Toric Refractive Surprise Calculator
This calculator can be used in the setting of a refractive surprise following cataract surgery with the implantation of a toric IOL in order to plan how best to give the lowest refractive astigmatism.
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Assuming that the post-operative target for the patient was to have the lowest possible refractive astigmatism, it can be difficult to know what the best action is to take when this outcome is not achieved. This calculator requires an accurate post-operative subjective refraction, measurement of the anterior chamber depth, knowledge of the IOL sphere and cylinder power, and current position of the toric IOL axis. Keratometric data and the intended axis are not required. The calculator output provides a toric IOL axis to give the lowest refractive astigmatism. This may not be the same as the originally planned axis as it is based on the subjective refraction.
The other calculator output provided is the IOL-plane cylinder power required at the newly adjusted axis to give the lowest refractive astigmatism. The difference in power between the current cylinder power and that required is also shown. If the required cylinder power is greater than halfway to the next available cylinder power produced by your preferred IOL manufacturer, then an IOL exchange may be the best option to give the lowest refractive astigmatism. If the required cylinder power is less than halfway to the next available cylinder power produced, then rotation of the currently implanted IOL may be the best option to produce the lowest refractive astigmatism. These options are not mutually exclusive and potentially a different IOL cylinder power may be needed at an axis different to the current position to minimise refractive astigmatism.
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Record patient identification data.
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Record the current post-operative subjective refraction. This needs to be as accurate as possible so it is important to know that there are no confounding factors decreasing vision such as corneal oedema or macula oedema. This calculator uses a back vertex distance of 12.5mm.
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Record the post-operative anterior chamber depth, preferably measured by the same method used pre-operatively i.e. IOLMaster, Lenstar, Pentacam etc.
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Record the spherical power of the implanted IOL. This is the base sphere power and NOT the spherical equivalent of the lens. Note that Alcon toric IOLs most commonly have their spherical equivalent power recorded and this must be adjusted prior to inputting sphere power into this calculator. Zeiss toric IOLs most commonly have their base sphere power recorded which can be directly put into this calculator.
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Record the cylinder power of the IOL using plus cylinder notation.
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Record the current IOL axis (between 1 and 180 degrees)
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New Pre-redo astigmatic axis output provides the axis that the current toric IOL could be rotated to which would give the lowest amount of refractive astigmatism.
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Shortest Axis rotation required ouput indicates how many degrees the current toric IOL axis would need to be rotated to reach the axis output above. Note that positive numbers indicate counterclockwise rotation of the IOL.
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IOL Plane Cyl Power required output indicates the cylinder power of the toric IOL that would be required at the newly indicated axis to give the lowest refractive astigmatism.
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These output values may be used to help decide what the best management option is when a toric refractive surprise occurs. This may involve rotating the IOL to the newly indicated axis; exchanging the IOL for a different cylindrical strength or a combination of both.
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If the required cylinder power is greater than halfway to the next available cylinder power produced by your preferred IOL manufacturer, then an IOL exchange may be the best option to give the lowest refractive astigmatism. If the required cylinder power is less than halfway to the next available cylinder power produced, then rotation of the currently implanted IOL may be the best option to produce the lowest refractive astigmatism.
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Refractive surprises in spherical power are not analysed by this calculator. Alterations of IOL cylinder power will affect the spherical ​equivalent of the refractive outcome by approximately half the dioptric value of the cylinder power alteration. The surgeon should judge if that possible sphere equivalent outcome change is significant and adjust the IOL sphere power as they see fit.
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