Re-formation of absent anterior chamber by iris incision using a 20-gauge knife in eyes with advanced paediatric vitreoretinopathies

Background To present the novel usage of iris incision in paediatric patients lacking an anterior chamber due to various advanced vitreoretinopathies. Methods Forty-one patients (41 eyes) were enrolled in this consecutive, prospective study. Iris incision was performed in all patients. The number of iris incision times, surgical procedures, and intraoperative and postoperative complications were collected. Patients were followed up for at least 6 months. Results Anterior chamber formation was achieved with only 1 initial episode of iris incision in 28 (68.3%) eyes, with 2 episodes in 11 (26.8%) eyes, and with 3 episodes in the remaining 2 (4.9%) eyes, which also underwent 1 episode of external SRF drainage. Except for iris incarceration, which occurred in 7 (17%) of the eyes during surgery, no other related complications were noted at the last follow-up. Conclusions This novel use of iris incision is effective, simple and safe in the management of an lost anterior chamber.

anterior chamber (AC). If left untreated, this can cause many complications, such as secondary glaucoma, corneal degeneration, or even phthisis bulbi. To avoid these complications, lensectomy with or without vitrectomy is recommended. However, while AC formation is challenging, it is required for further manoeuvres. Traditionally, external drainage of subretinal fluid (SRF) could be indicated to achieve AC formation in cases with flat AC secondary to an advanced paediatric vitreoretinopathy. [3][4][5] However, external drainage is associated with complications, such as retinal incarceration, subretinal haemorrhage, and loss of vitreous. [6,7] Additionally, some sight-threatening complications have been associated with SRF drainage; these include subretinal haemorrhage, retinal incarceration, and iatrogenic retinal holes. [8,9] The author's personal experience suggests that a sudden rapid outflow of SRF may also lead to iridodialysis. In addition, a constant flow of SRF could decrease the definition of the surgical field. These disadvantages associated with the external drainage of SRF demonstrate that more effective and safer techniques are needed to support the management of absent AC in paediatric patients with advanced vitreoretinopathies. To resolve these issues, we performed iris incision instead of external drainage of SRF in paediatric patients with absent AC.
Over the past few years, paediatric patients with absent AC caused by various advanced vitreoretinopathies have been referred to the authors' clinical centre. In this study, we describe the novel usage of iris incision in these paediatric patients.

Patients and Methods
This study adhered to the tenets of the Declaration of Helsinki and was approved by the institutional review board of Tianjin Medical University Eye Hospital. Informed written consent was obtained from the parents or guardians of each participant because they were all under-aged children. This study is a consecutive, prospective, interventional case series.

Patients
Forty-one patients (41 eyes) with absent AC resulting from advance vitreoretinopathy (including 30 eyes with FEVR, 6 with PHPV, and 5 with ROP) were collected in the present study between January 2016 and October 2017. In this study, the AC completely disappeared in all patients with intraocular pressure ranging from 19 to 59 years old. All  (Fig. 1D). If AC formation could not be achieved with the assistance of Healon after one episode of iris incision, a second or third iris incision was performed.
The procedure was combined with external drainage of SRF if AC formation failed after three episodes of iris incision. In the current study, a combination procedure including SRF drainage was performed in two (4.8%) patients. In these two patients, the SRF was drained trans-sclerally using a penetrating needle (27-gauge needle) near the position on the equator overlying the portion of detached retina with the greatest retinal detachment height. After an AC was formed with the assistance of Healon, an infusion cannula connected to a balanced salt plus solution (Alcon, Laboratories, Inc) was injected into the AC through a corneal incision followed by lensectomy with or without vitrectomy. If posterior iris synechia was found, Healon was used to separate the iris from the lens before lensectomy.

Results
The patients' information is shown in Table 1. There were 18 female and 23 male patients with a mean age of 9.5 ± 7.5 months old. A novel iris incision approach was successfully performed in 41 eyes (41 patients) with total absent AC resulting from advance vitreoretinopathy (including 30 eyes with FEVR, 6 eyes with PHPV, and 5 eyes with ROP).
Typical patients are shown in Fig. 2. AC formation was achieved in 28 (68.3%) eyes treated with only 1 initial episode of iris incision, 11 (26.8%) that required two episodes of iris incision, and 2 that required 3 episodes of iris incision (4.9%), with this last group of patients combined with 1 episode of external SRF drainage.
The clinical characteristics and surgical procedures applied in these procedures are shown in Table 2. A major intraoperative complication of iris incision is iris incarceration, which occurred in 7 (17%) of 41 eyes (Fig. 3). Among these cases, the incarcerated iris was successfully returned to the AC in all 7 eyes. The AC remained deep and stable in all cases. No iris incarceration or other related complications were observed at the last follow-up. All external SRF drainage-related complications are presented in Fig. 4.

