Cataract post-op patients can present with a myriad of optical complaints after surgery. Dysphotopsias are one of the most frequently mentioned concern at the day 1 postoperative visit. In short, dysphotopsias are the things that patients see but we as doctors cannot see.
The symptoms are thought to be a manifestation of light scatter off the IOL onto the retina. To the optometrist, there can be virtually nothing to see, as it will often occur after a perfect in-the-bag cataract surgery. This can be very disconcerting to patients, so it is important to educate them on the very likely transient nature of this condition. The incidence of dysphotopsias vary tremendously in current literature, but positive dysphotopsias are much more widely documented, while negative dysphotopsias have a much lower incidence.
Positive dysphotopsia
Positive dysphotopsias are perceived as glare, arcs, halos and streaks frequently in the temporal field of vision. The precise cause is a bit mysterious, but it is thought to be due to light hitting the square edge of the IOLs used in cataract surgery. Most of the IOLs in the U.S. are square-edged, which was a design that has been around for a few decades — originally intended to help decrease the incidence of posterior capsular opacification (PCO). While PCO now occurs less frequently, it may be at the cost of increased incidence of dysphotopsias.
Older PMMA IOLs with round-edge optics seem to cause little to no dysphotopsia. It’s likely that these IOLs disperse just as much stray light as modern lenses, it’s just that the round edge disperses it across a wider portion of the retina. Modern square-edge designs concentrate this stray light over a smaller portion of the retina, leading to perception of the light. The inherent downside to using PMMA IOLs is that they are not foldable, and the surgeon needs to make a much larger incision to get the IOL in at the time of cataract surgery.
Management options of positive dysphotopsias primarily involve counseling regarding neuroadaptation, but when this approach fails, pharmacological agents may be helpful. Miotics will constrict the pupil, perhaps minimizing the glare. We have found that off-label use of brimonidine can help during the neuroadaptation process. If neuroadaptation does not occur, which is rare, an exchange can be done for an IOL with a different index of refraction and less surface reflectivity. We have found exchanging an acrylic IOL for either PMMA or silicone can help resolve the most persistent positive dysphotopsias. It is critical that the decision to perform an IOL exchange is made prior to the patient undergoing a YAG capsulotomy, as prior YAG destabilizes the capsular apparatus enough to make an IOL exchange impractical. Therefore, in patients who complain about glare issues that developed immediately after cataract surgery, positive dysphotopsia should be ruled out as the cause rather than simply assuming the symptoms are caused by PCO.
Negative dysphotopsias
Negative dysphotopsias are described as a dark crescent, blinders or a shadow, almost always in the patient’s temporal vision. In the setting of cataract surgery, it’s important to differentiate this from a scotoma resulting from a retinal detachment. Negative dysphotopsias are, again, almost exclusively in the temporal field and, unlike a retinal detachment, they do not create a scotoma that can be identified either with confrontation or automated visual fields. Further, the perceived shadowing generated by negative dysphotopsias does not generally extend to the edge of a patient’s vision, rather it is described as line rather than curtain in the field. Patients often describe the symptom as though they have a glasses frame that they can perceive off to the side.
This shadowing is thought to result from several things. First, as with positive phenomenon, the square-edged, acrylic IOL index of refraction may play a role. Second, there is almost certainly a simple spatial cause as well. It’s thought that light that hits the capsulorrhexis may cast a shadow on the peripheral retina. Fortunately, the bony architecture of the orbital anatomy helps limit the light that may cause this shadowing in all quadrants except temporally, and, thus, perception of this shadow is almost always temporal. Some risk factors are very small pupils, high IOL powers and larger angle kappas.
While miotics are known to be helpful in positive dysphotopsias, they can exaggerate negative dysphotopsias. Pharmacological dilation can help improve negative dysphotopsia, but this is not a practical solution, given dilated pupils cause more glare and unwanted visual symptoms. Thick temple pieces on glasses can be helpful in resolving the problem, as the wider temples will mask perception of the shadow. Unfortunately, negative dysphotopsias are less likely than positive to spontaneously diminish with neuroadaptation.
If symptoms do not go away, there are a few surgical management options. One utilizes a surgical technique called “reverse optic capture.” In this case, the haptics still go in the capsular bag, but the optic of the IOL remains anterior to the capsule. This obscures the shadowing of the capsulorrhexis while still allowing the capsule to support the IOL in the eye. This may accelerate the formation of PCO, so it is wise to discuss this with the patient prior to the reverse optic capture. Knowing another procedure may need to be done can decrease anxiety when and if a YAG is needed.
Whether positive or negative, dysphotopsia symptoms can be anxiety-provoking and are among the chief sources of patient dissatisfaction after cataract surgery. While there are still parts of dysphotopsias that we do not understand, it is important for doctors to be able to reassure and educate patients that this phenomenon is not the result of a poor surgery and that there is a very good chance they will resolve on their own. Although it’s easier said than done, we encourage patients to avoid hyper-fixating on symptoms to allow for quicker neuroadaptation. Most symptoms will diminish within 4 to 6 months, but it is reassuring to patients to know that management options are available if the symptoms persist. As time goes on, it is possible the capsule will develop some peripheral fibrosis that will interfere with the pesky light rays.