Pure ICL Implantation: A Novel Ophthalmic Viscosurgical Device-Free Technique

doi:10.21203/rs.3.rs-150626/v1

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Pure ICL Implantation: A Novel Ophthalmic Viscosurgical Device-Free Technique

https://doi.org/10.21203/rs.3.rs-150626/v1

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Background: To assess the clinical efficiency of a novel ophthalmic viscosurgical device-free (OVD-free) method for intraocular collamer lens (EVO-ICL) implantation in myopic eyes.

Methods: In this retrospective cohort study, 40 eyes underwent standard ICL implantation, and 40 eyes underwent OVD-free (Pure) ICL implantation. Preoperative and postoperative uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (BCVA), equivalent spherical degree (SE), intraocular pressure (IOP), visual quality index, subjective visual quality scale, corneal endothelial cell density (ECD), operation time, and complications were compared between and within the standard and pure ICL implantation groups.

Results: Increased IOP > 22 mmHg 2 h after surgery was noted in 19 eyes (47.5%) in the standard group, but not in the pure group (0%, P < 0.001). Increased IOP relative to baseline was significantly higher at 2 h and 1 day after surgery for the standard group compared with the pure group (P < 0.001). LogMAR UDVA and LogMAR BCVA were significantly improved in the pure group compared with those in the standard group 1 day (P < 0.001) and 1 week (P < 0.001) after implantation, but not after 3 months (P = 0.747 and P = 1.000, respectively). SE was significantly lower in the pure group than in the standard group 1 day after implantation (P = 0.003). No significant differences in SE were observed at any time point between groups (P = 0.285, P = 0.460). Optical Quality Analysis System (OQAS) II visual quality indicators, such as the modulation transfer function cut-off frequency (MTF cut-off), Strehl ratio (SR), and OQAS under different contrast values [OQAS values (OVs) 20], were significantly better in the pure group than in the standard group 1 day after implantation (P = 0.013, P = 0.009, and P = 0.004, respectively). SR, OV20%, and OV9% were significantly better in the pure group than in the standard group 1 week after implantation (P = 0.003, P = 0.047, and P = 0.002, respectively). No significant difference in ECD changes within or between groups was observed (P > 0.05). The operation time for the pure group (2.897 ± 0.346 min) was significantly shorter than that for the standard group (4.444 ± 0.656 min; P < 0.001). No complications were reported for either group during the observation period, except early IOP elevation in the standard group.

Conclusions: The pure ICL implantation method was associated with faster visual acuity recovery, a shorter operation time, and more stable intraocular pressure. Pure ICL represents a safe and convenient method for ICL implantation compared with the standard method, completely eliminating OVD-related complications without causing additional complications.

Ophthalmology

Pure ICL implantation

intraocular pressure

visual quality

Myopia describes the condition in which the refractive system of the human eye focuses parallel light in front of the retina in the relaxed state^[1]. In China, approximately 700 million people suffer from myopia, and 10% of those suffer from high myopia. Various surgical methods can be used to treat myopia, including posterior chamber phakic intraocular lens (PIOL) implantation, small incision lenticule extraction (SMILE), and laser-assisted in situ keratomileusis (LASIK); however, the surgical options for high myopia patients with limited corneal thickness remain limited to lens replacement and PIOL implantation.

Visian ICL^TM(STAAR Surgical, Nidau, Switzerland) is a type of posterior chamber PIOL^[2-3], and previous studies have shown that EVO-ICL (an implantable collamer lens with a centre hole) implantation is satisfactorily safe^[4]. EVO-ICL implantation can reduce the induction of high-order aberrations and improve contrast sensitivity^[5]. Because the intraocular position of EVO-ICL is close to the eyeball node, magnification approaches 1, and the imaging size of external objects on the retina is similar to that for emmetropia, resulting in EVO-ICL implantation patients presenting better visual quality than patients who undergo corneal refractive surgery. Features such as good postoperative visual acuity, visual quality, and reversibility, have made EVO-ICL the first-line choice for an increasing number of patients with high myopia ^[6-12].

