Axial length is the term used in ophthalmology to define the distance between the front and back of the eye.
It is essential to know this distance for the treatment of some vision defects.
En Área Oftalmológica Avanzada We explain below what the axial length of the eye is and how it is measured.
What is the axial length of the eye?
Axial length is the distance between the back and the front of the eye.
The axial length of the eye is measured through ocular biometry and the following techniques are often used to calculate this distance:
Ultrasonic biometry can be contact or immersion.
In this type of biometry, the biometer emits an ultrasound beam that is sent to the eye through a probe.
When the beam spreads uniformly in the ocular tissues, a wave-peak recording is produced which in a healthy eye corresponds first to the cornea, then to the anterior part of the lens, then to the posterior lens capsule, and finally , to the retina.
The examination yields a two-dimensional image of the structures of the eye and the sum of all of them allows the axial length of the eye to be obtained.
During immersion biometry, the specialist places a capsule on the patient's cornea in which serum is instilled and the biometric probe is inserted.
This method does not suggest direct contact with the cornea.
This technique is performed with an optical biometer that emits two coaxial 780nm infrared light beams.
The double beam combats sensitivity to longitudinal movements of the eye.
While the ultrasonic biometer measures the cornea-internal limiting membrane, the optical biometer measures the cornea-retinal pigment epithelium, this represents a difference of approximately 130 μm.
In this ocular biometry technique there is no direct contact with the patient's eye.
It can sometimes be difficult to perform axial length measurement with optical biometry if the patient has media opacity, hemorrhages, walleye and cataracts.
Also, the measurement in pseudophakic eyes it can be wrong, up to 4.00 mm, due to the reflection produced by the intraocular lens.
What are the normal values?
At birth, the human being has an axial length of 14 mm, but over time the ocular structure develops and this distance increases.
During the progressive development of the eye, the cornea and lens flatten and the axial length of the eye can increase up to 23 mm in adulthood.
In a normal structure, the eye would be +0,50 diopters in adolescence, otherwise it is possible that some refractive defect of vision
Do you have more doubts about the axial length of the eye? Contact us in Área Oftalmológica Avanzada and our experts will be happy to solve them.«Back to the glossary index