Changes in biometric parameters of the eye following glaucoma surgery

PURPOSE: To assess the impact of trabeculectomy, Ex-PRESS shunt and Ahmed valve implantation on biometrical values of the eye.

METHODS: The study included 196 patients divided in

3 groups: trabeculectomy (TE) group (n=116), Ex-PRESS shunt (EXP) group (n=28) and Ahmed glaucoma valve (AGV) group (n=52). Each patient underwent optical biometry (keratometry, axial length, anterior chamber depth), autorefractometry (Topcon-8800) intraocular pressure (iCare) and standard ophthalmological examination prior to the surgery, 1 month and 6 months after. Preoperative and postsurgical data were compared to assess biometric values changes.

RESULTS: There was a mild decrease of mean keratometry 6 months after AGV implantation (from 44.08±1.06 to

43.94±1.21 D, p=0.023). On the contrary, TE increased corneal refractive power (from 44.39±1.13 to 44.55±1.09 D, p<0.001) 1 month after the surgery. There were no significant changes in EXP group. Steep meridian curvature increases by 0.28±0.59 D (p=0.002) 6 months after TE. EXP implantation induced flattening of weak corneal meridian (by 0.28±0.37 D 6 months after the surgery, p=0.003) as well as AGV group (decrease on 0.14±0.38 D, p=0.036). There were no significant changes in steep meridian axis in TE and EXP groups. However, AGV implantation leads to steep meridian axis bias from

88.6±50.5 to 71.4±48.9° (p=0.057). TE and EXP induced mild axial length (AL) reduction (by 0.09±0.19 mm, p<0.001 and by 0.08±0.1 mm, p<0.001 for groups respectively) 6 months after the surgery. AL shortening in AGV group was insignificant (by 0.08±0.4 mm 6 months after procedure). There was no significant difference in anterior chamber depth (ACD) before and after the surgery for all study groups.

CONCLUSION: Impact of glaucoma surgery on main biometrical values used to IOL power calculation (keratometry, AL, ACD) could lead to refractive errors after phacoemulsification. Thus, biometry for patients who require cataract extraction should be performed not earlier than 6 months after glaucoma surgery.

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