Accuracy of segmented measurement of axial length in ultra-high myopia filled with silicone oil using immersion B-scan ultrasonography

INTRODUCTION

With the development of vitrectomy and the accurate mastery of the operative indications of silicone oil filling, a considerable number of patients with complex retinal detachment and vitreoretinal proliferative diseases can preserve good retinal function after vitrectomy combined with silicone oil filling

. Cataract is the most important complication after silicone oil filling

. At present, the surgery method combined silicone oil extraction with cataract extraction and intraocular lens implantation is widely used to treat this complication in China and other countries

. The accurate measurement of axial length (AL) is related to the intraocular lens (IOL)implantation and determines the postoperative visual function for patients with this kind of cataract. As a novel optical coherent biometric device, IOLMaster is easily-manipulated,non-contact, accurate and non-invasive

. However, due to the dependency of IOLMaster on optical principle, the ALs of patients with severe cataract cannot be accurately measured,and the traditional A-ultrasound measurement is still needed.Clinically, the ALs of most patients can be accurately measured by the traditional A-ultrasound. However, for patients with high myopia, especially those with ultra-high myopia before surgery, the pseudo prolongation of vitreous cavity caused by long vitreous cavity and silicone oil filling, intermingled with severe opacity of lens on ultrasonic propagation, retinal waves are often difficult or impossible to be measured in A-ultrasound. This leads to pseudo short AL or eye axis or large deviation and poor repeatability of AL.

To address the abovementioned clinical issues, based on our previous findings of immersion A/B ultrasound in accurately measuring the AL of high myopia

, we evaluated the accuracy of immersion B-scan segmented measurement of ALs in ultra-high myopia patients with cataract secondary to silicone oil filling by comparing with IOLMaster 500,providing a theoretical basis for its clinical application.

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SUBJECTS AND METHODS

Clinically, for patients with cataract after vitrectomy combined with silicone oil filling due to retinal detachment,the ultimate goal of silicone oil extraction combined withcataract extraction and IOL implantation is to preserve the residual visual function as much as possible. The factors affecting visual function include patient- and surgery-related factors

. In this study, no significant intergroup differences in age, gender, and ALs were found, and all the causes of retinal detachment were relatively uniform. The difference in preoperative uncorrected visual acuity between the two groups was mainly due to the various severity of lens opacity, and the opaque lens would be removed, so the influence of this factor on our results could be excluded. Surgery-related factors include surgical proficiency, surgical incision, IOL selection,and IOL implantation accuracy

.

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From June 2016 to June 2020, a total of 67 ultrahigh myopia inpatients (67 eyes) who underwent silicone oil removal combined with cataract extraction and IOL implantation were retrospectively enrolled. The preoperative AL of 31 patients with severe cataract were segmented measured using immersion B-scan (B-scan group) and another 36 patients with mild or moderate cataract were measured using IOLMaster 500 (IOLMaster group). All patients of both groups were injected with 5500

silicone oil (Baush&Lomb Oxane, USA) during vitrectomy. Inclusive criteria: 1) ultrahigh myopia (refractive diopter＜-10.00 D or AL＞28 mm); 2)all the eyes to be operated had a certain gazing ability (they could continuously gaze at IOLMaster or be fixed in the first eye position for more than 3s in the imaging process of immersion B-scan); 3) without other serious ocular diseases,other systemic or ocular diseases that affect the examination or surgery; 4) scheduled silicone oil removal when complete retinal reattachment was achieved within 6mo after silicone oil injection. Exclusion criteria were as follows: 1) silicone oil emulsification within 6mo after primary silicone oil injection;2) silicone oil removal for various postoperative complications within 6mo after silicone oil injection; 3) other ophthalmic surgeries during the period between primary silicone oil injection and removal; 4) with uncomplete follow-up data.

Before the surgery, the anterior parts (cornea, anterior chamber, iris and lens) and anterior vitreous body of all patients were examined using slit lamp, the intraocular pressure (IOP) was measured by using non-contact tonometer and the fundus was examined by A/B ultrasonic diagnosis apparatus.

Statistical Analysis Statistical analyses were performed using SPSS12.0 software. Chi-square test was used to compare the gender difference of both groups. The difference of ALs before and after surgery of both groups, and postoperative absolute refractive error and BCVA between both groups were compared using

-test. The rank sum test was used to compare the distribution of absolute refractive error between the two groups in the range ±0.50, ±1.00, and ±1.50 D. The statistical level was set to

=0.05.

鈣硫比的增加對所獲得的粉煤灰脫硫活性起到促進作用，但CaCO3的增加必然對爐內煤粉燃燒特性產生影響，若其加入嚴重影響煤粉燃燒特性，那么對上述研究就失去了意義。為此，筆者進一步針對鈣硫比對煤粉燃燒特性的影響進行研究。

After retrobulbar anesthesia, the surgery was performed with Alcon Legacy 20000 phacoemulsification apparatus. A 3 mm incision (I-shape) parallel to the lamellar sclera was made (11 o’clock, 2 mm behind limbus). A 3.2 mm triangular knife was used and viscoelastic agent (AVI)was injected into anterior chamber. Continuous circular capsulorhexis was performed with a diameter of 5.5-6 mm. A corneal auxiliary incision was made at 9 o’clock (left eye) or 3 o’clock (right eye). Lens cortex was aspirated by auto-I/A system. The silicone oil was extracted with cannula needle and syringe under negative pressure with an incision at the upper pars plana. After the silicone oil was completely removed,the retina was observed by pan-retinoscopy. Then, a single focus foldable IOL (Rayner 620H, UK) was implanted into the capsule.

A total of 31 (31 eyes) with severe cataract were enrolled as the B-scan group, including 21 males and 10 females, aged from 25 to 59y (mean 42.8±9.8y). The preoperative visual acuity was light perception (LP) or hand move (HM)

before eye. And 36 patients (36 eyes) were enrolled as IOLMater group, including 23 males and 13 females, aged from 24 to 61y(mean: 41.9±9.5y). The preoperative visual acuity was finger counting (FC) to 0.25, as shown in Table 1.

This formula was utilized to calculate the required IOL power in our present study. In view of the comparative uniformity of patient, surgeon, surgery method, IOL type and calculation formula, we deemed that the biometric measurements were the main reason influencing the differences between the methods in this study. Studies have proposed that 54% deviation between actual diopter and prediction of diopter after cataract surgery comes from AL measurement, whereas 38% predicted from postoperative ACD and another 8% came from the evaluation of corneal curvature. Therefore, the accuracy of preoperative eye AL measurement is of particular importance

. In this study, the corneal curvature and ACD were measured using IOLMaster. AL is an indicator avoid refractive errors.Therefore, the main goal of this study is to investigate how to minimize the ALs measurement error.

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