Standard ICL implantation requires ophthalmic viscosurgical device (OVD) injection into the ICL implant container and the anterior chamber (AC) to maintain the operating space and protect the corneal endothelium and lens. Failure to completely clear OVD postoperatively can result in an acute increase in intraocular pressure (IOP) at the early postoperative stage^[13-16]. Intraoperative OVD use may also increase the costs and time required for surgery^[17]. Prolonged surgery and OVD irrigation using a syringe-coupled injection needle may increase the likelihood of contact between the ICL and the transparent lens, leading to early lens opacity after operation^{[18, 19]}. The viscosity and electrostatic charge of OVD materials may result in the suspension of inflammatory cells in the AC, increasing the probability of postoperative inflammatory reactions. To address the adverse effects associated with OVD use, we developed a technology that uses a continuous infusion of balanced salt solution (BSS) through a side-port, completely eliminating the need for OVDs during ICL implantation. We named this technique "pure ICL implantation." In the present study, the double-pass technique (using OQAS™ II, Optical Analysis System, Visiometrics, Spain) was used to assess optical quality indicators and intraocular objective scattering index (OSI) in patients who underwent either pure or standard ICL implantations. The National Eye Institute Refractive Error Quality of Life Instrument-42 (NEI-RQL-42) score was used to evaluate the subjective visual perceptions of the patients. The IOP, uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (BCVA), equivalent spherical lens (SE), corneal endothelial cell density (ECD), operation time, and complications were also examined. The results of this study provided additional information regarding the safety and effectiveness of pure ICL implantation, providing a basis for the clinical popularisation of this technique.

Patients

A total of 80 eyes in 40 patients (18 men and 22 women) who underwent EVO ICL implantation at Nanjing Drum Tower Hospital, affiliated with Nanjing University Medical School, from 2015 to 2020 were retrospective included in this study. Standard ICL implantation was performed in 40 eyes, and pure ICL implantation was performed in the other 40 eyes. Patients with a history of eye surgery, severe dry eye, progressive corneal degeneration, cataracts, retinal detachment, or uveitis were excluded. The institutional review board at Nanjing Drum Tower Hospital approved this study, which was performed in accordance with the tenets of the Declaration of Helsinki. All patients signed informed consent concerning the risks of surgery.

Observation and detection indicators

Routine preoperative examinations were performed for all eyes, including UDVA, BCVA, scotopic pupil size, anterior segment examination under slit lamp microscope, and retina examination, using three-mirror contact lenses. Optometry with performed using a CV-3000 comprehensive optometry testing machine (TOPCON company, Japan), including cycloplegic refraction and subjective optometry. The AC depth and corneal curvature were measured using an OCULYZERII (WaveLight, Alcon). A panoramic ultrasound biomicroscope (UBM) was used to study the anterior segment structures of the eye and measure the sulcus-to-sulcus (STS) distance, which was used to determine the ICL size. We calculated the ideal ICL size as STS + 0.7 mm. The IOP was measured using a non-contact tonometer (Topcon Company, Japan), both before and after surgery. Modulation transfer frequency (MTF), Strehl ratio (SR), three Optical Quality Analysis System (OQAS) contrast values (OV100%, OV20%, and OV9%), and objective scattering index (OSI) were detected by OQAS Ⅱ. The ECD was measured using an ST.3000P corneal endothelial cell counter (Topcon Company, Japan). National Eye Institute–Refractive Error Quality of Life Instrument–42 (NEI–RQL–42) scores were collected before and 3 months after surgery. The time of each surgery was recorded. Before the operation, 0.5% levofloxacin eye drops (Santen, Japan) were administered for 3 days to prevent infection, and 0.1% flumilone eye drops (Santen, Japan) and 0.5% levofloxacin eye drops were administered 4 times a day for 2 weeks after the operation. Pranoprofen eye drops were also administered 3 times a day for 1 month after operation. In this study, the same doctor was in charge of all surgeries.

Anterior chamber maintainer (ACM)

The anterior chamber maintainer (ACM), featuring a 0.4 mm diameter and 2 mm length, was designed by our group and produced by an ophthalmic instrument company. The head was bevelled at a small angle (60 degrees)to facilitate access into the AC through the side incision (Figure 1).

