Simple method of measuring ocular rotation in supine position during small incision lenticule extraction

INTRODUCTION

Static cyclotorsion has been a major concern in surgery since the infancy of refractive surgery, and it has been emphasized that rotation of the eyeball during refractive surgery is an important cause of refractive errors left after surgery.Swami

suggested that an average misalignment of 4°could result in 14% of astigmatism not being treated properly,and a 6° difference visible in more than 25% of the eye would result in a 20% undercorrection, and a misalignment of 16° would lead to undercorrection in more than 50% of astigmatism. Previously, static cyclotorsion was measured using various methods, such as using a double Maddox rod

and video-oculography

, and the position change did not have a significant effect on ocular torsion. After the introduction of the eye-tracking system in refractive surgery,research on cyclotorsion has been active. Chernyak

measured the difference in cyclotorsion before and during surgery.The average cyclotorsion of both eyes was approximately 2.0°, and 19 out of 24 patients had binocular excyclotorsion.Subsequent studies generally showed a pattern of binocular excyclotorsion

.

Compared to conventional laser-assisted

keratomileusis,small incision lenticule extraction (SMILE), which has no flap-related complications, provides rapid patient recovery,and has low incidence of dryness, is gaining worldwide popularity and taking over conventional refractive surgery

.However, since its surgical procedure is different from the existing surgery, there is absence of an eye-tracking system in SMILE. Therefore, errors may occur in centering and in the accurate setting of the astigmatism axis during surgery. There are several studies on how to correct these errors; however, all these techniques are manual methods

.

There have been several studies in measuring static cyclotorsion,and among them, Jackson cross cylinder

, Maddox double-rod test

, videokeratography

, and intraoperative measurement were used

. No methods associated to SMILE were reported.In this study, we investigated a method to simply measure the amount of cyclotorsion without the need for extra hardware through anterior slit photography and surgical parameter comparison. In addition, the effect of the amount of cyclotorsion on the surgical results was investigated.

SUBJECTS AND METHODS

Statistical analysis was performed using SPSS software (version 22, SPSS, Inc., USA). Excyclotorsion was indicated by positive values and incyclotorsion by negative values. The mean cyclotorsion indicates the average of these positive or negative values. The absolute value of cyclotorsion indicates the amount of rotation of the eye,regardless of the direction of the cyclotorsion. Chi-square test, Mann-Whitney

test, Wilcoxon signed-rank test,Friedman test, and Pearson’s correlation analysis were used for preoperative and postoperative comparisons. Differences were considered statistically significant at

values less than 0.05.

總之，綜上所述，水肥一體化在我國有著良好的發(fā)展前景，雖然目前在操作中遇到一些問題。但隨著該項技術(shù)的發(fā)展和國內(nèi)環(huán)境的支持，這些問題終將得到解決。本文正是基于對這方面的認(rèn)識，對葡萄種植中水肥一體化推廣和應(yīng)用進行較為詳細(xì)的分析，并以此闡述該項技術(shù)在應(yīng)用中的各種優(yōu)勢。

In this study, we measured intraocular rotation through anterior slit photographs after surgery. The absolute value of the torsional angle was 3.141°±2.256°, and the range of torsion was 0.5°-11.4°. The right eyes tended to be excyclotorted,and the left eyes tended to be incyclotorted. This result is consistent with the results of Park

, Zhao

, and Terauchi

. Zhao

suggested that this result may be due to eye laterality; that is, since the right eye is predominant in many cases, the strength of the oblique muscles of the right eye is stronger and there will be a difference between the two eyes. In correlation analysis, preoperative values such as gender, preoperative corneal thickness, and preoperative intraocular pressure were not correlated with the amount of cyclotosion and the direction of cyclotorsion, and these results are consistent with previous studies.

Anterior slit photographs were taken 1d, 1, 3, and 6mo after surgery. Photographs were taken using a Haag-Street BQ 900 illumination system with the EyeSuite IM 600 imaging module (Haag-Streit International, Koeniz,Switzerland). Photographs were taken by an experienced photographer under indoor lighting. When this picture was taken, the patient kept their eyes straight, the slit beam width was 1 mm, the light source intensity was 60%, and the slit beam angle was 30°. This procedure is represented schematically in Figure 1. Photographs in which the flap was torn during surgery or the incision margins were difficult to distinguish were excluded.

