Performance of Patients With Deficient Stereoacuity on the EYESi Microsurgical Simulator




Purpose


To compare the performance of individuals with deficient stereoacuity with that of individuals with normal stereoacuity on a microsurgical task using the VRMagic EYESi Ophthalmosurgical Simulator (VRmagic Holding AG).


Design


Prospective, experimental study at a single institution.


Methods


Subjects with abnormal stereoacuity and controls with normal stereoacuity completed a total of 4 attempts on 2 standardized microsurgical tasks on the EYESi Simulator. Performance was quantified using a 60-point scale, and scores were compared using the Wilcoxon rank-sum test with a significance level of .05 assumed for all tests.


Results


Twenty-one subjects with deficient or absent stereoacuity and 21 control subjects with normal stereoacuity were included. The mean age of both groups was 31.5 years (range, 10 to 64 years). Twenty-nine (69%) participants were male. The 2 groups did not differ in age or gender. For each of the 4 module attempts, the Wilcoxon rank-sum test showed significantly better performance of individuals in the control group compared with the study group ( P < .001). Additional attempts did not result in improved performance by the study group compared with the control group. No significant associations were observed between performance scores and age or gender.


Conclusions


This study compared the performance of patients with deficient stereoacuity with that of those with normal stereoacuity in microsurgical tasks. Individuals with normal stereoacuity performed better than those with deficient stereoacuity in a simulated microsurgical task. A larger and more complex study may be necessary to validate the findings of the present investigations.


Depth perception is the visual ability to perceive the world in 3 dimensions. It relies on cues from both monocular and binocular stimulation of the retina and visual cortex. Stereopsis is a particularly refined form of binocular fusion resulting from neural processing of the relative horizontal binocular disparities between monocular retinal projections. Stereopsis can be lost as a result of a deficit in binocular vision. Examples include individuals who have lost the use of one eye secondary to trauma or disease, as well as those individuals with monofixation syndrome, a form of sensory adaptation secondary to subnormal binocular vision. Monofixation syndrome can be the result of small-angle strabismus, anisometropia, or occlusion amblyopia, or it may occur as a primary defect in central binocular vision. Patients with monofixation syndrome have a unilateral central suppression scotoma and maintain peripheral fusion under binocular viewing conditions, with a resultant deficit in stereopsis. The prevalence of monofixation syndrome in the general population in the United States is approximately 1%.


The VRMagic EYESi Ophthalmosurgical Simulator (VRmagic Holding AG, Mannheim, Germany) is a device that was designed for intraocular microsurgical training ( Figure 1 ). The premise for its development was based on flight simulators used to train pilots for civil aviation. During simulated surgery, the participant manipulates handheld instruments that are inserted into an artificial eye. The motion and orientation of the instruments are interpreted by sensors and are transmitted to a computer, which then renders the virtual operation scenario into the EYESi microscope. Although the simulator software adapts to individual actions of each participant, each module is highly reproducible, providing identical tasks and objective measures of performance.




FIGURE 1


Photograph showing the VRMagic EYESi Ophthalmosurgical Simulator (VRmagic Holding AG, Mannheim, Germany). During simulated microsurgery with this device, the participant views an image through a microscope and manipulates handheld instruments that are inserted into an artificial eye.


It is unclear if individuals with deficient stereopsis perform similar to, or worse than, individuals with normal stereopsis on manual tasks that theoretically necessitate refined binocular function. Assuming that certain, if not all, modules require good depth perception and stereoacuity to perform a given surgical task, we hypothesized that individuals with normal stereopsis would perform better than those with either deficient or absent stereoacuity. We set out to test this hypothesis using the VRMagic EYESi Ophthalmosurgical Simulator.


Methods


A prospective experimental study was conducted at the Cole Eye Institute in Cleveland, Ohio. Inclusion criteria for the study group included deficient stereoacuity (80 seconds of arc or less on the Titmus stereotest; Stereo Optical Company, Chicago, Illinois, USA) and binocular best-corrected Snellen visual acuity of 20/40 or better. Inclusion criteria for the control group included normal stereoacuity (60 seconds of arc or more on the Titmus stereotest), best-corrected Snellen visual acuity of 20/40 or better in each eye, and otherwise normal eye examinations. Additional inclusion criteria for both groups included the ability to sit at the simulator device and age between 10 and 75 years. Exclusion criteria for both groups included ongoing therapy for amblyopia, recent intraocular or periocular surgery (within the preceding 60 days), prior microsurgical experience, and the presence of mental deficiency or other physical or mental reason for impaired performance.


Subjects completed two standardized, highly reproducible anterior segment modules on the VRMagic EYESi Ophthalmosurgical Simulator. During these tasks, subjects manipulated a handheld probe (controlled by the subject’s dominant hand) with its tip inserted into the anterior segment of the artificial eye. The goals of the assigned tasks were: (1) to touch the probe tip to several target spheres dispersed at various depths in the anterior chamber, (2) to maintain efficient control of the eye and probe, and (3) to avoid touching the probe tip to the iris, lens, and cornea ( Figure 2 ). Subjects performed 3 consecutive attempts on the first difficulty level module, followed by 1 attempt on the third difficulty level module. This final module was graded as a higher difficulty level because of variation in target size and depth of location within the anterior chamber. Subjects were given up to 4 minutes to attempt the completion of each module.