Surgical procedures

Standard ICL implantation

Before surgery, the eyes were treated with compound tropicamide eye drops (Santen, Japan) 4 times to expand the pupil diameter to greater than 7 mm. Obuvacaine hydrochloride (Santen, Japan) eye drops were applied 4 times as topical anaesthesia. A small OVD quantity (1.7% sodium hyaluronate, Shandong Bausch & Lomb Freda Company) and balanced salt solution (BSS, Alcon, USA) were injected into the ICL implant container. The injector was properly installed and placed in BSS for later use. An assisted right-side incision was made, through which an appropriate OVD quantity was injected into the AC. A 3.0-mm transparent corneal main incision was made, typically placed on the steep axis of corneal curvature, to release corneal astigmatism. The ICL was inserted from the main incision into AC, and a sufficient OVD quantity was injected into the front surface of the ICL to maintain the operating space. After gently tucking the footplates beneath the iris and adjusting the ICL to a central position, the OVD was manually irrigated from the AC using BSS in an injection needle attached to a syringe. Finally, the incisions were made watertight.

Pure ICL implantation

Before surgery, the eyes were treated with compound tropicamide eye drops 4 times to expand the pupil diameter to greater than 7 mm. Obuvacaine hydrochloride eye drops were applied 4 times as topical anaesthesia. The ICL implant container was filled with BSS, and the ICL injector was installed properly and placed in BSS for later use. Symmetrical assisted incisions were made on the right and left sides, approximately 0.4 mm wide, and the ACM was placed in the left incision. A 3.0-mm transparent corneal main incision was performed, typically located on the steep axis of corneal curvature, to release corneal astigmatism. The ICL was inserted from the main incision into AC, gently tucking the footplates beneath the iris and adjusting the ICL to a central position. Finally, the incisions were made watertight (Video 1).

Management of early acute IOP elevation

Early acute IOP elevation was defined as an increase in IOP > 22 mmHg within 2 h after surgery. If early acute IOP elevation was detected, a slit lamp examination was performed to eliminate pupil block or malignant glaucoma caused by excessive vault. If IOP was only slightly elevated (IOP < 25 mmHg), close observation was performed. For moderately elevated IOP (IOP = 25–30 mmHg), topical anti-glaucoma medications were administered. For significantly elevated IOP (IOP > 30 mmHg), AC drainage was performed once through the side incision, with or without the administration of topical anti-glaucoma medication, to reduce IOP to 10–13 mmHg. After treatment, IOP was measured every 2 h until a normal value was achieved.

Statistical analysis

Collected data were entered into Microsoft Excel (Microsoft Co. WA, USA) and analysed using Statistical Package for the Social Sciences (SPSS, version 20; IBM Inc., Armonk, USA). Descriptive and inferential statistical analyses were performed. At the descriptive level, continuous parameters were evaluated for parameter normality and are reported as the mean ± standard deviation (SD). At the inferential level, an independent t-test, a paired-sample t-test, the Mann–Whitney U test, and one-way analysis of variance (ANOVA) were performed. A P-value of less than 0.05 was considered significant.

General data

No significant differences in age, gender, or preoperative SE, UDVA, or BCVA were identified between the two treatment groups (Table 1).

Comparison of IOP between two groups

Preoperative IOP was within the normal range for both groups with no significant difference (P = 0.730). A significant difference in the time course of IOP changes was observed between the two groups. At 2 h post-operation, no patients in the pure group (0%) had IOP > 22 mmHg compared with 19 patients in the standard group (47.5%). One patient in the standard group experienced mild eye pain and corneal oedema, with an IOP of 31 mmHg 2 h post-operation. After performing AC drainage and administering carteolol hydrochloride drops twice, the symptoms disappeared within 24 h, and IOP decreased to 18 mmHg. One day after the operation, both groups presented IOP < 22 mmHg.

At 2 h and 1 day after surgery, the IOPs in the pure group were significantly lower than those in the standard group (P < 0.001). At 1 week and 3 months after the operation, no significant differences in IOP were observed between groups (P = 0.845 and P = 0.687, respectively, Figure 2).

A significant difference in IOP was observed before and 2-h post-surgery in the pure group (P < 0.001), but no significant differences were observed between other time points. A significant difference in IOP was observed before and 2 h and 1 day after surgery in the standard group (P < 0.001), but no significant differences were observed between other (Figures 3 and 4).

The differences between postoperative and preoperative baseline IOP values in the pure group were 1.82 ± 0.96, −0.32 ± 1.69, 0.15 ± 2.02, and −0.1 ± 1.58 at 2 h, 1 day, 1 week, and 3 months post-surgery, respectively, compared with 8.83 ± 2.29, 2.65 ± 2.59, 0.23 ± 2.01, and −0.17 ± 1.84 in the standard group. The differences between baseline and 2-h and 1-day postoperative IOP values were significantly lower in the pure group than in the standard group (P < 0.001). At 1 week and 3 months after surgery, no significant differences were observed between groups (P = 0.868 and P = 0.845, respectively, Figure 5).