After obtaining the pictures, we calculated the cyclotorsion from the margin of the corneal incision. These calculations were performed using the Image J software (version 1.53i, NIH, USA). First,we checked the upper end of the corneal incision line and drew an imaginary circle along the incision line. A straight line was drawn connecting the upper end of the incision line to the center of the imaginary circle. This straight line was moved counterclockwise to the center of the corneal incision line. The length of incision was 2.5 mm, so it actually moved at a 1.25-mm distance along the contour of the circle. Because the diameter of the circle was 7.5 mm, the counterclockwise shift was calculated to be 19.1°. Theoretically, if there was no cyclotorsion during the surgery, the angle between this straight line and the horizontalline would be 135°. Therefore,by measuring the actual degree of this angle, we could measure the degree of torsion. The method of calculating the cyclotorsion is represented in a schematic diagram in Figure 2.We evaluated the cyclotorsion using photographs taken at 1mo.

To investigate the effect of preoperative parameters on the cyclotorsion, eyes were divided into a group with the amount of cyclotorsion 4 degrees or more and a group with the amount of cyclotorsion less than 4 degrees and analyzed (Table 2).There was no correlation between gender, preoperative corneal thickness, preoperative intraocular pressure, amount of rotation, and direction of rotation. It was found that the smaller the preoperative sphere, the higher the amount of cyclotorsion (

=0.11,

=0.016; Figure 8). There was no significant association between the amount of cyclotorsion and preoperative astigmatism (

=0.758; Figure 9).

To investigate the reproducibility of this measurement method, we measured the cyclotorsion at 1d, 1, 3, and 6mo postoperatively in one patient, and these consecutive data were compared.

本組患者中，累及1個椎體324例，2個椎體96例，3個及以上椎體54例；胸椎384個，腰椎330個。骨密度為（-3.43±0.36）SD。其中OVCF 489個椎體、OVBF 140個椎體、Kummell病85個椎體。具體手術(shù)部位分布詳見表1。

This study was performed in accordance with the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board/Ethics Committee of Chungbuk National University Hospital, Cheongju, Korea.This retrospective study included 484 eyes from 242 patients who underwent SMILE procedures between November 2018 and December 2020 at the Seoul Daabom Eye Center,Cheongju, Korea. The inclusion criteria for this study were corrected distance visual acuity of 20/20 or better, myopia of-1.00 diopters (D) to -9.00 D with astigmatism of 0 to -4.00 D,and stable refraction for more than 1y. The exclusion criteria were the suspicion of keratoconus on corneal topography,severe dry eye, progressive corneal degeneration, the presence of systemic diseases and severe ocular diseases, and a history of intraocular or corneal surgery.

RESULTS

Of the 242 patients, 124 (51.2%)were men and 118 (48.8%) were women, and all patients underwent SMILE surgery in both eyes. The mean age was 28.47±6.44y, and the mean intraocular pressure was 17.55±2.19 mm Hg. The preoperative mean spherical equivalent (SE) was -4.10±1.64 D, the preoperative mean spherical power was -3.70±2.18 D, and the mean astigmatism was -0.82±0.74 D. The mean corneal thickness measured before surgery was 552.64±30.01 μm (Table 1).

UCVA and SE improved significantly after the surgery. The postoperative logarithm of the minimum angle of resolution (logMAR) UCVA was-0.04±0.08 at 1wk, -0.07±0.07 at 1mo, -0.08±0.07 at 3mo, and-0.09±0.07 at 6mo (Figure 3). The mean postoperative SE was 0.03±0.29 at 1wk, 0.01±0.29 at 1mo, -0.04±0.24 at 3mo and-0.03±0.17 at 6mo (Figure 4).

In 484 eyes, 219 (45.2%) eyes had excyclotorsion,235 (48.6%) eyes had incyclotorsion, and 30 (6.2%) eyes had no torsion. In the right eyes, excyclotorsion was 55.0%,incyclotorsion was 38.0%, and no torsion was observed in 7.0% of eyes. In the left eyes, excyclotorsion was 35.5%,incyclotorsion was 59.1%, and there was no torsion in 5.4% of the eyes. Figure 5 is a series of photographs of a representative case. The right eyes tended to be excyclotorted, and the left eyes tended to be incyclotorted and statistically significant(

<0.01, Chi-square test; Figure 6). The mean cyclotorsion was 1.18°±3.69°, and the absolute value of the torsional angle was 3.14°±2.26°. The range of cyclotorsion was 0.5°-11.4°.The distribution of the cyclotorsional angle is shown in Figure 7.In a single patient, the direction and amount of cyclotorsion in the right and left eyes were not correlated with each other(

=0.15,

=0.14, respectively).

