Traditional surgical treatments to destroy the ciliary body, like cyclocryotherapy and cycloodiathermy, deliver the energy in a non-focused form, and that’s why they are non-selectivity and may lead to various adverse reactions. Another method called cyclophotocoagulation delivers focused energy to the eye, but the destroy degree depend on the absorption of the optical energy, which can be influenced by tissue pigmentation. HIFU, unlike optical energy, can be focused to the selected location without being absorbed by the tissues. So the treatment modality ultrasound cyclo plasty using HIFU to cure glaucoma can cause very limited damage to adjacent tissue. With the increasing application of EyeOP1 in clinical, more and more studies have demonstrated this treatment modality has excellent safety and effectiveness in reducing intraocular pressure, and even has some effect in refractory glaucoma patients [8–10, 18, 19]. It means that this technology will probably be used more widely in the future. With the continuous promotion of UCP surgery, it is urgent to conduct research on the UCP probe model distribution to guide clinical decision-making and UCP probe design.
Among the probes suitable for patients who need UCP surgery in China, Model 12 probe accounts for the vast majority, with a proportion of 69.05%, which exceeds the proportion of the other two probe models combined. Model 13 is second, accounting for 26.65%, and Model 11 is far less than the other two with a proportion of only 3.35%. NA means all these three models don’t adapt to their eyes, with a percentage of 0.95%. For patients with POAG and congenital glaucoma, Model 13 accounts for a higher proportion, which is 52.50% and 100%. There are only 4 congenital glaucoma patients with 6 eyes in this study, so the sample size may be not enough to effectively estimate the overall level. Among all eyes using the Model 13 probe, eyes of POAG patients accounted for the highest proportion (45.22%), although PACG patients outnumber POAG patients. Moreover, Model 13 probe accounts for 52.50% among all eyes with POAG, exceeding the other two probes. The probe model is calculated by nomogram with AL and WTW as parameters and the size of the probe model is proportional to AL and WTW. These observations suggest that POAG patients tend to have longer AL, which is consistent with some studies on the axis length of POAG patients. A study conducted by Mieko showed that AL tended to increase as patients with POAG progressed. In contrast, Model 12 probe accounts for the highest proportion among PACG patients. The proportions of Model 12 probe are 81.16%, 77.06% among all probe models in APACG and CPACG patients, respectively. Moreover, among all the eyes using the Model 12 probe, 70.67% of them are eyes of PACG patients. This result indicates that PACG patients tend to have shorter AL. This is consistent with the results of many studies on the axial length of PACG patients[21–23].
In this study, PACG patients, POAG patients and SG patients accounted for 58.00%, 21.08% and 8.12% in all the patients, respectively. According to a systematic review of the prevalence of glaucoma in China, in 2015, the prevalence of POAG, PACG and SG patients in China were 5.22%, 7.14% and 0.76%, respectively. Compared with the statistical results, the consistent conclusion is that the proportion of PACG patients was the highest in this study, followed by POAG patients and SG patients. However, in this study, the proportion of PACG patients was significantly higher than the population. This may be related to the fact that POAG patients choose more medical treatment than surgical treatment, resulting in fewer POAG patients and more PACG patients participating in this study.
Eyes without a suitable model accounted for 0.95% of all eyes, which means that these three types of probes have excellent applicability in Chinese glaucoma patients. Of all the 19 eyes that have no suitable probe model, 26.31% is because of too short WTW (shorter than 10mm), 36.84% is because of too long WTW (longer than 13mm) and 36.84% is because of mismatched AL and WTW. Too long or too short WTW could result that the energy of the probe cannot be effectively focused on the corresponding part of the ciliary body. Even though the length of WTW is within the normal range, when an eye has a long WTW and a too short AL or a short WTW and a long AL, it could result in a difference in the shape of the ciliary body, making the energy focused ineffectively. Therefore, we concluded that the main parameter that mainly affects whether the patient’s eye can have a suitable model is WTW, followed by the consistency of AL and WTW. The mean WTW of the participants in this study is 11.55 ± 0.50mm. It is very close to the result of an investigation on the evaluation of WTW based on a large sample of Chinese cataract patients, in which the mean WTW is 11.69 ± 0.46mm. The verification and analyze of WTW and AL data need to be carried out more in the Chinese glaucoma patient population, though related studies are rare.
As far as we know, this is the first study aimed at the distribution of the probe model of UCP. Despite the sufficient sample size, this study may still be not enough representative of the entire population. This study is a clinical-based cross-sectional study, so the results need to be further documented in community-based epidemiologic survey. But it needs gathering a large number of patients who require surgery and accept ophthalmic testing, which well be a tough challenge.
In conclusion, the present study provides previously unavailable information concerning the patient demographics and distribution of UCP probe model in Chinese glaucoma patients. This study may help surgeons make appropriate decision about UCP probe choices and may assist in the design of new device to execute UCP surgery. Our results need to be confirmed by a larger sample of data in a wider area.