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Protocol - Contact Biometry

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Description:

The axial length of the eye and central corneal thickness is measured in this protocol using the Ultrasonic A scan/pachymeter DGH 4000B SBH IOL Computation module. (A-Scan pachymeter, Ultrasonic, Exton, PA) which requires direct contact with the cornea. Three measurements are taken on each eye for both axial length and central corneal thickness. Results of all measurements are then printed.

Protocol:

Procedure for Measuring Corneal Thickness (Pachymetry)

1. Plug in the pachymeter probe.

2. Turn on the power switch.

3. Disinfect the probe in accordance with the guidelines from the Center for Disease Control.

4. Have the participant seated in a comfortable position.

5. Prepare the cornea by instilling one drop of anesthetic in the participant's inferior cul-de sac.

6. Instruct the participant to open both eyes and look straight ahead.

7. Press ENTER for OD (Right Eye).

8. Gripping the hand piece, move the probe toward the cornea, and gently touch the central part of the cornea. The machine will make a characteristic sound to indicate a completed reading.

9. Repeat the procedure 2 more times, until 3 readings are obtained.

10. Print the readings by pressing the PRINT button.

11. Press CLEAR.

12. Press SELECT for OS (Left Eye).

13. Press ENTER twice.

14. Take 3 readings.

15. Press PRINT.

16. Enter the data in the computer and attach the printed results to the participant's file.

Procedure for Measuring Axial Length (A Scan)

1. Plug in the A-Scan probe.

2. Press the AUTOGAIN button.

3. Press ENTER (to select OD, Right Eye).

4. Press SELECT to specify if the lens is normal or cataractous, or if the participant is aphakic, or pseudophakic. If pseudophakic, select the type of intraocular lens, then press ENTER.

5. Take 3 readings.

6. Press PRINT.

7. Press CLEAR.

8. Press SELECT (to select OS, Left Eye).

9. Press ENTER.

10. Press SELECT to specify if the lens is normal, cataractous, or if the participant is aphakic, or pseudophakic. If pseudophakic, select the type of intraocular lens, then press ENTER.

11. Take 3 readings.

12. Press PRINT.

13. Turn the power off.

14. Enter the data in the computer and attach the printed results to the participant's file.

Protocol Name from Source:

The Expert Review Panel has not reviewed this measure yet.

Availability:

Publicly available

Personnel and Training Required

Trained ophthalmic technician or ophthalmologist

Equipment Needs

Ultrasonic A scan/pachymeter DGH 4000B SBH IOL Computation module (A-Scan pachymeter, Ultrasonic, Exton, PA)

Note: This protocol for contact biometry uses the ultrasonic A scan/pachymeter DGH 4000B SBH IOL Computation module. Other instruments can be used to measure ocular biometry including axial length and central corneal thickness. If other instruments are used, the reproducibility of the measurements should be comparable to those acquired with this protocol. In addition, when other instruments are used to collect these measurements, the manufacturer and model of equipment should be recorded. These other devices may require some different steps than are described in this protocol. Investigators should follow the equipment manufacturer's instructions to ensure quality control.

Requirements
Requirement CategoryRequired
Major equipment Yes
Specialized training Yes
Specialized requirements for biospecimen collection No
Average time of greater than 15 minutes in an unaffected individual Yes
Mode of Administration

Clinical Measurement

Life Stage:

Adult

Participants:

Adults aged ≥ 40 years

* While this protocol was used in a study of adults aged ≥40 years, the Ocular Working Group suggests that the same methodology can be used for individuals aged 18 years and older.

Specific Instructions:

The WG recommends that three readings be taken and recorded from each eye for both axial length and central corneal thickness (measurements in millimeters).

The WG recommends that the central corneal thickness-pachymetry measurements be taken first followed by the axial length measurements, as presented in this protocol.

This protocol for contact biometry uses the ultrasonic A scan/pachymeter DGH 4000B SBH IOL Computation module. Other instruments can be used to measure ocular biometry including axial length and central corneal thickness. If other instruments are used, the reproducibility of the measurements should be comparable to those acquired with this protocol. In addition, when other instruments are used to collect these measurements, the manufacturer and model of equipment should be recorded. These other devices may require some different steps than are described in this protocol. Investigators should follow the equipment manufacturer's instructions to ensure quality control.

