Welcome to LEDC>Patient Information>Biometry
BiometryTo measure the size and shape of the eye. Biometry measurements are used before cataract surgery to determine the most suitable lens to be implanted during the procedure.
Procedure:
The patient places their chin on a chin-rest and looks at a light on the machine. The operator takes measurements of the axial length (the length from the front to the back of the eye); the corneal curvature and the anterior chamber depth. If there is a very dense cataract we may need to use ultrasound to take the measurement. If this is the case, we put an anaesthetic drop into the eye before placing a probe lightly against the cornea.
How Long Will It Take?
Most tests take about 15 minutes but if the cataract is dense then this could take longer.
Preparation:
Contact lens must be removed before the measurement. If possible, wear glasses to the appointment instead.
Ocular Biometry is carried out in order to take measurements of the structure inside the eye. We are able to measure the distance from the front of the eye to the surface of the retina and also the thickness of the lens inside the eye. These measurements are often used by surgeons in order to improve the function of the eye after surgery. For example, during a cataract operation, the cloudy lens of the eye is replaced by a clear plastic implant. Biometry measurements are used in order to calculate the power of the replacement lens required to give the best unaided vision afterwards. The measurements are also used by surgeons carrying out corrective surgery on the front of the eye.At LEDC, we provide two different methods for taking these readings:
The Zeiss IOL Master combines axial length, corneal curvature and anterior chamber depth examination in a single machine. Measurements are taken along the visual axis to ensure the greatest accuracy, measuring to the nearest 0.01mm. Unlike ultrasound biometry, the machine makes no contact with the eye and reduces variability between operators. Internal processing by the machine checks the quality of each measurement and indicates unreliable data. All lens data and measurements are stored on the machine for easy recall. The lens database allows each consultant up to 4 lens constants to be used in the calculations.
This procedure involves the use of a local anaesthetic drop before the ultrasonic probe is applied to the front surface of the eye. By using keratometry information about the size and shape of the eye, we are able to calculate the measurements inside the eye. The results are available in a number of formats.
Some types of biometric measurement are used for other reasons. Corneal pachymetry is used to verify the accuracy of intra-ocular pressure measurements and keratometry is used to calculate the magnification of images taken of the back of the eye.