Pupil centroid shift and cyclotorsion in bilateral wavefront-guided laser refractive surgery and the correlation between both eyes

Using a smartphone app in the measurement of posture-related pupil center shift on centration during corneal refractive surgery

Purpose: Pupil center is an important anchor point in corneal refractive surgery, which may affect by body position. This study investigated the feasibility of using a smartphone application in measurement of posture-related pupil center shifts. Methods: Images of undilated eyes were captured for 25 participants (age: 18-38 years) at a distance of 40 cm in four body positions (seated, supine, right lateral, and left lateral) under controlled lighting conditions. During taking images, a smartphone application was used to guide positioning without head rotation and tilt. From the images, the location of the pupil center and pupil diameter with respect to the limbus boundary were measured. Results: According to the data obtained by the smartphone application, pupil center was located slightly nasal and superior to the limbus center in the seated position, and it shifted more nasally and superiorly (p < 0.001, OD 0.54 ± 0.11 mm, OS 0.57 ± 0.14 mm) in the supine position. When body position switched between left and right lateral positions, the pupil centers of both eyes shifted along the direction of gravity (p < 0.05), and no significant shift occurred along the longitudinal axis. Moreover, pupil constriction was observed when the body position changed from seated to supine position (p < 0.001, OD 0.64 ± 0.57 mm, OS 0.63 ± 0.58 mm). Conclusion: Posture-related pupil center shift may be larger than the error tolerance of centration in corneal refractive surgery, which might be difficult to measure by the existing instruments. An accessible application is necessary for evaluating the shift of pupil center and guiding centration during the surgery.

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

AIM

To introduce a novel measurement method of static cyclotorsion in small incision lenticule extraction (SMILE) and to investigate the effect of preoperative parameters on cyclotorsion and the effect of cyclotorsion on postoperative outcomes.

METHODS

The medical records of 242 patients and 484 eyes who underwent SMILE surgery were retrospectively reviewed. Preoperative intraocular pressure, refractive error, and corneal thickness were investigated. Refractive values and visual acuity were measured at 1d, 1, 3, and 6mo. Ocular cyclotorsion in the supine position was measured by calculating the location and angle of the incision site of the cornea in the anterior slit photograph taken after surgery.

RESULTS

Of the total 484 eyes in 242 patients, preoperative mean spherical equivalent (SE) was -4.10±1.64 D, and the mean astigmatism was -0.82±0.74 D. Uncorrected distance visual acuity (UCVA) and SE improved significantly after the surgery. Moreover, 219 (45.2%) eyes had excyclotorsion, 235 (48.6%) eyes had incyclotorsion, and 30 (6.2%) eyes had no torsion. The right eyes tended to be excyclotorted, and the left eyes tended to be incyclotorted (P<0.01). The mean cyclotorsion was 1.18°±3.69°, and the mean absolute value of cyclotorsion was 3.14°±2.26°. The range of cyclotorsion was 0.5°-11.4°. It was found that the smaller the preoperative sphere, the higher the amount of cyclotorsion (r=0.11, P=0.016). There was no significant association between the amount of cyclotorsion and preoperative astigmatism. There was no correlation between sex, preoperative corneal thickness, preoperative intraocular pressure, amount of cyclotorsion, and direction of cyclotorsion. The ratio of right eye excyclotorsion and left eye incyclotorsion on 1d was higher than that at 1, 3, and 6mo (all P<0.01). There was no difference between the 1, 3, and 6mo results in the right and left eyes (P=0.15, P=0.16, respectively).

CONCLUSION

The newly devised ocular cyclotorsion measurement method can be used to evaluate ocular cyclotorsion after SMILE. Preoperative SE is associated with the amount of cyclotorsion, however, cyclotorsion doesn't have a significant effect on the results of SMILE surgery.

Clinical outcomes of corneal refractive surgery comparing centration on the corneal vertex with the pupil center: a meta-analysis

PURPOSE

To compare the visual and refractive outcomes between centration on the corneal vertex and the pupil center in corneal refractive surgery.

METHODS

A comprehensive literature search was conducted using PubMed, MEDLINE, EMBASE, and the Cochrane Library to identify relevant studies. The primary outcomes were the postoperative spherical equivalent (SE), effectiveness [uncorrected distance visual acuity (UDVA) ≥ 20/20, eyes within ± 0.50 diopter (D) of target refraction], and safety [loss ≥ 2 lines of corrected distance visual acuity (CDVA)]. Higher-order aberrations were considered secondary outcomes.

