Optical biometry is an essential part of cataract surgery planning. The purpose of ocular biometry is to measure the dimension of the eye. This includes the thickness of the ocular structures, the distance between structures, and the total length of the eye (axial length).

Measured ocular dimensions including central corneal thickness, anterior chamber depth, lens thickness, white-to-white, and axial length are used in IOL power calculation formulas to predict the necessary IOL power to produce the desired refractive outcome.

Optical biometry is also used for myopia management. Myopia is a growing health crisis with 50% of the global population projected to be myopic by 2050. Myopia is caused by excessive eye elongation (axial myopia) or steepening of the cornea (refractive myopia). Myopia causes increased dependence on visual aids, but axial elongation underlies the increased risk of future ocular disease. A range of myopia control methods including specialised spectacles, specialised contact lenses, pharmaceutical drops, and light therapy are now offered to slow the progression of myopia in children. Measurement of the axial length using optical biometry is a powerful tool for the myopia clinician. It can aid early detection of myopia, monitor for progressive axial myopia, and determine the efficacy of myopia control methods.

Optical biometry uses light waves to measure eye dimensions, making measurements highly precise and capable of measuring with high resolution. An advantage of optical biometry is that it is a non-contact procedure, eliminating any risk of corneal compression for accurate axial length measurements and providing better patient comfort. Patients are instructed to maintain their gaze on the fixation light to ensure measurements are made along the visual axis.

Ultrasound biometry uses sound waves. Sound has a long wavelength providing excellent penetration through ocular tissues. This makes measurements possible through dense cataract, whereas light has poor penetration. There are two types of ultrasound biometry: contact and immersion. Contact ultrasound requires the probe to touch the surface of the cornea. This risks corneal compression thus potentially underestimating the axial length. Immersion ultrasound is performed with the probe sitting in a bath of saline which acts as a coupling fluid. As the probe sits away from the cornea, the risk of corneal compression is eliminated. The disadvantage of the immersion ultrasound is that it requires a highly trained operator to ensure correct handling of the scleral shell to maintain the bath of saline round the probe. 

Optical biometry is accurate, improves on axis measurements, and is more tolerated by patients making it the standard of care today in cataract surgery planning.

Lenstar 900 and Eyestar 900 are optical biometers ideal for taking ocular biometry measurements.

Other complementary devices include:

• ultrasound biometry for particularly dense cataracts, if biometry needs to be done under general anaesthesia or if the patient has postural challenges that prevent them from sitting at the chinrest
• corneal topographer, unless one is built into the biometer being used
• autorefractor or glasses vertometer to measure the patient’s refraction, to validate biometry measurements.

Optical biometry will be undertaken by a trained operator in a slightly dimmed room. The operator will adjust the table and guide you to the correct position on the chinrest to ensure you are aligned with the device. You will be instructed to keep looking on the light in front of you. It is important to follow the instructions of the operator as they will instruct when it is appropriate to blink and when it is important to hold your eyes open. You can expect up to five flashes of light per eye depending on the device used. The duration of the scan will also depend on the device used. On average, Eyestar 900 takes 45 seconds to scan both eyes. Lenstar 900 can take between 2-5 minutes for both eyes, depending on operator experience. The measurement may be repeated depending on the reliability of the scan. A drop of saline may be applied to the eyes to improve the quality of the scan.

Corneal topography is a diagnostic imaging technique to measure the cornea’s shape. The results are depicted as colour coded maps to represent the 3D structure of the cornea. Corneal topography has a wide range of applications for example, measuring astigmatism, detecting corneal irregularities, monitoring corneal diseases, and in assessments for corneal refractive surgery.

One method of topography is Placido disc topography which is the basis of the Lenstar 900’s T-cone accessory. Concentric dark and bright rings are projected on the anterior surface of the cornea and the reflected image in captured with a camera. As the cornea acts as a convex mirror, the reflected rings will be spaced closely in areas of steep cornea and spaced widely in areas of flatter cornea. 

Tomography with optical coherence tomography (OCT), which can be performed with Eyestar 900, has the advantage of measuring both the anterior and posterior surface of the cornea. Measuring the posterior cornea is useful for detecting early signs of keratoconus and for improved IOL calculation in eyes with previous corneal refractive surgery. OCT scans rapidly across the surface of the cornea and through the cornea to construct cross-sectional scans of the corneal.

There are several types of topography maps. Axial topography maps provide an overview of the corneal shape but lacks detail due to a smoothing effect. Tangential maps may more accurately depict the corneal shape by revealing localised irregularities on the corneal surface. Elevation maps represent the height of the cornea relative to the best fit sphere. Enhanced elevations maps may also better highlight localised areas of elevation.

Corneal topography maps are colour coded to represent the 3D shape of the cornea in a 2D manner. In axial and tangential maps, warmer colours represent steeper areas while cooler colours represent flatter areas. In elevation maps, warmer colours represent areas of elevation while cool colours represent areas of depression.

