The indications for IOL intrascleral fixation included long eye axis (20.3%), PE (18.6%), trouble in surgery (17.8%), history of trauma (16.9%) and so on; however, in 24.6% of cases, surgery was performed for unknown causes. These unknown causes may include causes that were not identified in the interview, but numerous genetic disorders and other causes may have been missed.
In addition, it was observed that 23.7% of cases had overlapping predisposing factors. Among them, the case with both PE and trouble in surgery was one of the most common. It was reported that the prevalence of PE in a Japanese population was 3.4%,13 and it is also known that PE is one of the causes of intraoperative problems during a cataract surgery.14 Therefore, the observation of many cases with both PE and trouble in surgery is convincing. The case with both long eye axis and history of vitrectomy was also one of the most common cases with overlapping predisposing factors. It was reported that the mean eye axial length for the patients with IOL dislocation after lens replacement surgery was 25.6 mm,9 so a history of vitrectomy might be relevant to a long eye axis. On the other hand, considering the previous report that 15.2% of junior high school students in Japan have an eye axis length of 26 mm or longer,15 it seems that the number of persons with long eye axis is much larger than those with the other predisposing factors. However, only 16 of 48 cases with long eye axis had no other predisposing factor. This result suggests that a patient with long eye axis complicated by the other predisposing factor may tend to undergo IOL intrascleral fixation more often than with long eye axis alone, even though a patient with only long eye axis may necessitate IOL intrascleral fixation.
In total, there were more than twice as many male cases as female cases. In contrast, males were more than three times as many compared to women in the history of trauma, atopic dermatitis, and vitrectomy groups. In Japan, the number of male patients with rhegmatogenous retinal detachment is approximately twice that of female patients. 16 In this study, the number of male patients was also higher than that of female patients. It is believed that males are more active than females and therefore suffer more trauma. Although atopic dermatitis is more common in females than in males,17 more males had atopic dermatitis than females in this study. Although the number of patients with RP in Japan is not sex-dependent18; in this study, RP was more common in females. However, the results of this study cannot be considered definitive due to the small sample size.
In the cases of lens deviation, anterior and fall into vitreous cavity are most often seen. On the other hand, downward and fall into vitreous cavity are most popular in the case of IOL deviation. Lens dislocation in Marfan syndrome is usually bilateral and most often occurs in the superotemporal direction, although other directions are not uncommon.19,20 Downward deviation and fall into vitreous cavity were more common in this study, and it is most likely that the weight of the lens placed strain on the superior ciliary zonule throughout life. In addition, regarding IOL deviation after pars plana vitrectomy, it has been suggested that extensive peripheral vitrectomy probably damages the zonular fibers and resulted in the dislocation of the IOL.9 The reason why there are many aphakia cases with PE or trouble in surgery is that they were referred to our clinic after cataract surgery performed at other hospitals, and intraoperative problems prevented IOL insertion. In the trauma cases, the direction of deviation also varied, perhaps because of the various directions of impact.
In this study, we found that IOP decreased in the short term (1 month postoperatively) compared to the preoperative period as a whole. Cases with upward and anterior deviation of the lens, IOL fall into the vitreous cavity, and downward deviation of the IOL demonstrated significant decrease in IOP after surgery, whereas there were no significant differences between the preoperative and postoperative IOPs in cases with aphakic eyes and no dislocation. Crystalline lenses and IOL dislocation in chambers may be linked to hypertension, which can be attributed to two main factors: circulatory disturbances of the aqueous humor and inflammation. Abnormalities in the position of the lens and IOL may cause retention of aqueous humor, which may inhibit smooth circulation and increase IOP. In particular, a significantly high preoperative IOP was observed in the cases with anterior lens deviation of this study and surgery resulted in good IOP reduction. Cases with anterior lens deviation are prone to IOP elevation due to pupillary block. In fact, it has been reported that lens subluxation is often misdiagnosed as angle closure glaucoma.21
Residual lens material in the eye is also known to cause high IOP. The first is phacolytic glaucoma, which occurs when the lens protein itself and the macrophages that phagocytose it obstruct the outflow of aqueous humor.22 The other is phacoanaphylactic glaucoma, which is secondary to lens-induced uveitis, caused by an immune response to lens proteins.23 In some cases, including those with intraoperative cataract problems, there may have been residual lens material in the eye, causing the inflammation described above and elevated IOP.
The observations of significant differences between preoperative and postoperative IOPs in history of vitrectomy and long eye axis groups might be due to many cases of vitreous cavity and downward deviation in these groups, whereas many cases of aphakia and no deviation might result in no significant IOP change in PE or trouble in surgery groups. After excluding the cases with overlapping of predisposing factors, the decreases of postoperative IOP in history of vitrectomy or long eye axis groups are not remarkable due to the small sample sizes. The cases with history of trauma showed significant differences in IOP before and after surgery, and most of the cases had lens dislocations in various directions (not necessarily aphakia or no deviation). These results support the idea that the presence of intraocular residues influences the increase in IOP.
We were able to examine eye drop score in about 70% of the cases in this study, and in almost all cases eye drop score was zero both preoperatively and postoperatively. We believe that the influence of eye drop score is not so strong.
It should be noted that IOL intrascleral fixation does not lower IOP; rather, patients who require IOL intrascleral fixation are likely to have elevated IOP for some background reasons, and intrascleral fixation is not recommended for lowering IOP. The effectiveness of combined treatments such as IOL fixation plus the implantation of the Ahmed glaucoma drainage device has also been reported for treating ocular hypertension in conjunction with IOL fixation.24 Trauma-induced ocular hypertension has also been investigated through various mechanisms.25 When deciding on a surgical procedure, it is necessary to carefully examine whether surgery improves symptoms.
The limitations of this study are as follows. First, the day after surgery, IOP was measured in the ward with GAT; however, in the outpatient setting, GAT and NCT were mixed and were not measured by a single examiner. However, GAT and NCT are thought to be correlated.26,27 Second, long-term changes and the development of complications were not included in this study. In many cases, patients referred for IOL intrascleral fixation were then referred back to the original institution relatively early after surgery; therefore, long-term follow-up was not available.