pachymetry

pachymetry

(pă-kĭm′ĕ-trē)
Measurement of the thickness of a body part, esp. the thickness of the cornea.

Pachymetry

Synonym/acronym: N/A.

Common use

To assess the thickness of the cornea prior to LASIK surgery and evaluate glaucoma risk.

Area of application

Eyes.

Contrast

N/A.

Description

Pachymetry is the measurement of the thickness of the cornea using an ultrasound device called a pachymeter. Refractive surgery procedures such as LASIK (laser-assisted in-situ keratomileusis) remove tissue from the cornea. Pachymetry is used to ensure that enough central corneal tissue remains after surgery to prevent ectasia, or abnormal bowing, of thin corneas. Also, studies point to a correlation between increased risk of glaucoma and decreased corneal thickness. This correlation has influenced some health-care providers (HCPs) to include pachymetry as a part of a regular eye health examination for patients who have a family history of glaucoma or who are part of a high-risk population. African Americans have a higher incidence of glaucoma than any other ethnic group.

This procedure is contraindicated for

    N/A

Indications

  • Assist in the diagnosis of glaucoma (Note: the intraocular pressure in glaucoma patients with a thin cornea, 530 micron or less, may be higher than in patients whose corneal thickness is within normal limits)
  • Determine corneal thickness in potential refractive surgery candidates
  • Monitor the effects of various therapies using eye drops, laser, or filtering surgery

Potential diagnosis

Normal findings

  • Normal corneal thickness of 535 to 555 micron

Abnormal findings related to

  • Bullous keratopathy
  • Corneal rejection after penetrating keratoplasty
  • Fuchs’ endothelial dystrophy
  • Glaucoma

Critical findings

    N/A

Interfering factors

  • Factors that may impair the results of the examination

    • Inability of the patient to cooperate or remain still during the test because of age, significant pain, or mental status.
    • Improper technique during application of the probe tip to the cornea.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this procedure can assist in measuring the thickness of the cornea in the eye.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of narrow-angle glaucoma. Obtain a history of known or suspected visual impairment, changes in visual acuity, and use of glasses or contact lenses.
  • Obtain a history of the patient’s known or suspected vision loss, including type and cause; eye conditions with treatment regimens; eye surgery; and other tests and procedures to assess and diagnose visual deficit.
  • Obtain a history of symptoms and results of previously performed laboratory tests, diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Instruct the patient to remove contact lenses or glasses, as appropriate. Instruct the patient regarding the importance of keeping the eyes open for the test.
  • Review the procedure with the patient. Explain that the patient will be requested to fixate the eyes during the procedure. Address concerns about pain and explain that no pain will be experienced during the test, but there may be moments of discomfort. Explain that some discomfort may be experienced after the test when the numbness wears off from anesthetic drops administered prior to the test, or discomfort may occur if too much pressure is used during the test. Inform the patient that an HCP performs the test and that to evaluate both eyes, the test can take 3 to 5 min.
  • Sensitivity to social and cultural issues,  as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

  • Potential complications: N/A
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Instruct the patient to cooperate fully and to follow directions. Ask the patient to remain still during the procedure because movement produces unreliable results.
  • Seat the patient comfortably. Instruct the patient to look straight ahead, keeping the eyes open and unblinking.
  • Instill topical anesthetic in each eye, as ordered, and allow time for it to work. Topical anesthetic drops are placed in the eye with the patient looking up and the solution directed at the six o’clock position of the sclera (white of the eye) near the limbus (gray, semitransparent area of the eyeball where the cornea and sclera meet). Neither the dropper nor the bottle should touch the eyelashes.
  • Request that the patient look straight ahead while the probe of the pachymeter is applied directly on the cornea of the eye. Take an average of three readings for each eye. Individual readings should be within 10 microns. Results on both eyes should be similar.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Recognize anxiety related to test results. Encourage the family to recognize and be supportive of impaired activity related to vision loss, anticipated loss of driving privileges, or the possibility of requiring corrective lenses (self-image). Discuss the implications of test results on the patient’s lifestyle. Reassure the patient regarding concerns related to impending cataract surgery. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Provide contact information, if desired, for the Glaucoma Research Foundation (www.glaucoma.org).
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include fundus photography, gonioscopy, intraocular pressure, and visual field testing.
  • Refer to the Ocular System table at the end of the book for related tests by body system.
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References in periodicals archive ?
c) The pachymetry measurement at the thinnest point
Optical or ultrasonic measurements of corneal pachymetry estimate the severity of the corneal oedema.
Assessment of CCT with other non-contact techniques like scheimpflug pachymetry and ultrasonic pachymetry will result in more reliable assessment of CCT.
In tissue bank, the lamellae are usually measured by ultrasound pachymetry, which is the gold standard for corneal thickness measurement.
Central corneal thickness was measured with an ultrasound pachymetry device for calculating corrected IOP.
Ultrasonic pachymetry is widely used to measure CCT, but this method has some disadvantages.
Pentacam and Galilei G4 are non-contact devices which make 2-D and 3-D images of anterior segment, measures corneal topography and pachymetry. Pentacam uses combination of slit illumination system and a rotating Scheimpflug camera to construct topographic images of anterior chamber of eye while the later uses a double Scheimpflug camera and a Placido topography system.
There were also differences in corneal pachymetry of 503 [micro]m in patients with DS versus 545 [micro]m in controls.
These include a visual-field test that checks peripheral vision, tonometry, which measures eye pressure, gonioscopy, which assesses the angle where eye fluid exists, and a pachymetry test that assesses the thickness of the cornea.
The IOP was determined using non-contact tonometry, and the central corneal thickness was measured using ultrasonic pachymetry.
These features include the measurement of pachymetry, points and amplitude of applanation, or the maximum cornea deformation.