Discussion
In the current study, 41 patients (including 30 eyes with FEVR, 6 with PHPV, and 5 with ROP) with a total absence of AC were enrolled. We found that this novel iris incision approach was simple, safe, and effective in supporting the formation of absent AC in a paediatric population with advanced vitreoretinopathies. AC formation was achieved in 95.1% of the eyes after 1 or 2 episodes of iris incision.
Advanced paediatric vitreoretinopathies tend to be more aggressive and to lead to severe complications.
[10] Surgeries for vitreoretinopathies are more challenging in paediatric than in adult patients. In advanced paediatric vitreoretinopathies complicated with total retinal detachment, the disappearance of the AC can be caused when the lens and iris are pushed into a more frontal position. Traditionally, external drainage of SRF could be indicated to achieve AC formation in cases with flat AC. [3,4,6] However, this procedure could be complicated by haemorrhage, incarceration of the retina, and/or vitreous or retinal perforation. [6,7] In addition to these conventional complications, the author's personal experience indicates that the sudden rapid outflow of SRF can also lead to iridodialysis. The constant outflow of SRF can decrease the definition of the surgical field and lead to subconjunctival effusion. Thus, to address these external SRF drainagerelated problems, the authors were inspired by the notion of iridotomy to make creative usage of iris incision to assist in the formation of AC in patients with absent AC due to advanced vitreoretinopathies. In these cases, as the pressure in the posterior chamber was high, the aqueous humour in the posterior chamber could have outflowed through the iris incision site(s), thus reforming the AC for further manoeuvres.
The use of iris incision has several advantages over the use of external drainage of SRF.
First, the use of iris puncture is effective in the formation of AC. In the current study, AC formation was achieved in 95.1% of the eyes that underwent up to 2 episodes of iris incision. Second, the use of iris puncture simplified the surgical procedures and resulted in a shorter total operative time. Third, the site(s) of puncture was (were) chosen according to the requirements of further surgical manoeuvres. Thus, no extra incisions were required. Fourth, there were few related complications. In the current study, only iris incarceration was observed during the surgery, and no related complications were observed in any cases at the last follow-up. Fifth, iris incision, unlike external drainage of SRF, does not affect the surgical visual field. Sixth, this technique is simple to perform and has a short learning curve.
In the current study, AC formation was achieved in 28 (68.3%) eyes with only 1 initial episode of iris incision and in 11 (26.8%) eyes with 2 episodes of iris incision. Only 2 (4.9%) patients needed a combination that included 1 episode of external SRF drainage.
The major intraoperative complication of this iris incision approach was iris incarceration, and the iris was easily returned to the AC. The AC remained deep and stable in all cases.
Our study has limitations. Due to a lack of cooperation, ultrasound biomicroscope was not performed in all patients. However, all patients underwent indirect ophthalmoscopy to detect the condition of the AC. In addition, all surgical procedure were performed by a single surgeon, thus minimizing the effect of surgical procedures.
In conclusion, the creative use of iris incision proposed here was effective, simple and

Consent for publication
The written consent for publication of the individual details and images was obtained from each patient. For patients under 18-year old, the written consent was obtained from his/her parent (s) or legal guardian(s).

Availability of data and materials
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
This study was partially supported by the National Natural Science Foundation of China (No. 816710875), the Natural Science Foundation of Tianjin City (18JCQNJC10700), the Natural Science Foundation of Tianjin City (17JCYBJC27200). The funding body has no role in the design of the study and collection, analysis, and interpretation of data or in writing the manuscript.

Authors' contributions
CL C and T T have designed the study, collected and analyzed the data, wrote the manuscript. PQ Z and XR L designed the study, performed all the treatment and agreed to be accountable for all aspects of the work. All authors read and approved the final manuscript.