FIGURE 2


Microscope views of the anterior segment module on the VRMagic EYESi Ophthalmosurgical Simulator (VRmagic Holding AG, Mannheim, Germany) used in this study. The participant uses a handheld probe to touch sphere targets lying at variable depths in the anterior chamber of the simulated eye. The second image depicts damage to the lens and anterior capsule, whereas the third image depicts damage to the corneal endothelium.


Each subject’s performance was quantified using a predetermined scale totaling 60 points. Scores were based on the subject’s ability to touch each target site in the allotted time; ability to avoid the lens, iris, and cornea; speed and efficiency of movements; ability to maintain zonular stability; and ability to maintain the probe tip and target sites in focus.


Scores were compared between the study and control groups using the Wilcoxon rank-sum test. Scores were compared additionally between age groups and genders using Wilcoxon rank-sum tests, Pearson chi-square tests, and Spearman correlations. For the first module, which was repeated for a total of 3 attempts, the interval improvement of the performance scores between consecutive attempts was compared, also using Wilcoxon rank-sum tests, to evaluate each group’s ability to improve performance with practice. All statistical analyses were conducted using SAS software version 9.2 (SAS Institute, Cary, North Carolina, USA). A significance level of .05 was assumed for all comparisons.




Results


A total of 42 patients were recruited into the study: 21 patients with deficient or absent stereoacuity and 21 control patients with normal stereoacuity. Results are given in Table 1 . The mean age of the 42 subjects was 31.5 years (range, 10 to 64 years). The median and mean ages were 30 and 32 years, respectively, in the study group, and 29 and 31 years, respectively, in the control group. Of the 42 subjects, 29 (69%) were male, 15 within the study group and 14 within the control group. Based on these demographics, there was no difference between the study and control groups in age and gender ( P = .92, Wilcoxon rank-sum tests for age; P = .74, Pearson chi-square tests for gender).



TABLE 1

Results of Data Set: Characteristics of Study Group and Control Group, Including Age, Sex, Binocular Vision, Level of Stereoacuity, and Cause of Deficient Stereoacuity If Present























































































































































































































































































































































































































































































































Patient No. Age (yrs) Sex Binocular BCVA Stereoacuity a (Seconds of Arc) Cause of Deficient Stereoacuity, If Present EYESi Simulator Scores
Level 1 Level 3
First Attempt Second Attempt Third Attempt
Study group
1 10 M 20/20 200 Accommodative Esotropia 0 0 0 0
2 12 F 20/30 3000 Esotropia 0 0 0 0
3 49 F 20/20 absent Duane syndrome with esotropia 0 0 0 0
4 64 M 20/20 100 Exotropia 0 33 33 0
5 15 M 20/15 400 Congenital SO palsy with hypertropia 0 0 0 0
6 37 F 20/30 absent Anisometropic amblyopia 0 24 2 0
7 17 M 20/20 absent Exotropia with DVD 0 0 0 0
8 55 M 20/25 3000 Exotropia 0 0 6 0
9 30 M 20/15 absent Esotropia 0 0 0 0
10 12 M 20/20 absent Anisometropic amblyopia 0 37 31 0
11 15 M 20/25 absent Esotropia 0 0 8 0
12 21 M 20/40 3000 Nystagmus 9 34 34 0
13 14 F 20/20 absent Esotropia 31 11 8 0
14 39 M 20/20 200 Anisometropic amblyopia 12 33 36 0
15 40 M 20/20 absent Exotropia 27 0 28 0
16 14 M 20/20 absent NLP vision in 1 eye secondary to total RD 29 39 46 0
17 30 M 20/20 absent Exotropia 0 0 0 0
18 59 M 20/20 absent Anisometropic amblyopia 0 0 0 0
19 61 F 20/20 absent Anisometropic amblyopia 0 17 38 0
20 57 F 20/30 absent Anisometropic amblyopia 31 36 35 8
21 20 M 20/25 3000 Esotropia 0 0 4 2
Control group
22 29 M 20/20 40 33 32 33 8
23 32 M 20/20 60 58 57 55 28
24 10 M 20/20 40 16 23 22 0
25 14 M 20/20 40 0 0 0 19
26 12 M 20/20 40 0 0 0 0
27 55 F 20/20 40 29 23 35 8
28 28 M 20/30 40 57 60 60 57
29 20 M 20/20 40 36 33 47 52
30 22 F 20/15 40 56 54 32 8
31 30 F 20/20 40 32 59 55 35
32 30 F 20/20 40 39 39 59 31
33 62 M 20/20 40 0 0 0 0
34 30 M 20/25 40 31 36 37 0
35 21 F 20/20 60 19 58 53 47
36 31 F 20/20 40 35 59 53 54
37 29 M 20/25 40 58 59 60 59
38 23 F 20/20 60 33 34 38 32
39 27 M 20/20 40 35 49 59 39
40 45 M 20/20 50 51 39 59 57
41 56 M 20/20 40 37 60 59 32
42 47 M 20/20 40 36 49 51 0

BCVA = best-corrected Snellen visual acuity; DVD = dissociated vertical deviation; F = female; M = male; NLP = no light perception; SO = superior oblique; RD = retinal detachment; yrs = years.

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Jan 16, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Performance of Patients With Deficient Stereoacuity on the EYESi Microsurgical Simulator

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