Guide to Pentacam Holladay EKR Report

Here I will try to explain the Holladay (Equivalent Keratometry Reading ) EKR report, and how this report could help in biometry for IOL implantation, especially for patients who particularly had prior refractive procedure, or have irregular cornea. To interpret the Holladay EKR report, do ensure that your settings are proper as a wrong setting will lead to a false display and improper clinical judgement. The Pentacam comes with a default Holladay setting and users are recommended not to edit or tamper this default setting. Thus for a proper interpretation of the Hollday EKR report, the Holladay default settings are set to a calculation zone of 8 mm while the eccentricity calculation zone ( angle kappa, alpha) is also set to 8mm. The default depiction of the shape factor (SF) of cornea is Asphericiy (Q).

At the outset I need to explain what is meant by EKR (equivalent K reading) and how is it useful in a clinical practice for IOL calculation. Well, consider this:

• You take a K reading of the cornea for IOL calculation. Most keratometry machines, including optical biometry ( except IOL Master 700 with TK) would measure the anterior cornea only. This values are now used in a two variable formula like SRK T or Holladay I to generate the IOL power. These third generation two variable formulae will now deduct a certain power from the anterior K reading values that you have input as they recognize that corneal power measurements with a K Index value of 1.3375 may overestimate the total power of cornea. This is done by taking into account a fixed anterior to posterior corneal ratio (approximately 82 percent for normal cornea). If the patient's posterior cornea is not of average power, that is the anterior/posterior corneal ratio is abnormal, then the formula either overcompensates or undercompensates for the posterior corneal power while doing an IOL power calculation. This is what happens in Keratoconus or with patients with previous refractive laser surgery. That is why you will need a special formula for post Lasik patients.

• Explaining EKR - The average anterior and posterior corneal power are 48 D and -6.8 D (approximately). Let us assume that the patient in question has anterior/posterior corneal ratio lower than average. The Pentacam measures both anterior and posterior curvature of cornea, and measures posterior cornea as -6.5 D for this patient. Thus the patient's posterior cornea is -.3 D lower (less negative) than an average cornea. The EKR will therefore consider this and compensate for a weaker posterior corneal power and add .3D (adjust) to the anterior corneal values. The back surface of cornea has a negative power and therefore negates anterior corneal power. However, because the back surface of this patient's cornea is less negative (.3) than an average cornea, therefore the EKR will add to the anterior corneal power. The value derived of the anterior cornea ( K reading ) can then be directly input into any two variable standard IOL power calculation, regardless of the fact that this patient may have gone through a previous Lasik or has an abnormal anterior posterior ratio.

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