RESULTS

Seven studies describing a total of 1964 eyes were included in this meta-analysis. A statistical significance in postoperative SE was found between the two centration methods for the correction of myopia that favor the CV-centered method (p < 0.001). No significant differences were observed in the proportion of eyes with UDVA ≥ 20/20 or loss ≥ 2 lines of CDVA postoperatively. However, the proportion of eyes within ± 0.50 D was slightly higher (p = 0.02) and the coma aberration was much lower in the corneal vertex-centered method (p < 0.001).

CONCLUSION

Preferable visual and refractive outcomes could be achieved with either centering on the corneal vertex or pupil center in corneal refractive surgery; however, the corneal vertex-centered method has shown partial benefits in some clinical indices. In order to obtain higher quality of clinical evidences, more randomized controlled trials (RCTs) are required in further investigations.

Lower- and higher-order aberrations after photorefractive keratectomy with and without compensation of pupil centroid shift: fellow eye comparison

PURPOSE

To study the effect of pupil centroid shift (PCS) compensation on lower- and higher-order aberrations (HOAs) after photorefractive keratectomy (PRK).

SETTING

Labbafinejad Medical Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.

DESIGN

Prospective intrasubject fellow eye study.

METHODS

One hundred twelve eyes of 56 patients with simple myopia or myopic astigmatism scheduled for PRK were enrolled. Preoperatively, the amount of PCS was measured in the horizontal and vertical directions. All eyes received wavefront-optimized treatment with static cyclotorsion compensation. PCS compensation was turned on for the right eye of each subject (PCS-on group), and turned off for the left eye (PCS-off group). Postoperatively, refraction and corneal HOAs were compared between the study groups at 6 months.

RESULTS

Mean preoperative myopia was -3.84 diopters (D) ± 2.41 (SD) vs -3.75 ± 2.27 D (P = .408), whereas mean preoperative cylinder was -1.18 D ± 1.15 (SD) vs -1.14 ± 1.16 D (P = .769) in the PCS-on and PCS-off groups, respectively. Mean absolute PCS values were 62.25 μm ± 41.82 (SD) vs 55.92 ± 37.47 μm (P = .45) in the horizontal direction and 65.04 ± 47.16 μm vs 58.40 ± 45.44 μm in the vertical direction (P = .29) in the PCS-on and PCS-off groups, respectively. The study groups were comparable in terms of postoperative refraction and root mean square of total corneal HOAs.

CONCLUSIONS

Compensation of PCS did not affect lower- and higher-order aberrations after wavefront-optimized PRK with static cyclotorsion compensation in myopic or myopic astigmatic eyes.

Posture-related ocular cyclotorsion during cataract surgery with an ocular registration system

Ocular cyclotorsion when a patient changes from seated to supine position in cataract surgery and factors predicting the amount of cyclotorsion were investigated using VERION system. Variables analyzed were age, gender, preoperative visual acuity, axial length, laterality of eyes, operative duration, and the direction and degree of cyclotorsion. The mean cyclotorsion of 107 eyes of 93 cataract patients was 0.98 ± 4.85 degrees (median, 1 degree; range, -11 to 12 degrees), and the median absolute value was 4 degrees (mean, 4.05 ± 2.82 degrees; range, 0 to 12 degrees). Cyclotorsion was ≥3 degrees in 68 (63.6%) eyes. Excyclotorsion occurred more frequently than incyclotorsion (50.5% vs. 43.0%). There was no cyclotorsion in seven (6.5%). Multiple regression analysis showed that gender was a significant predictive factor for the absolute value of cyclotorsion (β = 1.06, P = 0.041); however, the other variables had no effect on cyclotorsion. The absolute value of cyclotorsion was significantly larger in female than in male patients [median, 4 degrees and 3 degrees, respectively; mean, 4.66 ± 3.02 degrees and 3.44 ± 2.52 degrees, respectively (P = 0.039)]. In conclusion, cataract patients had significant posture-related ocular cyclotorsion. The amount of cyclotorsion was larger for female than male patients.

Reliability and reproducibility of disc-foveal angle measurements by non-mydriatic fundus photography

Purpose

Abnormal torsion could be associated with cyclovertical strabismus, but torsion measurements are not reliable in children. To assess an objective fundus torsion evaluation in a paediatric population, we used Non-Mydriatic Fundus photography (NMFP) in healthy and cyclovertical strabismus patients to evaluate the disc-foveal angle over time and observers.

Methods

We used a retrospective set of NMFP including 24 A or V-pattern strabismus and 27 age-matched normal children (mean age 6.4 and 6.7 years respectively), taken during 2 distinct follow-up consultations (separated by 251 and 479 days respectively). Each disc-foveal angle measurement (from which the ocular torsion can be assessed) was performed by 5 different observers, using graphical software and based on reproducible fundus anatomical marks. Statistical analysis was performed with a multivariate ANOVA using group, time and observers as factors, in addition to intraclass coefficient correlation (ICC) to assess measurement reproducibility.

