Premium IOL centration and patient suitability

Proper centration of premium IOLs — diffractive multifocal, moderate to high toric, and aspheric — is critical to achieve the maximum optical performance and to avoid unnecessary symptoms of halos, glare and “waxy vision.” To understand and use the optical principles involved with these complaints, we must review the angles of the eye.In Figure 1, we see a cross-section of the eye from above illustrating that the foveola is temporal to the optical axis of the eye by a nominal 5.2°. From the front view of the eye in Figure 2, we see that the reflection of a penlight (white circle with blue cross known as Purkinje 1) with the patient fixating on the light and the observer coaxially viewing will be slightly nasal and is labeled visual axis (VA) because the line connecting the foveola with the object passes through this point on the cornea. The pupil center (PC) to VA is known as angle or more recently chord length . The angle between the optical center of the cornea (OC) and VA is angle . Arguments about determining these angles and chord lengths are not particularly helpful clinically, but are fully explained by Chang and colleagues. The clinician only needs to remember the image seen in Figure 2.