Selection Rationale

This assessment will provide information on ocular axial length, anterior chamber depth, lens thickness, posterior chamber depth and central corneal thickness. All of these measures can be genetically influenced. The protocol selected is a standard, well-characterized procedure used in adult (over the age of 18) populations.

Language

English

Standards
StandardNameIDSource
Common Data Elements (CDE) Eye Contact Biometry Axial Length Number 3008662 CDE Browser
Logical Observation Identifiers Names and Codes (LOINC) Contact biometry proto 62679-6 LOINC
Derived Variables

None

Process and Review

The Expert Review Panel has not reviewed this measure yet.

Source
University of Southern California, The Los Angeles Latino Eye Study (LALES). 2000-2003.
General References

Varma R, Paz SH, Azen SP, Klein R, Globe D, Torres M, Shufelt C, Preston-Martin S; Los Angeles Latino Eye Study Group. (2004). The Los Angeles Latino Eye Study: design, methods, and baseline data. Ophthalmology, 111(6):1121-31.

Shufelt C, Fraser-Bell S, Ying-Lai M, Torres M, Varma R; Los Angeles Latino Eye Study Group. (2005). Refractive error, ocular biometry, and lens opalescence in an adult population: the Los Angeles Latino Eye Study. Invest Ophthalmol Vis Sci, 46(12):4450-60.

Protocol ID:

110101

Variables:
Export Variables
Variable NameVariable IDVariable DescriptionVersiondbGaP Mapping
PX110101_Contact_Biometry_Instrument_Model PX110101010000 Contact Biometry Instrument Model 4 N/A
PX110101_Left_Eye_Axial_Length_1 PX110101030100 Left Eye axial length reading measured, first measurement 4 N/A
PX110101_Left_Eye_Axial_Length_2 PX110101030200 Left Eye axial length reading measured, second measurement 4 N/A
PX110101_Left_Eye_Axial_Length_3 PX110101030300 Left Eye axial length reading measured, third measurement 4 N/A
PX110101_Left_Eye_Cornea_Thickness_1 PX110101050100 Left Eye cornea thickness reading measured, first measurement 4 N/A
PX110101_Left_Eye_Cornea_Thickness_2 PX110101050200 Left Eye cornea thickness reading measured, second measurement 4 N/A
PX110101_Left_Eye_Cornea_Thickness_3 PX110101050300 Left Eye cornea thickness reading measured, third measurement 4 N/A
PX110101_Right_Eye_Axial_Length_1 PX110101020100 Right Eye axial length reading measured, first measurement 4 N/A
PX110101_Right_Eye_Axial_Length_2 PX110101020200 Right Eye axial length reading measured, second measurement 4 N/A
PX110101_Right_Eye_Axial_Length_3 PX110101020300 Right Eye axial length reading measured, third measurement 4 N/A
PX110101_Right_Eye_Cornea_Thickness_1 PX110101040100 Right Eye cornea thickness reading measured, first measurement 4 N/A
PX110101_Right_Eye_Cornea_Thickness_2 PX110101040200 Right Eye cornea thickness reading measured, second measurement 4 N/A
PX110101_Right_Eye_Cornea_Thickness_3 PX110101040300 Right Eye cornea thickness reading measured, third measurement 4 N/A
Research Domain Information
Measure Name:

Contact Biometry

Release Date:

February 26, 2010

Definition

Axial length of the eye and central corneal thickness is measured using contact biometry and pachymetry. Depth of the anterior chamber, lens thickness and depth of the posterior chamber can also be obtained.

Purpose

Many eye diseases are known to be associated with either excessively short eyes (nanophthalmos and angle closure glaucoma) or excessively long eyes (degenerative myopia, Stickler's Syndrome). In addition, ocular biometry provides information about the thickness of the lens (for studies of cataract) and the size of the posterior chamber. Axial length of the eye is an essential measurement for selecting the proper intraocular lens when doing cataract surgery. Central corneal thickness influences intraocular pressure measurements (thicker corneas result in artificially higher pressure and thinner corneas in lower pressure). In addition thinner central corneal thickness may be an independent risk factor for optic nerve degeneration in glaucoma.

Keywords

Ocular, Eye, Biometry, Axial length, Los Angeles Latino Eye Study, LALES, Central corneal thickness, Pachymetry, Depth of the anterior chamber, Lens thickness, Depth of the posterior chamber