Preoperative data such as age, sex,uncorrected distance visual acuity (UCVA), best corrected distance visual acuity (BCVA), manifest refraction, corneal thickness, and intraocular pressure were collected. Patients were examined at 1d, 1, 3, and 6mo postoperatively. When patients visited the clinic, objective and subjective refraction tests were performed, and UCVA and BCVA were recorded.

我國早在2000年就開始實施了國庫管理制度。這一項制度的實施就實現(xiàn)了國庫資金的統(tǒng)一管理，同時，還實現(xiàn)了將財政資金進行直接的劃撥。例如稅收和非稅收的繳費都統(tǒng)一納入財政專戶之中，國庫管理制度的實施，規(guī)范了財政資金的收支，提高了財政資金的管理效率。與此同時，對于預(yù)算的執(zhí)行也建立了動態(tài)的監(jiān)控機制，從而對其進行全面的監(jiān)督，這能夠有效地對預(yù)算的執(zhí)行起到警示的作用。

There was no significant association between the amount of cyclotorsion and postoperative UCVA, refractive outcomes(Table 3). In 98 eyes with astigmatism greater than -1.50 D,correlations between the amount of cyclotorsion, residualastigmatism, and BCVA after surgery were investigated, but there was no statistical correlation.

The ratio of right eye excyclotorsion and left eye incyclotorsion on 1d was higher than that at 1, 3, and 6mo, and this was statistically significant (all

<0.01; Table 4).There was no difference between the 1, 3, and 6mo results in the right and left eyes (

=0.15,

=0.16, respectively).

DISCUSSION

Since SMILE was first announced, it has opened a new horizon of refractive surgery

. It is known that the visual acuity results are comparable to those of conventional surgery, but there have been studies showing that astigmatism and highorder aberration results are inferior

. This result is thought to be influenced by the fact that the contact between the eyeball and the patient interface of the surgical device is required for suction during surgery, which is a deep-seated problemof SMILE, and undesirable decentration may occur during this process. Likewise, due to the absence of an eye-tracking system, errors in the astigmatism axis may occur, which may lead to errors in astigmatism correction

.

In refractive surgery, it is important to precisely cut or ablate the corneal tissue according to the target surgical parameters. Axial misalignment is known to affect the surgery outcomes, and it can induce from the undercorrection of the astigmatism to the formation of a new cylinder axis in severe cases

. Astigmatism axis measurements are performed in an upright position; however, the surgery is performed in a supine position. Therefore, if an eyeball rotation occurs attributed to a change from an upright position to a supine position, axial misalignment can be induced, and the postoperative visual acuity might be affected as a result of axial misalignment.Eyeball rotation through a change in posture is called static cyclotorsion, and numerous studies have been conducted on how it affects the surgical outcome of refractive surgery

.Static cyclotorsion is a major concern in the field of refractive surgery, and various eye-tracking systems have been developed to correct astigmatism axis error

.

All SMILE procedures aimed to obtain emmetropia. All patients received topical anesthesia, standard sterile draping, and speculum insertion. SMILE surgery was performed using a Visumax femtosecond laser (Carl Zeiss Meditec AG, Jena, Germany) with a repetition rate of 500 kHz and pulse energy of 110-140 nJ and followed a previously published surgical procedure. The cap diameter was 7.5 mm,the lenticule diameter was 6.5 mm, and the cap thickness was 120 μm. A single 2.5-mm side cut was made at 135° position.No manual corneal marking or manual compensation of the cyclotorsion was performed. The lenticule was then dissected,separated through the side cut, and manually removed.

數(shù)學(xué)全息定義和非全息定義的教學(xué)目標(biāo)是不同的．按照布魯姆的認(rèn)知水平的層次(“記憶”、“理解”、“運用”、“分析”、“評價”、“創(chuàng)造”)來分類.數(shù)學(xué)定義的教學(xué)目標(biāo)可分為三個層次，即初級目標(biāo)、中級目標(biāo)、高級目標(biāo)．本文將“運用”分為三個層次，即“很簡單的運用”(相當(dāng)于直接運用或直接套公式)、“簡單運用”(包括逆用、變用等)、“靈活運用”．全息定義教學(xué)的初級目標(biāo)是達到“記憶”、“理解”、“很簡單的運用”等層次的要求，中級目標(biāo)是在達到初……