Sunrise syndrome is a complication related to the intraocular lens (IOL) after cataract surgery. It refers to a condition where the IOL is subluxated upward due to the upper haptic being incorrectly placed in the ciliary sulcus and the lower haptic in the capsular bag.
Conversely, when the lower haptic is placed in the ciliary sulcus, it is called Sunset syndrome. The latter also occurs when the lower haptic escapes through a defect in the anterior capsule rupture, causing the IOL to shift downward.
Both syndromes are primarily caused by incomplete IOL fixation in the capsular bag. The most common cause is intraoperative misplacement of the haptics, but they can also occur late postoperatively due to ocular trauma, capsular bag rupture or contraction, or zonular rupture 1).
The prevalence of IOL dislocation or decentration is reported to be 0.1–1.7%, and major risk factors include history of vitrectomy, aging, high myopia, inflammation, retinitis pigmentosa, diabetes, mature cataract, history of acute angle closure, and connective tissue diseases 2).
Sunrise syndrome is a condition where the upper haptic is mispositioned in the ciliary sulcus, causing the IOL to subluxate upward, while Sunset syndrome is a condition where the lower haptic is mispositioned in the ciliary sulcus, causing the IOL to shift downward. Both are due to asymmetric IOL fixation, but there are differences in the intraoperative maneuvers and anatomical backgrounds that cause them.
Symptoms vary depending on the direction and degree of IOL subluxation and the stability of the eye.
Early/Mild
Decentration of the IOL optic: A decentered IOL within the pupil is observed under slit-lamp microscopy.
IOL oscillation during eye movement: The IOL oscillates with blinking or eye movements.
Anterior capsule contraction: Fibrous opacification can shrink the anterior capsulotomy opening, potentially promoting IOL decentration.
Progression/Severe
Optic dislocation out of the pupillary area: The IOL is observed in a position outside the pupillary area. Visual changes are prone to occur with postural changes.
Iris/uveal irritation: May cause pigment dispersion, iris transillumination defects, elevated intraocular pressure, inflammation, and hemorrhage (UGH syndrome)1).
Pupillary capture: Part of the IOL optic prolapses anterior to the iris, which can lead to pupillary block.
Ultrasound biomicroscopy (UBM) and anterior segment OCT are useful for evaluating the contact between the IOL and the iris1).
Asymmetric haptic placement is most often caused by intraoperative misoperation, but the following factors are also involved.
Secondary implantation, posterior capsule rupture, and mature cataract have been reported as major predisposing factors for IOL subluxation 1).
Compared to monofocal IOLs, multifocal and toric IOLs are more significantly affected by even minor decentration. In multifocal IOLs, even slight decentration can cause decreased visual acuity, optical aberrations, blurred vision, glare, and halos 1).
Diagnosis is primarily based on slit-lamp microscopy.
It is not always detectable. Even if the IOL is correctly fixed at the end of surgery, the haptic may dislocate from the capsular bag 2 to 3 weeks postoperatively. Under dilated slit-lamp observation, the misalignment between the pupil center and the IOL center may appear subtle, so continuous postoperative observation is important.
If the displacement is mild and does not significantly affect visual acuity or refraction, observation is an option. Even mild glare or monocular diplopia should prompt consideration of surgical intervention.
The surgical strategy for IOL malposition varies by case.
If the IOL falls into the vitreous cavity, it is retrieved using vitreous surgery forceps after total vitrectomy, floated to the iris plane using liquid perfluorocarbon (PFCL), and then removed.
The mechanism of sunrise syndrome is mainly due to incorrect placement of the haptics during surgery.
When a 3-piece IOL with angled haptics is placed upside down, or when asymmetric placement occurs with one haptic in the ciliary sulcus and the other in the capsular bag, the optic is displaced anteriorly. This results in:
In diffuse zonular dysfunction (e.g., exfoliation syndrome, history of vitrectomy), IOL-capsule complex dislocation may occur long after surgery. Asymmetric capsular contraction also contributes to decentration.
IOL malposition has been reported to cause chronic uveitis (pseudophakic iridocyclitis), with friction between the IOL and iris (iris chafing) serving as a persistent inflammatory stimulus3).
Research is progressing on surgical techniques that use intraoperative real-time OCT to confirm the positional relationship between the IOL and the capsular bag during surgery. Application is expected particularly in complex cases (e.g., posterior capsule rupture, zonular dialysis).
Sutureless intrascleral fixation (flange fixation) is attracting attention as a technique that eliminates the risk of late dislocation due to suture degradation, and its application to IOL dislocation cases is increasing. Further research is needed on long-term outcomes.