Comparison of visual acuity and refractive power between the pure and standard ICL implantation groups

Table 2 shows the visual acuity and refractive power values of both groups. The intra-group comparisons showed increased UDVA and BCVA values for both groups 3 months after surgery compared with preoperative values. Postoperative SE values were significantly lower than preoperative values (P < 0.001).

At 1 day and 1 week after surgery, the UDVA and BCVA values of the pure group were significantly better than those of the standard group (P < 0.001). No significant differences between groups were observed before and 3 months after surgery.

On postoperative day 1, the SE of the pure group was significantly lower than that of the standard group (P =0.003). No significant difference in SE was observed between groups at the other time points.

Comparison of visual quality between pure and standard ICL implantation groups

Table 3 shows the OQAS II visual quality indicators for patients in the pure group before surgery and 1 day, 1 week, and 3 months after surgery. The MTF cut-off frequencies at 1 day and 1 week after surgery were significantly lower than that before surgery (P < 0.001 and P = 0.014, respectively). The SR value 1 day after surgery was significantly lower than that before surgery (P = 0.025). The OV100% values 1 day and 1 week after surgery (P < 0.001 and P = 0.002, respectively) and the values of OV20% and OV9% 1 day after surgery (P < 0.001 and P < 0.001, respectively) were significantly lower than corresponding preoperative values. No significant differences were observed in other OQAS II visual quality indicators between preoperative and postoperative time points. The OSI values 1 day and 1 week after surgery were higher than that before surgery (P < 0.001), but no significant difference in OSI values was observed between 3 months after surgery and before surgery.

Table 4 shows the OQAS II visual quality indicators for patients in the standard group before surgery and 1 day, 1 week, and 3 months after surgery. The MTF cut-off frequency, SR, OV100%, OV20%, and OV9% values 1 day (P < 0.001, P < 0.001, P < 0.001, P < 0.001 and P < 0.001, respectively) and 1 week ( P = 0.005, P < 0.001, P = 0.003, P < 0.001 and P < 0.001, respectively) after surgery were lower than the corresponding pre-operative values . No significant differences any OQAS II visual quality indicators were observed between before and 3 months after surgery. The OSI values 1 day and 1 week after surgery were significantly higher than that before surgery (P < 0.001, P = 0.003, respectively), but no significant difference in OSI value was observed between before and 3 months after surgery.

Table 5 compares the visual quality values of patients undergoing the two surgical methods. We compared visual quality between the two groups before and 1 day, 1 week, and 3 months after surgery. At 1 day after surgery, the MTF cut-off frequency, SR, and OV20% values of the pure group were significantly higher than those of the standard group (P = 0.013, P = 0.009, and P = 0.004, respectively). One week after surgery, the SR, OV20%, and OV9% values of the pure group were significantly higher than those in the standard group (P = 0.003, P = 0.047, and P = 0.002, respectively). The remaining values did not differ significantly at any time point.

NEI–RQL–42 scores

Patients filled out the NEI–RQL–42 before and 3 months after surgery and scored as described by the instructions: the average value of each item = the sum of all points per item/the number of questions per item.

Table 6 shows the within-groups comparisons in NEI-RQL-42 scores between before and 3 months after surgery. At 3 months after surgery, except for a decrease in glare and no significant increase in near vision, all other indicators were significantly higher than those before surgery (P < 0.05) for both groups.

Table 7 shows the between-groups comparison in NEI-RQL-42 scores before and 3 months after surgery. No significant differences in scores were observed between the two groups.

Comparison of corneal endothelial cell density before and after operation within and between the pure and standard ICL implantation groups

Table 8 shows no significant differences in corneal ECD between the pure and standard groups either before or three months after surgery (P > 0.05). No significant differences were observed between these two time points within each group (P > 0.05).

Operation time and complications

The mean operation time for the pure group was 2.897 ± 0.346 min, which was significantly shorter than the operation time of 4.444 ± 0.656 min for the standard group (P < 0.001，Figure 6).

