Jack Holladay, MD, MSEE was instrumental in describing the causes of negative dysphotopsias with his enigmatic penumbra explanation. Sam Masket MD also has been a pioneer in this topic with his explanation of the causes and the surgical management. And now there is an excellent study by Bonnie An Henderson MD and colleagues which proposes an orientation for single-piece acrylic IOLs which may produce less negative dysphotopsia by using the haptic-optic junction to block certain rays of light. Let’s review that study (and I encourage you to read the entire paper).
The study showed that on post-op day #1, patients with the proposed inferotemporal positioning of the haptic-optic junction had a lower rate of negative dysphotopsias when compared to patients who had the haptic-optic junction positioned vertically at the 6 to 12 o’clock meridian. Patients with silicone IOLs performed better than both groups of acrylic IOL patients with regards to negative dysphotopsias.
By post-op day #28, or about 1 month after surgery, there was no statistical difference between the rate of negative dysphotopsias between the two groups of acrylic IOL patients, meaning that orientation of the IOL was not critical at this time. This is a welcome finding for astigmatic patients because if we are using single-piece acrylic toric IOLs then their orientation is dependent on the axis of astigmatism and they cannot all be placed in the proposed inferotemporal position. It also gives us assurance that over the first month of healing, the negative dysphotopsias settle down to a very low rate.
Dr. Henderson’s findings make sense because on the first post-operative day, there is virtually no contraction or opacification of the anterior lens capsule. The haptic-optic junction at the inferotemporal position may block the penumbra effect explained so eloquently by Dr. Holladay. Then once a month has passed, the capsular bag has contracted and the anterior capsule leaflet has become more opaque, both of which may serve to decrease the penumbra effect.