To interpret topography maps, consider which colours are present, where the colours are distributed, and whether the distribution of colours form a pattern typical of certain corneal conditions. Regular corneal astigmatism appears as warmer colours distributed in a symmetrical ‘bowtie’ pattern with the orientation of the bowtie representing the axis of astigmatism.   

Reflective keratometry is essential for measuring corneal power and astigmatism, contact lens fitting, diagnosing and monitoring corneal ectatic conditions like keratoconus, and calculating the correct IOL power.

Keratometry is the measurement of the radius of curvature of the central cornea. A pattern of lights (mires) are projected onto the surface of the cornea. Lenstar 900 and Eyestar 900 use a double ringed pattern consisting of 32 points. Modern keratometers use cameras to capture and measure the size of the image reflected by the cornea. As the cornea acts as a convex mirror, relatively steeper areas of the cornea will produce more minification than the flatter areas. Keratometry will provide the steepest and flattest meridian. The radius of curvature is then converted to the corneal dioptric power using the standard keratometric index of refraction 1.3375. 

Keratoconus is a corneal condition in which there is progressive steepening and thinning of the cornea, typically developing in adolescence.

This may appear as: 

• K readings <47D

• a localised, possibly inferior decentred, zone of warm colour on the axial/tangential map in the anterior and/or posterior cornea representing steepening of the cornea

• a localised, possibly inferior decentred, zone of warm colour on the elevation map in the anterior and/or posterior corne

• a thinner than average central corneal thickness

• the thinnest point of the corneal centred in the localised zone of steepening/elevation

• a Corneal Thickness Profile and Corneal Percentage Thickness Increase plot that deviates away from average

• a highly negative Q value (normal values are between -0.2 and -0.4)

• changes to topographic indices, CCT, CTP across successive maps suggesting progression.

A clinician should also perform thorough history taking, objective and subjective refraction, and assess the eye with a slit lamp to look for other keratoconus changes to the eyes.

Swept-source OCT is the newest generation of OCT technology used in ophthalmic imaging to diagnose various eye diseases. Swept source OCT utilizes a wavelength-tuning laser light source to enable long range, high resolution, and rapid cross-sectional scanning of the eye.

It is the technology behind the Eyestar 900, allowing quick biometry acquisitions, full corneal tomography, and 360-degree visualization of the anterior segment.

For information on how to do this, please see the video on the HS-UK YouTube channel.

Yes, it does. The PC needs to be on your network and you will need to check with the third party EMR software supplier to see if any fees may apply.

The cost of a Lenstar will depend on your needs and what optional additions you might require. For a full quotation, please contact our customer services team on 01279 883720 or email info.unitedkingdom@haag-streit.com.

The Lenstar features dual zone keratometry as standard and T-Cone topography for precise astigmatism and axis measurement in an additional T-Cone module. 

Lenstar PRO comes with toric planning software, an intuitive tool for toric interventions. For further information, please visit the HS-UK dedicated Lenstar webpage.

The Lenstar automatically enables Dense Cataract Measurement (DCM) mode and has a very high penetration rate with dense cataracts. Clinical studies to support this are available to view at https://pubmed.ncbi.nlm.nih.gov/26210047/. 

Instructions on this can be found in the two videos below or the Quick Guide document:

Video 1 – Entering Spherical IOLs in EyeSuite version i9.

Video 3 – Entering Toric IOLs in EyeSuite version i9.

IOL Template Configuration Quick Guide.

Yes, it does. Eyestar provides Class A topography covering up to 12mm of the anterior and posterior cornea to improve surgical planning. Inclusion of posterior cornea measurements has the potential to provide more accurate IOL calculation particularly for astigmatic and post-refractive patients. Independent assessment of the posterior cornea with ectasia maps may enable earlier detection of cornea disorders.

Eyestar provides comprehensive tools to determine your patient's suitability for premium IOLs. This includes front and back surface corneal topography, assessment of lens tilt and Zernike analysis of the anterior cornea wavefront aberrations. 

Eyestar with EyeSuite is fully networkable with your own practice network to allow access to measurements from any workstation. EyeSuite also works with DICOM standard to produce reports such as e-PDF or multi-frame color images which can be viewed by any device. 

The cost of an Eyestar will depend on your needs and what optional additions you might require. For a full quotation, please contact our customer services team on 01279 883720 or email info.unitedkingdom@haag-streit.com.

The HS-UK Service Department has a comprehensive range of service contract options available for your Lenstar or Eyestar biometer, as well as ad-hoc repair solutions in response to a breakdown or faulty equipment. As the authorised UK service agent of the Haag-Streit Lenstar, we use only specialist manufacturer tools to check for free and correct movement of all axes, carry out a complete measurement check and a full polarisation calibration. Visit our HS-UK Service Division pages to find out more about taking out a service contract.