At present, surgery is the mainstay for clinical treatment of PAC or PACG with coexisting cataracts. However, the discrepancy between the expected and the postoperative visual image quality is a source of patient dissatisfaction [13, 16]. In a retrospective case-control study, more refractive errors were found in PACG patients than in single cataract and primary open-angle glaucoma patients after phacoemulsification; it was thought that the shallow ACD and short AL structure of PACG resulted in poor accuracy of refraction . Meanwhile, high-order aberrations have been documented to affect postoperative visual quality [7, 8]. There is a paucity of studies assessing the corneal high-order aberrations and ocular biological characteristics changes in PAC or PACG patients with concomitant cataracts in different axial eye lengths. In the present study, we focused on the changes after Phaco-IOL-GSL, sought to better understand the variations in outcomes and help ophthalmologists select appropriate IOLs to improve the visual quality of this patient population.
Several studies have demonstrated that surgery could increase the risk of corneal higher-order aberrations, mainly due to the size and location of the incision and subsequent corneal tissue deformation and endothelial damage [9, 18, 19]. In a randomized controlled trial, Marcos et al.  inserted two types of monofocal IOLs through 3.2 mm superior corneal incisions during cataract surgery in patients. They found corneal trefoil and tetrafoil were significantly increased, and neither spherical aberration nor coma have this phenomenon. More comprehensive results were obtained in the present study since we measured the changes of the anterior surface, posterior surface, and total cornea aberrations. We found an increase in HOAs in the anterior surface and total cornea in both groups, especially for Z (3,-3). The change in anterior corneal surface HOAs was consistent with the total cornea, while the posterior corneal surface HOAs contributed only a small proportion to the total corneal, suggesting changes in posterior corneal aberration exerted little effect on long-term visual quality. It has been reported that corneal inflammation, edema or the remolding of the endothelial cells may lead to HOA changes on the posterior corneal surface during the early stages of surgery; however, these changes gradually disappear over time [18, 20]. Our study have neglected the impact of time on these changes since longer follow-up times. In addition, we found that increments of the anterior surface and total cornea Z (3,-3) differed in both groups while the changes of other HOAs were similar. Previous studies have found that trefoil was related to AL and axial elongation, and it usually is fortified after surgery and would not compensate by the internal optics of the eye [21, 22]. A recent study compared two types of incisions in cataract surgery and found that minimizing the incision size could reduce the aberrations, especially trefoil . Our study indicated the HOAs increased after Phaco-IOL-GSL, especially anterior cornea surface and total cornea Z (3,-3) at one-year follow-up, and varied according to the AL.
The last postoperative manifest refraction showed that both groups were inclined to drift towards hyperopia. However, only changes in the normal axial group were statistically significant (P = 0.002). Cataract surgery is a procedure where the lens is removed, and a pupillary block is relieved, deepening the anterior chamber. According to Ning et al. , patients with shorter preoperative ACD and AL would experience greater changes in ACD and hence be prone to drift towards myopia after cataract surgery. In contrast, patients with deep preoperative anterior eye chambers and long AL were prone to drift towards hyperopia. These findings indicated that ACD was a predictor of refractive outcomes after age-related cataract surgery. Many studies considered that ACD was an indicator of the position of the IOL postoperatively, and each additional 1 mm change in the ACD could lead to at least 0.32D of refractive shift [23, 24]. In the present study, we found that hyperopic drift positively correlated with the increment of ACD (r = 0.373, P = 0.001) and the decrement in AL after glaucoma surgery was positively correlated with the hyperopic drift (r = 0.331, P = 0.002).
Interestingly, changes in AL after glaucoma surgery have been associated with the use of antimetabolites, decreased IOP accompanied by choroidal thickening and surgical complications such as hypotony maculopathy . This process may not be observed in patients with only age-related cataracts without PAC or PACG. Osamah Saeedi et al. found that as IOP decreased after trabeculectomy, the AL became shorter, and the choroidal thickness increased in all PACG patients. It was thought that scleral relaxation after decreased IOP and decreased pressure exerted on the choroid caused the decrease in AL . Moreover, Maul et al. examined glaucoma patients with spectral-domain optical coherence tomography and found that the ocular perfusion pressure level influenced the choroidal thickness. As the IOP was decreased, the blood volume of the choroid increased, and the choroid became thicker . As we know, AL and ACD are two important factors which impact refractive errors after Phaco-IOL-GSL, while choroid thickness and IOP influence maybe the reasons for those changes. Moreover,removal of cataract can lead to deepening of ACD and subsequent hyperopia shift in PACG when an IOL is implanted in a more posterior plane than preoperatively planned . Although both groups exhibited an incline to drift towards hyperopia after the operation, the individual refractive direction was uncertain. Perhaps the large size of the lens capsule or the tilt or eccentricity of the IOL resulted into an ineffective lens position . Many researchers agree that postoperative refractive shifts occur [23, 28]; however, no consensus has been reached on their underlying mechanisms. After cataract surgery, a hyperopic shift has often been reported in PACG patients due to the shallower anterior eye chambers and shorter AL. However, few studies have sought to investigate refractive shifts in patients with different AL. Our results showed an increased incidence of hyperopia after Phaco-IOL-GSL, especially in patients with normal axial length. Further studies involving a larger number of cases could reveal other factors that can influence refractive shift.
In addition, visual field examination showed that the PSD, MD, and VFI improved in the short axial group after surgery but no statistically significant in the normal axial group. This finding may be accounted for by the varying degree of severity of cataracts in the two groups. By conducting visual field evaluation in patients with glaucoma after cataract surgery, Zhao et al. found a significant increase in mean visual field sensitivity; however, the difference in the severity and distribution of visual field defects at baseline led to differences in the improvement in visual fields after cataract surgery . Besides, a decrease in the use of postoperative antiglaucoma medications was found. The success rate of Phaco-IOL-GSL has been reported to be 80–100% [30, 31]. In our study, the success rate at the last follow-up was 95.2%, including the complete success of 48.19% and qualified success of 46.99%. However, four unsuccessful cases were found in our study that were managed with a drainage valve or by implantation of an EXPRESS filtration device. The uncontrollable IOP may be accounted for the PAS recurring. Moreover, prolonged uncontrolled IOP accompanied with chronic inflammation of the trabecular meshwork also disrupted the normal function of the trabecular meshwork.
The limitations of our study are the lack of cases with AL > 24.5 mm. It remains uncertain whether the same changes found in our study would occur in this particular patient population. The sample size of each group was small and we did not consider confounding factors that may affect the postoperative refractive outcome, including the formula for calculating IOL power, surgical technique, and IOL material. Our study also lacked some dynamic observations of postoperative indicators, like corneal high-order aberrations and manifest refraction. Studies with larger sample sizes are required to further explore the mechanisms underlying changes in corneal high-order aberrations and refractive errors after surgery in PAC or PACG with concomitant cataract patients with different AL.