The vault measurements for all postoperative eyes in both groups were between 1/2 corneal thickness (CT) and 3/2CT at each time point after surgery. Except for early postoperative IOP elevation in some patients, no serious complications, such as posterior corneal elastic layer detachment, cataract development, pupil block, or pigment dispersion, occurred during the intraoperative or 3-month follow-up periods.

Through the continuous development and improvement in ICL implantation technology, the EVO-ICL implant with a central hole has become the most mainstream surgical method for intraocular refractive surgery, favoured by patients with high myopia and other refractive errors who are not satisfied with or do not qualify for corneal laser surgery^[20]. The safety and efficacy of ICL implantation have been widely recognised^[^{3, 12}^]. During standard ICL implantation procedures, OVDs should be injected into the ICL implant container and the eyes to reduce the potential for damage to the corneal endothelium and transparent lens and to maintain the AC space for surgery. However, residual OVDs have been associated with increased or abnormal IOP, lens opacity, and slow vision recovery^{[13-16,18,19]}. Bluementhal^[21], Tak ^[22], Fatih^[23], Bardoloi^[24]and other researchers have used various ACM devices to avoid the use of OVDs during phacoemulsification cataract extraction or intraocular lens implantation. Pan^[25] introduced ICL implantation with continuous infusion and a single-handed ACM. Its safety and effectiveness have been confirmed. However, the use of Pan’s ACM that requires one hand limits the coordination of activities that require two hands, such as eye movement. We, therefore, developed a hands-free, operationally convenient ACM. Under continuous infusion conditions, the ICL implantation could be performed without the use of OVDs, referred to as pure ICL implantation. This technique reduces the operation time, promotes the early recovery of vision, and is beneficial for controlling increases in IOP and reducing complications associated with residual OVDs. Pure ICL implantation was found to be effective and worthy of clinical application and promotion.

During traditional ICL implantation, the use of OVDs is essential. OVDs function to fill, protect, and lubricate the AC^[2⁶^,²⁷^]. In this study, the pure ICL implantation technique used a continuous BSS infusion through a side port, to completely eliminate the use of OVDs. Therefore, the ICL spreads faster and does not contact the lens or corneal endothelium and the flushing process applied to remove OVDs is no longer necessary, resulting in a shortened operation time to approximately 3 min, which was significantly shorter than the time necessary for the standard technique, greatly reducing the risk of corneal endothelial damage associated with prolonged operation times, reducing material costs, and improving the experience of both patients and doctors.

A large number of studies^[5,14-16,20,²⁸^] have shown that early postoperative IOP elevation is a common complication due to residual OVDs following ICL implantation using standard methods. The intraoperative use of various types of OVDs may also affect IOP recovery. Gonzalez-Lopez^[14] implanted V4c ICL in 100 eyes, among which, 5 eyes experienced increased IOP 3–6 hours after surgery. They hypothesised that residual OVDs (2% hydroxyl propyl methyl cellulose) blocked the trabecular meshwork or the central hole of the ICL, resulting in increased IOP. Almalki^[15] found that in 534 patients after ICL implantation, 58 patients experienced IOP elevation, including 23 patients with IOP elevation on the first day after surgery (the OVD was 1% sodium hyaluronate). Senthil^[16] found that in the patients with high IOP after ICL implantation, 27% of cases were caused by OVD residue (2% hydroxyl propyl methyl cellulose), including 2 cases with pupil block due to OVD residue. Our study showed that on the first day after surgery, significantly more patients (47.5%) in the standard ICL implantation group had IOP > 22 mmHg compared with the pure ICL implantation group (0%). The incidence of IOP elevation on the first day after surgery was slightly higher in the standard ICL implantation group in our study than in previous studies. This discrepancy may be due to the use of a different OVD (1.7% sodium hyaluronate with high viscosity) or the removal of the OVD using a water injection needle and not an irrigation and aspiration instrument. Therefore, the failure to adequately remove the OVD residue may occur more commonly under these conditions than under conditions of coaxial irrigation and aspiration. In addition, we defined IOP elevation as IOP > 22 mmHg at 2 h post-operation, whereas previous studies used IOP ≥ 24 mmHg or postoperative time relaxation as the evaluation criteria, which may have excluded patients with slightly elevated IOP or late IOP peaks.

The differences between the 2-h and 1-day postoperative IOP values and the preoperative baseline IOP values were significantly lower in the pure ICL implantation group than those in the standard ICL implantation group. The IOP values for both groups returned to normal levels at 1 week and 3 months after surgery, with no significant differences between groups or compared with their preoperative baseline IOP values. The results showed that avoiding OVD use was beneficial for controlling early postoperative IOP elevation and promoting the recovery of IOP after surgery.

