Analysis Of Postoperative Astigmatism After Miniject Implantation In Microinvasive Glaucoma Surgery

The MINIject (iSTAR Medical, Wavre, Belgium) is a supraciliary microinvasive glaucoma surgery (MIGS) device intended for an ab-interno implantation in eyes with mild to moderate glaucoma. Previous studies showed a good safety and efficacy profile. However, nothing is known about potential refractive alterations resulting from the supraciliary implant. The aim of this study was to investigate the postoperative astigmatism after implantation of the MINIject using a multivariate 3-dimensional power vector analysis.

In total, 166 eyes with chronic primary open–angle glaucoma, 42 with pseudoexfoliative glaucoma, 13 with pigmentary glaucoma, 5 with uveitic glaucoma, and 24 with rarer diagnoses, treated at the Sulzbach Eye Clinic were included. A total of 169 eyes from 144 patients, 75 male and 69 female, received MINIject implantation as standalone procedure and 81, from 65 patients, 37 male and 28 female, in combination with cataract surgery. Mean age at surgery was 70 ± 13 and 70 ± 9 years, respectively.

Subjective refraction and corrected distance visual acuity (CDVA) were obtained preoperatively (D0) and at 3 months postoperatively (D90). Astigmatism was analyzed using a 3-dimensional power vector including the spherical equivalent M and the Jackson crossed cylinder projections to the 0° and 90° meridian (J₀) and to the 45° and 135° meridian (J₄₅). The blurring power vector “B” was calculated to estimate the strength of astigmatism. Exclusion criteria included myopia of <–6 diopters (D), hyperopia >+4 D, axial length < 22 and > 26 mm, a sulcus- or sclera-fixated IOL implantation, signs of eye diseases other than glaucoma and cataract, intraocular eye surgery within 6 months. Patients with a CDVA of 0.6 LogMAR or worse were also excluded.

Univariate analysis of refractive astigmatism showed no significant change over time neither after standalone implantation (D0: –1.5 ± 1.5 D vs. D90: –1.4 ± 1.2 D) nor after combined procedure (–1.3 ± 1.6 D vs. –1.0 ± 0.8 D). Spherical equivalent change was not significant in any cohort, although considerable after the combined procedure (–1.3 ± 4.1 D vs. –0.8 ± 1.2 D). Multivariate astigmatism analysis (M, J₀, J₄₅) demonstrated a significant change in astigmatism in the phacoemulsification cohort (P < 0.001) in contrast to the standalone procedure cohort (P > 0.05). The blurring power vector B significantly changed in the phacoemulsification (3.0 ± 3.2 vs. 1.2 ± 1.0) but not in the standalone procedure cohort (2.0 ± 2.3 vs. 2.0 ± 2.7).

This study indicates the MINIject implantation to be neutral in astigmatism as standalone procedure. By contrast, when combined with phacoemulsification it induces astigmatigmatic change, attributable to phacoemulsification and intraocular lens implantation. The 12 month data so far is consistent with the 3 month data but does not yet allow for conclusions, as follow-up is currently ongoing. Nevertheless, these results are important, as they show the astigmatism neutrality of this device. Thus, MINIject implantation retains the option of later refractive surgery and inversely when implanted standalone the MINIject should not compromise the outcome of a previous refractive treatment with patient satisfaction as a critical secondary endpoint.