Most Accurate Cataract Surgery (MACS)

Eye Measurements

Look for an ophthalmologist who takes more than the two standard measurements required for Medicare reimbursement: one axial length reading (from the front of the cornea to the retina) and one keratometry reading, known as K reading (measures average curvature of the cornea).

Remember that eyes are like fingerprints, in that no two are alike. They’re filled with many complex structures that can have their own unique shape and size. So a doctor only taking two measurements for cataract surgery would be like having a tailor only measure your height and waist for a suit: the fit might not be right.

With Most Accurate Cataract Surgery (MACS), your doctor will take many more important measurements to provide a more accurate determination of both the lens power that’s right for you and exactly where in your eyes your replacement lenses shoud be implanted.

Some MACS measurements are covered by Medicare. As a part of the initial consultation, your doctor will help determine exactly what is covered, based on your individual circumstances. Learn more about insurance coverage.

Find a MACS specialist near you.

To see a diagram of each measurement, simply roll over the word.

Click on a measurement in the list above to see it's description.

Axial Length / Keratometry (projected light reflections)

Medicare covers ONE measurement of the Axial Length. Many MACS surgeons like to have multiple measurements of the Axial Length to double and triple check the dimension of the Axial Length of the eye.

Keratometry measures the “average” corneal curvature found in the cornea and helps identify Corneal astigmatism. Again, Medicare covers ONE measurement here. MACS surgeons will take multiple measurements of the cornea with Keratometry instruments (manual and automated to make sure we have a good measurement number).

Retina Thickness

The measurement of the thickness of the Retina and health of the retina is important to determine how much visual function you might have in the development of the image you see. It’s like studying the film development found in a camera — you can have the best optics in front of the film development, but it won’t matter, if the developer is not in top shape. Most MACS surgeons will measure the retina thickness and health to consult with the cataract patient about their ability to benefit from the MACS procedure. With some exceptions, patients who do not have a healthy retinal function are NOT candidates for the MACS procedure. Medicare does not reimburse for this test without a medical indication and MACS surgeons might do this test without any medical indication, just to be sure about your retinal health.


Optical Coherence Tomography is the digital image testing for the health and wellness of your retina. This test is reimbursed by Medicare but, not for the basic cataract operation. The MACS surgeon may elect to do this diagnostic test and digital photography, just to make sure again that the retina is able to capture good quality images produced from the MACS cataract operation. If the health of the retina from this test is found to not be of the highest quality, the MACS procedure will not benefit the patient in it full extent and the MACS surgeon will discuss the best end-point that can be achieved.

Scheimpflug Imaging

MACS surgeons may elect to measure the lens width and the distance exactly where the IOL implant will rest. This test is not reimbursed by Medicare for cataract and is not medically necessary to the procedure, but may allow the MACS surgeon to better predict the power selection for your MACS IOL.

Pupilometry (diameter of the pupil)

Pupilometry measurement helps the MACS surgeon see how much of the IOL implant optic is going to be functional with your eye. Some patients have pupil sizes that expand very wide, therefore using the whole IOL optic and others only dialate to a limited size. With this information, your MACS surgeon may be better equipped to predict your post-operation optical effectiveness for MACS procedure vs the Basic cataract operation.

Lens Thickness

This is a new area of diagnostics and many MACS surgeons like to also get the thickness of the cataract lens to better determine where in the eye the IOL is going to eventually rest. This measurement is not covered by Medicare and may require another testing device in the pre-operative work-up for the MACS procedure. This will vary by doctor to doctor when looking at this measure and how they achieve the number.

Specular Microscopy

This measurement is taken with a high power microscope that can see the single cells found in the inside of the cornea. The more cells you see, the healthier the cornea is, the less cells the less healthy the cornea. When the cornea reaches a certain low point on cell count, the cornea health is in question and therefore the best possible vision may not be attended with the MACS procedures. Medicare pays for this measurement only on patients who are suspected to have low corneal cell count. The MACS surgeon may or may not elect to perform this test on the MACS cataract patient depending on the vision exams. Medicare does not reimburse this test without any predetermined need.


Pachymetry is used to measure here to really fine-tune the axial length measurement and determine how much the distance between cornea and the back of your eye might influence the power selection of your IOL implant.

Wavefront Measurement

This measurement is done by the refractive MACS surgeon’s to determine the high order aberrations within the optical system of your eye. All other formula’s used for cataract surgery assume there is no difference in high order aberrations within the eye and use an average measurement or measurement without any high order aberrations.

Tear Film Testing

There are a number of tests to determine the health of the patients tear film. Your tears are one of the most important parts to a quality vision outcome after cataract surgery. The MACS surgeon and doctor will want to make sure your tears are in good health. Medicare does not always cover these tests. It is a matter of your provider and costs associated with the tests used by your doctor.


White-To-White is a measurement of the distance from one side of the cornea to the other side (where the white part of your eye meets the clear cornea on each side). This measurement can help determine the diameter inside the eye where the IOL implant sits and can help determine the numbers used in new technology formulas used to get the MACS power calculation for your IOL power to best use for your surgery. Some instruments do measure this, some do not. So, this measurement on it’s own is not covered by Medicare, but might be covered with the instrument your doctor would use for Axial Length.

Topographic Map

Many MACS surgeons will use a Topographer to measure the total corneal topography to see all surface curvatures across the whole cornea and identify any irregular shape on the corneal surface that might interfere with good quality vision after Cataract surgery. With this test, the MACS surgeon may find you need astigmatism correction and this refractive procedure can also be combined with your MACS cataract procedure (also a non-covered procedure by Medicare).

Next: Replacement Lenses