The evaluation of visual quality after refractive surgery typically includes both objective and subjective detection methods, such as the objective visual quality indicators measured by OQASII, intraocular OSI, and the subjective visual quality scale reported by patients^[²⁹^–3¹^]. In this study, the OQAS^TMII double-pass technique retinal imaging technology was used to analyse the visual quality of the target by collecting data from the 780-nm laser diode light intensity distribution on retinal imaging. The point light source resolution of an optical system is described by the point spread function (PSF). During the analysis of optical imaging quality, the visual quality indicators, including the MTF cut-off frequency, SR, and OVs at various contrast sensitivities (OV9%, OV20%, and OV100%), and the OSI are derived from the PSF. The results of this study showed that the MTF, SR, OV100%, and OV20% values of patients in the pure group 1 day after surgery, and the SR, OV20%, and OV9% values in the pure group 1 week after surgery, were higher than those values in the standard group. These results suggested that the visual quality of patients in the pure group was better than that of patients in the standard group during the early postoperative stage. Correspondingly, the UDVA and CDVA of the pure group 1 week and 1 day after surgery were also higher than those of the standard group. These differences were thought to be related to the higher IOP, the presence of residual OVDs, and longer operation times in the standard group, which caused AC inflammatory responses. No significant differences in objective visual quality indicators and subjective visual quality scale scores were observed between the two groups at 3 months after surgery, which indicated that both groups had good visual quality at 3 months after surgery.

The cornea is an important component of the refractive system of the eye. The maintenance of corneal thickness and transparency depends on the structural and functional integrity of corneal endothelial cells^[3²^,³³^]. The excessive loss of corneal endothelial cells can lead to the decompensation of corneal endothelial cell function, irreversible corneal oedema, and severe damage to visual function^[3⁴^]. Corneal endothelial cells play decisive roles in the maintenance of normal physiological function in corneal tissues and are completely exposed to a non-physiological environment during ICL implantation. Corneal endothelial cells can come into direct contact with perfusion fluid, viscoelastic agents, surgical instruments, and the ICL, making them vulnerable to various factors. In previous EVO-ICL implantation studies using OVDs, Cao^[3⁵^] reported corneal endothelial cell loss rate of approximately 2% at 6 months after surgery. Lisa^[3⁶^] reported a rate of 1.7% at 12 months after surgery. Pan^[2⁵^] found that the rate was approximately 4.6% at 3 months after surgery. In this study, the loss rate of corneal endothelial cells in the pure group was approximately 2%, whereas that in the standard group was approximately 2.3%, at 3 months after surgery. No significant differences were observed before and after surgery for either group. The results showed that the pure group in this study was not associated with additional damage to corneal endothelial cells, with an outcome similar to the use of OVDs. The lack of additional corneal injury caused by continuous BSS perfusion in the pure group may be due to the shorter operation time in the pure group (2.897 ± 0.346 min), which was nearly half that of the standard group. The AC remained stable during the operation, greatly reducing the risk of mechanical injury due to the operation. In addition, the equilibrium liquefaction composition of BSS is similar to that of aqueous humour. BSS is non-cytotoxic with mild properties and can maintain the pH and osmotic pressure of the AC. In addition, in this study, the BSS perfusion time was short, the flow rate was slow, and the perfusion pressure was appropriate. The continuous application of perfusion fluid could remove intraoperative exudates, tissue fragments, and blood clots, effectively reducing the risks of corneal endothelial cell injury and postoperative inflammatory reactions. In this study, no lesions of the transparent lens were observed in either group intraoperatively of 3 months after surgery, which indicated that pure ICL implantation could safely avoid the occurrence of OVD-related complications, such as corneal endothelial cell death and clear lens injury.

This study has some limitations. The observation time was short, the sample size was relatively small, and this was performed as a retrospective study. In the future, we will expand the sample size, extend the observation time, and conduct prospective randomised studies.

In conclusion, the results of this study indicated that the pure ICL implantation method could avoid OVD-related IOP elevation, reducing the necessity and risk of IOP reduction management strategies, including the use of anti-glaucoma drugs and AE discharge. Pure ICL is a safe and reliable method with clinical application value that can reduce the postoperative inflammatory reaction, shorten the operation time, and reduce operating costs.

