Ophthalmic Axial Length Attribute
| Tag | (0022,1019) |
|---|---|
| Type | Required (1) |
| Keyword | OphthalmicAxialLength |
| Value Multiplicity | 1 |
| Value Representation | Single (FL) |
The axial length measurement acquired, in mm.
The type of measurement is specified in the Ophthalmic Axial Length Measurements Type (0022,1010).
See Section C.8.25.14.1.1.3 and Section C.8.25.14.1.1.4 for further explanation.
Section C.8.25.14.1.1.3
C.8.25.14.1.1.3 Ophthalmic Axial Length
If Ophthalmic Axial Measurements Device Type (0022,1009) is ULTRASOUND, the Ophthalmic Axial Length (0022,1019) measurement is taken from the anterior vertex of the cornea to the anterior surface of the retina (internal limiting membrane).
If Ophthalmic Axial Measurements Device Type (0022,1009) is OPTICAL, the Ophthalmic Axial Length (0022,1019) measurement is taken from the anterior vertex of the cornea to the level of the photoreceptors in the retina and compensated to adjust for the thickness of the retina to mimic the ultrasound technique.
This difference is an inherent property of the measurement method. Since optical devices measure to retinal pigment epithelium and ultrasound devices measure to internal limiting membrane, the difference must be subtracted to obtain comparable results for use in intraocular lens calculation formulas. The difference is the thickness of the retina, which has been determined empirically and varies with the axial length of the eye.
The intent is to measure along the patient's visual axis.
Section C.8.25.14.1.1.4
C.8.25.14.1.1.4 Ophthalmic Axial Length Measurements Segment Name Code Sequence
When the acquisition device type is ultrasound, the Ophthalmic Axial Length (0022,1019) may represent distance calculated using a single time value and an average presumed velocity for the entire eye. Alternatively it may represent the sum of multiple segmental axial length measurements with each distance value calculated using a different time value and a presumed velocity specific to that segment of the eye.
When the acquisition device type is optical, the whole length can be measured instead of measuring and summing up different segments of the eye. Nevertheless, optical axial measurement devices can also measure segments of the eye independently (e.g., the Anterior Chamber depth).
Each segment of the eye that is measured shall be identified by the Ophthalmic Axial Length Measurements Segment Name Code Sequence (0022,1101).