Protocol - Contact Biometry
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.
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 manufacturers instructions to ensure quality control.
Availability
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 participants 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 participants 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 participants file.
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 manufacturers instructions to ensure quality control.
Requirements
| Requirement Category | Required |
|---|---|
| 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
Lifestage
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.
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
Chinese, English
Standards
| Standard | Name | ID | Source |
|---|---|---|---|
| Logical Observation Identifiers Names and Codes (LOINC) | Contact biometry proto | 62679-6 | LOINC |
| caDSR Form | PhenX PX110101 - Contact Biometry | 5971463 | caDSR Form |
Derived Variables
None
Process and Review
Not applicable.
Protocol Name from Source
University of Southern California, The Los Angeles Latino Eye Study (LALES), 2000-2003
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 Name | Variable ID | Variable Description | dbGaP Mapping | |
|---|---|---|---|---|
| PX110101_Contact_Biometry_Instrument_Model | ||||
| PX110101010000 | Contact Biometry Instrument Model | N/A | ||
| PX110101_Left_Eye_Axial_Length_1 | ||||
| PX110101030100 | Left Eye axial length reading measured, more | Variable Mapping | ||
| PX110101_Left_Eye_Axial_Length_2 | ||||
| PX110101030200 | Left Eye axial length reading measured, more | N/A | ||
| PX110101_Left_Eye_Axial_Length_3 | ||||
| PX110101030300 | Left Eye axial length reading measured, more | N/A | ||
| PX110101_Left_Eye_Cornea_Thickness_1 | ||||
| PX110101050100 | Left Eye cornea thickness reading measured, more | N/A | ||
| PX110101_Left_Eye_Cornea_Thickness_2 | ||||
| PX110101050200 | Left Eye cornea thickness reading measured, more | N/A | ||
| PX110101_Left_Eye_Cornea_Thickness_3 | ||||
| PX110101050300 | Left Eye cornea thickness reading measured, more | N/A | ||
| PX110101_Right_Eye_Axial_Length_1 | ||||
| PX110101020100 | Right Eye axial length reading measured, more | Variable Mapping | ||
| PX110101_Right_Eye_Axial_Length_2 | ||||
| PX110101020200 | Right Eye axial length reading measured, more | N/A | ||
| PX110101_Right_Eye_Axial_Length_3 | ||||
| PX110101020300 | Right Eye axial length reading measured, more | N/A | ||
| PX110101_Right_Eye_Cornea_Thickness_1 | ||||
| PX110101040100 | Right Eye cornea thickness reading measured, more | N/A | ||
| PX110101_Right_Eye_Cornea_Thickness_2 | ||||
| PX110101040200 | Right Eye cornea thickness reading measured, more | N/A | ||
| PX110101_Right_Eye_Cornea_Thickness_3 | ||||
| PX110101040300 | Right Eye cornea thickness reading measured, more | N/A | ||
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
Measure Protocols
| Protocol ID | Protocol Name |
|---|---|
| 110101 | Contact Biometry |
Publications
Reed, D. M., et al. (2023) Eye Dynamics and Engineering Network Consortium: Baseline Characteristics of a Randomized Trial in Healthy Adults. Ophthalmol Glaucoma. 2023 March; 6(2): 215-223. doi: 10.1016/j.ogla.2022.09.001