ICL: Intraocular collamer lens; OV: OQAS Ⅱ values; OSI: Objective scatter index; MTF: Modulation transfer function; UDVA: Uncorrected distance visual acuity; BCVA: Best-corrected distance visual acuity

Acknowledgements

Not applicable

Funding

This work was supported by the Fundamental Research Funds for the Central Universities(0214-14380487). The funding agencies had no role in the design or conduct of this study, including collection, management, analysis or interpretation of the data, preparation, review or approval of the manuscript or in the decision to submit the manuscript for publication.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Authors’contributions

QQ—Design, drafting, data acquisition, analysis and interpretation. LYB—Design, operator. ZFH—Data acquisition and analysis. FFC—Data acquisition, analysis and drafting. DDZ, RYG, SZ, WWZ, YJL—Data acquisition. ZGX—Design, drafting, analysis and interpretation. All authors read and approved the final manuscript.

Ethics approval

The institutional review board at Nanjing Drum Tower Hospital approved this study, which followed the tenets of the Declaration of Helsinki. All patients signed informed consent concerning the risks of surgery.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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Table 1 Preoperative demographics of the eyes undergoing the pure ICL implantation and standard ICL implantation

	pure method	standard method	P value
Age(years)	24.650±3.282 (21, 35 years)	24.750±3.319 (21, 35 years)	P =0.893
Gender	Male: Female=8:12	Male:Female=10:10
Spherical	-11.306±1.314	-11.638±1.431	P =0.284
Equivalent (D)	(-6.25~-9.25)	(-6.25~-9.50)
LogMAR	1.283±0.226(1.6~0.8)	1.230±0.219(1.6~0.8)	P =0.295
UDVA
LogMAR	0.165±0.103(0.3~0)	0.182±0.098(0.3~0)	P =0.439
CDVA

Notes: P = P value of the data statistically compared between the pure ICL implantation group and standard ICL implantation groups. LogMAR = logarithm of the minimal angle of resolution; UDVA = uncorrected distance visual acuity; CDVA = corrected distance visual acuity; D = diopter.

Table 2 Time courses of the visual and refractive outcomes between the pure ICL implantation and standard ICL implantation groups

	Preoperative	Postoperative period			P-value
	Preoperative	1 day	1 week	3 month	P-value
	LogMAR UDVA
pure method	1.283±0.226	0.008±0.066	-0.038±0.067	-0.038±0.067	P₀<0.001*
standard method	1.23±0.219	0.07±0.085	0.013±0.076	-0.042±0.071	P₀<0.001*
P-value	P₁=0.295	P₁=0.000*	P₁=0.002*	P₁=0.747
	LogMAR BCVA
pure method	0.165±0.103	-0.01±0.071	-0.055±0.064	-0.058±0.071	P₀<0.001*
standard method	0.182±0.098	0.048±0.096	-0.01±0.087	-0.058±0.075	P₀<0.001*
P-value	P₁=0.439	P₁=0.003*	P₁=0.010*	P₁=0.345
	spherical equivalent(D)
Pure method	-11.306±1.314	-0.131±0.253	-0.156±0.202	-0.175±0.206	P₀<0.001*
Standard method	-11.638±1.431	0.044±0.259	-0.113±0.16	-0.144±0.169	P₀<0.001*
P-value	P₁=0.284	P₁=0.003*	P₁=0.285	P₁=0.460

Notes: P₀= P-value of the difference between the preoperative and three month values; P₁= P-value of the difference between the pure ICL implantation and standard ICL implantation groups; *P < 0.05 = significant difference. LogMAR = logarithm of the minimal angle of resolution; UDVA = uncorrected distance visual acuity; BCVA = best-corrected distance visual acuity; D = diopter.

