera, follow the I.V. injection of sodium fluorescein. This contrast medium enhances the visibility of microvascular structures of the retina and choroid, allowing evaluation of the entire retinal vascular bed, including retinal circulation.

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Nursing considerations

  • Check the patient’s history for an intraocular lens implant, glaucoma, and hypersensitivity reactions, especially reactions to contrast media and dilating eyedrops.
  • If miotic eyedrops are ordered, tell the patient with glaucoma not to use them on the day of the test.
  • Explain to the patient that eyedrops will be instilled to dilate his pupils and that a dye will be injected into his arm. Remind him to maintain his gaze position and fixation as the dye is injected. Tell him that he may briefly experience nausea and a feeling of warmth. Reassure him as necessary.
  • Observe the patient for hypersensitivity reactions to the dye, such as vomiting, dry mouth, metallic taste, sudden increased salivation, sneezing, light-headedness, fainting, and hives. Rarely, anaphylactic shock may result.
  • Remind the patient that his skin and urine will be a yellow color for 24 to 48 hours after the test and that his near vision will be blurred for up to 12 hours.

Ocular ultrasonography

Focus Topic: Eye disorders

 

Eye disorders

 

Ocular ultrasonography measures high-frequency sound waves that pass through the eye and reflect off ocular structures, providing an illustration of the eye’s structures. This method especially helps to evaluate a fundus clouded by an opaque medium such as a cataract. In such a patient, this test can identify pathologies that ophthalmoscopy can’t normally detect. The practitioner may also order this test before such surgery as cataract removal or intraocular lens implantation. Ocular ultrasonography may also be performed before such surgery as cataract removal or implantation of an intraocular lens.

Nursing considerations

  • Tell the patient that a small transducer will be placed on his closed eyelid and that the transducer will transmit high-frequency sound waves that will reflect off the structures in the eye.
  • Inform him that he may be asked to move his eyes or change his gaze during the procedure; explain that his cooperation will help to ensure accurate results.
  • After the test, remove the water-soluble jelly that was placed on the patient’s eyelids.

Orbital computed tomography

Focus Topic: Eye disorders

Orbital CT allows visualization of abnormalities that standard X-rays don’t readily show. For instance, orbital CT can delineate the size, position, and relationship of an abnormality to adjoining structures. Contrast media may be used to define ocular tissues and help confirm a suspected circulatory disorder, hemangioma, or subdural hematoma. Orbital CT does more than just evaluate orbital and adjoining structures; it also permits precise diagnosis of many intracranial lesions that affect vision.

Nursing considerations

  • If a contrast medium will be administered, withhold food and fluids from the patient for 4 hours before the test. Check his history for hypersensitivity reactions to iodine, shellfish, or radiographic dyes.
  • Tell the patient that he’ll be positioned on an X-ray table and that the head of the table will move into the scanner, which will rotate around his head and make a whirring noise.
  • If a contrast medium will be used for the procedure, tell the patient that he may feel flushed and warm and may experience a transient headache, a salty taste, and nausea or vomiting after injection of the medium. Reassure him that these reactions to the contrast medium are typical.
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