Results

A significant difference of disc-foveal angle measures was observed between groups (p<0,001): 18.73° (SD = 6.42), -3,25° (SD = 5.51) and 6,89° (SD = 4,41) respectively for V-pattern, A- pattern and normal subjects. Neither observers (F = 0,2028 p = 0,9369) nor time between 1^st and 2^nd NMFP (F = 0,6312 p = 0,4271) seem to influence the measure of disc-foveal angle. The evaluation of disc-foveal angle was very reproducible between observers (ICC>0,97).

Conclusion

Abnormal amount of objective torsion could be associated with alphabet-pattern strabismus. Disc-foveal angle evaluation by NMFP in a children population appears as a non-invasive, reliable and reproducible method.

Shifting of the Line of Sight in Tilted Disk Syndrome

OBJECTIVES

To investigate the shifting of the line of sight (LoS) and the refractive, topographic, and aberrometric parameters that may be associated with the shifting of the LoS in eyes with tilted disk syndrome (TDS).

METHODS

Eighty left eyes of 80 subjects with TDS (Study Group) and 70 left eyes of 70 subjects with myopia and astigmatism (Control Group) were included in this study. Line-of-sight coordinates on the horizontal (x) and vertical (y) axes, refractive, topographic, and aberrometric parameters were evaluated. All parameters were compared between groups, and correlations were analyzed for the study group.

RESULTS

In the study group, the LoS significantly shifted to the superotemporal direction compared with the control group (P=0.022 and P=0.008 respectively). The shift on y-axis was correlated with mean cylindrical refractive error (r=-0.283, P=0.011), total root mean square (RMS) (r=0.321, P=0.004), higher-order aberration RMS (r=0.300, P=0.007), vertical coma (r=0.430, P<0.001), and vertical trefoil values (r=-0.455, P<0.001).

CONCLUSIONS

Results demonstrated a superotemporal shifting of the LoS in eyes with TDS. As eyes with TDS have an important place among candidates for refractive and multifocal intraocular lens implantation surgeries, this shift must be accounted for to prevent decentralization and provide satisfactory outcomes.

Assessment of bilateral pupillary centroid characteristics at varying illuminations and post-photopic flash response using an automated pupillometer

BACKGROUND

The aim was to assess the symmetry and magnitude of illumination-dependent centroid shift and of post-photic flash re-dilatation response for normal pupils.

METHODS

This cross-sectional, observational, inter-eye comparative study was performed at a specialty hospital. Fifty eyes (25 volunteers) without any ocular abnormality underwent pupillometry for scotopic (0.4 lux), mesopic (4.0 lux), photopic conditions (40 lux) and for rate of pupillary re-dilatation after a photopic flash (500 lux) with an inbuilt pupillometer on a Scheimpflug device (Sirius, CSO, Italy). Main outcome measures were pupillary centroids at different illuminations and time-dependent pupil diameters after a photic flash response.

RESULTS

The mean pupil size for scotopic, photopic and mesopic pupils were significantly different (p < 0.001, ANOVA) for right and left eyes, analysed separately. The post-photic flash re-dilatation diameter was measured at zero, one, two, four, six, eight and 10 seconds after the flash. The mean diameters at given times post-photic flash were comparable in fellow eyes (p > 0.5, t-test) and highly correlated (r ≥ 0.8, p < 0.05 at all timed comparisons). The mean pupil diameter followed a time-dependent cubic function for both the right and left eyes. Speed was also governed by a time-dependent cubic function for both the right and the left eyes.

CONCLUSIONS

Fellow eye symmetry is seen in illumination-governed centroid shifts and the post-flash re-dilatation response. The pupil dilates back briskly with a time-dependent cubic function, which is similar for fellow eyes in normal patients.

Optical eye tracking system for real-time noninvasive tumor localization in external beam radiotherapy

PURPOSE

External beam radiotherapy currently represents an important therapeutic strategy for the treatment of intraocular tumors. Accurate target localization and efficient compensation of involuntary eye movements are crucial to avoid deviations in dose distribution with respect to the treatment plan. This paper describes an eye tracking system (ETS) based on noninvasive infrared video imaging. The system was designed for capturing the tridimensional (3D) ocular motion and provides an on-line estimation of intraocular lesions position based on a priori knowledge coming from volumetric imaging.

