The information of the long term surgical outcomes in severe and end stage glaucoma with controlled IOP is scarce. Particularly, the understanding on the visual outcome of these patients after cataract surgery is lacking. The reported surgical outcomes of cataract surgery in severe and end stage glaucoma in literature were mainly come up from patients who were medically uncontrolled [9, 21]. In glaucoma patients with controlled IOP, cataract surgery is seldomly performed since they are at high risk of “wipe out” [6, 7]. Here, our present retrospective study instead shows that the postoperative VA of PACG patients significantly improved after cataract surgery. In addition, the number of glaucoma medications also significantly reduced. Moreover, the baseline MD, VFI and glaucoma stage may help to predict the visual outcome after surgery.
Cataract extraction was reported to improve the VA in glaucoma patients with most of them were in the early stage or medically uncontrolled. For instance, in the Collaborative Initial Glaucoma Treatment Study (CIGTS), the VA was improved abruptly after cataract extraction and maintained for 1.5 years in glaucoma with preoperative mean deviation of -5.74dB [22]. And in 2018, Igor et al. reported that the VA of severe and end stage glaucoma patients was not improved when combined the glaucoma surgery of NPDS with phacoemulsification [23]. While in his later study, the VA was improved after the same surgeries [9]. Both of the studies were last for 6 months. The difference in conclusion may be due to the difference in sample sizes, with only 5 in the earlier one study and then increased to 18 eyes for the later. Even in these medically uncontrolled eyes, VA can be improved after cataract surgery although the primary purpose was to reduce IOP. We hence speculated that cataract extraction can also improve VA in IOP controlled eyes after surgery in these severe and end stage glaucoma. In clinical settings, IOP is always the primary focus in glaucoma management while VA is rarely considered as an assessment parameter of treatment outcome in glaucoma patients. However, VA is highly reflecting the life quality of patients. For glaucoma patients in the severe and end stage with constricted visual field, VA indeed reflects more about the subject perception and the ability to interact with environment [10]. Accordingly, VA improvement in these patients offer an important opportunity to improve their quality of life. Here, we pioneeringly provided the information that the mean VA improved from 0.69 ± 0.55 to 0.46 ± 0.52 logMAR unit with a mean follow up of 21.89 ± 7.85 months, in IOP controlled severe and end stage PACG patients. This result is encouraging and useful since little is known about the visual outcome of severe and end stage glaucoma patients with IOP controlled before. It is difficult to quantify the vision reduction contributed by cataract or glaucoma independently but based on this study we can now suggest VA can be improved in these patients after cataract surgery.
The reason that cataract surgery was seldom performed solely for the purpose of visual improvement in severe and end stage glaucoma patients with controlled IOP, is due to the risk of “wipe out”. It is a long-standing debate whether cataract surgery should be performed on patients with severe and end stage glaucoma. In the past, the reported incidence of “wipe out” in end stage glaucoma was discrepant. Some suggest this to be a rare or even non-existent complication and others fear the risk of sudden visual loss [6, 21, 24]. In our study, no cases of “wipe out” occurred. Most of the studies that reported high rate of “wipe out” were more than 26 years ago. Nowadays, with the advanced technologies, complications can be well resolved and “wipe out” might have a chance to be relegated to a place in history [25]. “Wipe out” was regarded as a sudden vision loss without apparent causes especially in advanced glaucoma after filtering surgery [6, 7], and was suspected to be related with ocular hypotony during surgery. In this study, all the surgeries were performed by a single experienced glaucoma specialist, no cases of “wipe out” was observed and 84.2% eyes showed better or maintained VA at the final visit. These results therefore supported that cataract surgery in general is safe and effective on patients with severe and end stage glaucoma patients. For the eyes with postoperative complications, 2 eyes had PCO and were managed by posterior capsulectomy and their final VA were improved. Malignant glaucoma occurred in one eye and shallow anterior chamber happened in another eye. Both showed unchanged VA in the final checking. In addition, from our linear regression analysis, the greater baseline MD, higher VFI and lower glaucoma stage may predict better VA after cataract surgery. However, VA is not directly related to the visual field. The functional visual acuity (FVA) measured by an AS-28 FVA measurement system had shown a weak correlation with MD in glaucoma with different severities [26]. Here, we hypothesize that the VA may be more associated with visual filed parameters in severely damaged glaucoma. To our knowledge, the visual field parameters and glaucoma stage have not been indicated as the predictive factors of the VA outcomes in severe and end stage glaucoma after cataract surgery. These factors may provide an important reference to the decision management of treatments for these patients.
