Effect of Gas Tamponade on IOL Position and Refractive Error after Phacovitrectomy
Shiraki N, Wakabayashi T, Sakaguchi H, Nishida K. Effect of Gas Tamponade on the Intraocular Lens Position and Refractive Error after Phacovitrectomy: A Swept-Source Anterior Segment OCT Analysis. Ophthalmology. 2020;127:511-5.
Phacovitrectomy, or combined phacoemulsification, intraocular lens implant (IOL) implantation, and pars plana vitrectomy (PPV), can be used over PPV alone as it may shorten surgery times, avoid intraoperative lens contact, and allow for faster visual recovery. There is concern for postoperative refractive errors in these patients, especially given possible forward movement of the IOL if gas tamponade has been used. Shiraki et al used swept-source anterior segment optical coherence tomography (SS-ASOCT) to evaluate the location of the IOL after cataract surgery or phacovitrectomy and examined the association with post-operative refractive outcomes.
This was a retrospective case series of 34 eyes that underwent cataract surgery, 20 eyes that underwent phacovitrectomy without gas tamponade for an epiretinal membrane, and 22 eyes that underwent phacovitrectomy with SF6 gas tamponade for a macular hole or a retinal detachment. Face down positioning was used for all patients with gas tamponade. Eyes were imaged preoperatively and at 1 week and 1 month postoperatively with SS-ASOCT to determine lens position. Refraction (spherical equivalent) was also performed 1 week and 1 month after surgery.
The overall mean refractive prediction error (ME; the post-operative actual refraction minus preoperative refraction predicted by the formula for the exact power of the implant IOL) was -0.22 D at 1 month postoperatively. It was significantly greater in the phacovitrectomy with gas tamponade group (-0.82 D) than in the cataract surgery group (0.08 D) as well as in the phacovitrectomy without gas tamponade group (-0.07 D; p<0.001). Based on measurements from SS-ASOCT, the forward movement of the IOL significantly correlated with a greater ME at 1 month (p<0.01). Of note, the mean IOL position in the phacovitrectomy with gas tamponade group was more forward than the other groups at postoperative month 1 but this position was actually improved from postoperative week 1.
The results of this study suggest that phacovitrectomy with gas tamponade can cause forward fixation of the lens. This myopic refractive error persists even after the gas has disappeared and likely represents the permanent position of the IOL. The authors suggest that this forward movement of the IOL is caused by buoyancy and surface tension of the gas and occurred despite purported face down positioning of the patients. This is a well-designed study that relies on SS-ASOCT to correct for possible confounders, such as axial length measurement inaccuracies. However, the clinical significance of this myopic shift is less clear, especially in patients with guarded visual prognosis due to macular holes or retinal detachments. Regardless, this information can be used to counsel patients preoperatively and better select an IOL for these cases.