Table 3 Time courses of the optical quality parameters after pure ICL implantation

	Preoperative	Postoperative period
	Preoperative	1 day	1 week	3 month
MTF cutoff frequency (cpd)	48.48±5.24	42.91±6.15	45.32±3.60	48.88±3.92
P-value		P_1<0.001*	P₂=0.014*	P₃=0.999
SR	0.25±0.06	0.23±0.04	0.25±0.06	0.26±0.06
P-value		P₁=0.025*	P₂=0.951	P₃=0.614
OV 100%	1.63±0.16	1.43±0.20	1.52±0.15	1.58±0.16
P-value		P_1<0.001*	P₂=0.002*	P₃=0.167
OV 20%	1.26±0.20	1.10±0.14	1.15±0.23	1.27±0.20
P-value		P_1<0.001*	P₂=0.147	P₃=1.000
OV 9%	0.71±0.18	0.57±0.12	0.70±0.14	0.72±0.12
P-value		P_1<0.001*	P₂=1.000	P₃=1.000
OSI P-value	0.41±0.11	0.60±0.16 P_1<0.001*	0.57±0.16 P_2<0.001*	0.43±0.11 P₃=0.945

Notes: P₁= P-value of the difference in the visual quality parameters before surgery and one day after surgery; P₂= P-value of the difference in the visual quality parameters before surgery and one week after surgery; P₃= P-value of the difference in the visual quality parameters before surgery and three months after surgery. *P < 0.05 = significant difference. MTF = modulation transfer function; OSI = objective scattering index; OV = OQAS value.

Table 4 Time courses of the optical quality parameters after standard ICL implantation

	Preoperative	Postoperative period
	Preoperative	1 day	1 week	3 month
MTF cutoff frequency (cpd)	47.82±4.18	39.79±4.78	43.83±4.47	47.97±3.93
P-value		P_1<0.001*	P_2<0.001*	P₃=0.880
SR	0.26±0.05	0.21±0.03	0.22±0.03	0.27±0.05
P-value		P_1<0.001*	P_2<0.001*	P₃=0.998
OV 100%	1.62±0.14	1.36±0.26	1.44±0.28	1.60±0.15
P-value		P_1<0.001*	P₂=0.005*	P₃=0.987
OV 20%	1.23±0.26	1.01±0.15	1.06±0.15	1.18±0.26
P-value		P_1<0.001*	P₂=0.003*	P₃=0.960
OV 9%	0.72±0.14	0.56±0.08	0.62±0.08	0.70±0.17
P-value		P_1<0.001*	P_2<0.001*	P₃=0.989
OSI P-value	0.41±0.12	0.60±0.19 P_1<0.001*	0.55±0.21 P₂=0.003*	0.43±0.11 P₃=0.992

Table 5 Time courses of the visual quality indicators in the pure ICL implantation and standard ICL implantation groups

	Preoperative		1 day postoperation			1 week postoperation		3 month postoperation
	pure method	standard method		pure method	standard method	pure method	standard method	pure method	standard method
MTF Cut-off frequency	48.48±5.24	47.82±4.18		42.91±6.15	39.79±4.78	45.32±3.60	43.83±4.47	48.88±3.92	47.97±3.93
P-value	P=0.533		P=0.013*			P=0.105		P=0.301
SR	0.25±0.06	0.26±0.05		0.23±0.04	0.21±0.03	0.25±0.06	0.22±0.03	0.26±0.06	0.27±0.05
P-value	P=0.614		P=0.009*			P=0.003*		P=0.707
OV 100%	1.63±0.16	1.62±0.14		1.43±0.20	1.36±0.26	1.52±0.15	1.44±0.28	1.58±0.16	1.60±0.15
P-value	P=0.653		P=0.161			P=0.149		P=0.655
OV 20%	1.26±0.20	1.23±0.26		1.10±0.14	1.01±0.15	1.15±0.23	1.06±0.15	1.27±0.20	1.18±0.26
P-value	P=0.619		P=0.004*			P=0.047*		P=0.116
OV 9%	0.71±0.18	0.72±0.14		0.57±0.12	0.56±0.08	0.70±0.14	0.62±0.08	0.72±0.12	0.70±0.17
P-value	P=0.689		P=0.577			P=0.002*		P=0.630
OSI	0.41±0.11	0.41±0.12		0.60±0.16	0.60±0.19	0.57±0.16	0.55±0.21	0.43±0.11	0.43±0.11
P-value	P=0.850		P=0.932			P=0.762		P=0.954

Notes: P = P-value of the difference between visual quality indicators in the pure ICL implantation and standard ICL implantation groups;

*P < 0.05 = significant difference; MTF = modulation transfer function; OSI = objective scattering index; OV = OQAS value.

Due to technical limitations, table 6,7,8 is only available as a download in the Supplemental Files section.

No competing interests reported.

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Pure ICL Implantation: A Novel Ophthalmic Viscosurgical Device-Free Technique

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