Traditionally, in PACG, the surgical methods were compared between the PEI alone and combined phacotrabeculectomy. It was proved that combined phacotrabeculectomy was more effective in IOP lowering than PEI alone irrespective baseline IOP control. However, it had more postoperative complications (8 complications vs 0 complication) like “wipe out”, ocular hypotony and poor IOP control [17, 27]. Compared with trabeculectomy, GSL was reported to be safe with mild complications including intraoperative hyphema, mild zonulysis and postoperative IOP spikes [28, 29]. Medically uncontrolled glaucomatous eyes warrant surgeries to decease IOP since elevated IOP increases the risk of glaucoma progression. In medically controlled eyes, especially in the patients with constrict visual field, balancing the risk and benefit of surgery should be more careful. And GSL is more suitable than traditional procedure like trabeculectomy for patients with severely damaged optic nerve.
In the present study, 17 eyes underwent combined PEI-GSL and only 2 eyes received PEI alone since in the perioperative examination, PAS was not found in these 2 eyes. PEI alone was reported to sufficiently reduce the IOP in PACG and whether GSL should be combined was controversial in previous studies [29, 30]. The mechanism that PEI decreasing the IOP in PACG is that lens extraction can partly relieves the role of anteriorly positioned lens in the PACG by implanting a much thinner IOL. And PEI itself may mechanically open some PAS by the use of viscoelastic during procedure. The various effects of GSL may be due to the differed PAS, study population and short follow up duration. In the most recent one randomized clinical trial, GSL did not show additional IOP lowering effect over PEI alone[29]. However, the subgroups of Singapore and Vietnam displayed opposite results of the two surgical procedures. And this may be the reason that the final result did not demonstrate a significant difference between PEI and PEI-GSL. In addition, at 12 months after surgery, the PAS in the PEI-GSL was slight less than in the PEI in the Husain’s study[29]. This may indicate that combined with GSL may warrant a longer time for angle open in PACG which in turn will benefit the IOP maintainance. Hence, in our study, although the IOP was normal preoperatively, GSL was still performed in eyes with PAS. It is said higher baseline IOP resulted greater IOP reduction [29]. In this study, the preoperative IOP was all under 21mmHg with a mean IOP of 13.8 ± 3.3 mmHg. And there was no significant change after surgery with a mean postoperative IOP of 13.2 ± 3.9 mmHg. Nevertheless, it can be noticed that percentage of eyes with IOP above 15 mmHg reduced from 52.6% at baseline to 31.6% at the final visit. And it can also be revealed on the other hand, the IOP control after cataract extraction was demonstrated by the decrease of topical glaucoma drugs used in the postoperative period. The number of glaucoma medications were significantly reduced. Also, the percentage of patients who came off topical glaucoma drugs was greatly increased from 21.1% to 78.9%. It would be meaningful to investigate how such reduction of the drugs impacts on the quality of life of patients, financial costs and adverse effect from the drugs.
Since this is a retrospective study, we mainly used the VA as the indicator of the success of cataract surgery. Other measures like subjective visual function, color perception and overall satisfaction to surgery were not documented. They may also be important parameters to evaluate the quality of life of patients. Also, due to the limited sample size and follow up duration, the current dataset is insufficient to analyze the significance of glaucomatous progression and related complications. A larger sample size of prospective study is needed for further justifications.
In conclusion, cataract extraction provides an additional opportunity of VA improvement in severe and end stage glaucoma patients with controlled IOP. It may also relief the life burden of patients by reducing or even coming off their topical medications. The prediction of VA outcome can refer to the preoperative visual field parameters including MD, VFI and glaucoma stage. The results from our study may change the traditional management practice of severe and end stage glaucoma with controlled IOP and greatly improve the quality of life of patients.