METHODS

Eye tracking is performed by localizing cornea and pupil centers on stereo images captured by two calibrated video cameras, exploiting eye reflections produced by infrared illumination. Additionally, torsional eye movements are detected by template matching in the iris region of eye images. This information allows estimating the 3D position and orientation of the eye by means of an eye local reference system. By combining ETS measurements with volumetric imaging for treatment planning [computed tomography (CT) and magnetic resonance (MR)], one is able to map the position of the lesion to be treated in local eye coordinates, thus enabling real-time tumor referencing during treatment setup and irradiation. Experimental tests on an eye phantom and seven healthy subjects were performed to assess ETS tracking accuracy.

RESULTS

Measurements on phantom showed an overall median accuracy within 0.16 mm and 0.40° for translations and rotations, respectively. Torsional movements were affected by 0.28° median uncertainty. On healthy subjects, the gaze direction error ranged between 0.19° and 0.82° at a median working distance of 29 cm. The median processing time of the eye tracking algorithm was 18.60 ms, thus allowing eye monitoring up to 50 Hz.

CONCLUSIONS

A noninvasive ETS prototype was designed to perform real-time target localization and eye movement monitoring during ocular radiotherapy treatments. The device aims at improving state-of-the-art invasive procedures based on surgical implantation of radiopaque clips and repeated acquisition of X-ray images, with expected positive effects on treatment quality and patient outcome.

Vector analysis of low to moderate astigmatism with small incision lenticule extraction (SMILE): results of a 1-year follow-up

BACKGROUND

To evaluate the refractive outcomes for the correction of low to moderate astigmatism up to 1 year following small incision lenticule extraction (SMILE) surgery.

METHODS

This retrospective study enrolled 98 eyes from 98 patients who underwent SMILE surgery for the correction of myopia and astigmatism. Only right eyes were included in this study to avoid the bias of orientation errors. The vector method was used to analyze the outcomes of astigmatism at 1 month, 6 months and 12 months after the procedure, including the double-angle plots, correction index (CI), index of success (IOS), angle of error (AofE) and magnitude of error (MofE). The effectiveness, safety, stability and predictability were also investigated during the 12-month follow-up.

RESULTS

The preoperative cylinder ranged from -2.75 D to -0.25 D (average of -0.90±0.68 D), and the mean postoperative cylinder values were -0.24±0.29 D, -0.24±0.29 D, and -0.20±0.27 D at 1 month, 6 months, and 12 months, respectively. The mean astigmatism in vector form was -0.14 D×27.19° at 1 month, -0.13 D×27.29° at 6 months, and -0.10 D×28.63° at 12 months after surgery. The CI was 1.00±0.32 and IOS was 0.29±0.44 at the 12-month follow-up. Significant negative correlations were found between the CI and absolute target induced astigmatism (TIA) value, and positive correlations were found between the IOS and absolute AofE value (P<0.05). The MofE was limited within ±1.00 D at the 12-month follow-up. Fifty-six eyes (57.1%) gained one line in corrected distance visual acuity (CDVA) and five eyes (5.1%) gained two lines. There were no significant differences observed in the refractive outcomes among time points.

CONCLUSIONS

SMILE surgery was effective and safe in correcting low to moderate astigmatism, and stable refractive outcomes were observed at the long-term follow-up. The undercorrection of astigmatism could possibly be influenced by attempted astigmatism correction preoperatively, the axis rotation during the surgery or wound healing postoperatively. This study suggested that nomograms should be adjusted in correcting astigmatism with SMILE surgery.

Clinical utility and assessment of cyclodeviation

PURPOSE OF REVIEW

This article reviews and updates basic concepts, diagnosis and treatment of cyclotorsion.

RECENT FINDINGS

Cyclodeviation in congenital superior oblique palsy (SOP) seems to correlate with the extent of superior oblique muscle hypoplasia. Genetic polymorphisms such as PHOX2B polymorphism, considered to be risk factors for congenital fibrosis of the extraocular muscles, may play a role in SOP and consequently in cyclotorsion. Two components of the ocular tilt reaction, ocular torsion and tilt of subjective visual vertical, seem to share similar sites of impairment in the brainstem. Harada-Ito surgery continues to be the procedure of choice in patients with isolated cyclodeviation, evidencing better outcome if less than 10° of preoperative excyclotorsion and preoperative fusion exist. Ocular torsion is not infrequent in patients with intermittent exotropia, especially in the most exo-deviated eye, emphasizing a possible role in pathogenesis. A new device for the assessment of dynamic torsion during ocular counter roll response using after-image has been described. Similarly, a new method to measure objective ocular torsion using retinal arcade tilt as a reference has been proposed. Finally, torsional data transformation such as the sum of angles of excyclodeviation, rather than using the angle of excyclodeviation of the paretic eye, is becoming increasingly popular among studies on torsion.

SUMMARY

Exciting developments on ocular torsion have been described recently, and new ways to access and interpret ocular torsion have been devised as well.