OBJECTIVES: There has been continuous development in the area of stereoscopic medical imaging devices, and many stereoscopic imaging devices have been realized and applied in the medical field. In this article, we review past and current trends pertaining to the application stereo-imaging technologies in the medical field. METHODS: We describe the basic principles of stereo vision and visual issues related to it, including visual discomfort, binocular disparities, vergence-accommodation mismatch, and visual fatigue. We also present a brief history of medical applications of stereo-imaging techniques, examples of recently developed stereoscopic medical devices, and patent application trends as they pertain to stereo-imaging medical devices. RESULTS: Three-dimensional (3D) stereo-imaging technology can provide more realistic depth perception to the viewer than conventional two-dimensional imaging technology. Therefore, it allows for a more accurate understanding and analysis of the morphology of an object. Based on these advantages, the significance of stereoscopic imaging in the medical field increases in accordance with the increase in the number of laparoscopic surgeries, and stereo-imaging technology plays a key role in the diagnoses of the detailed morphologies of small biological specimens. CONCLUSIONS: The application of 3D stereo-imaging technology to the medical field will help improve surgical accuracy, reduce operation times, and enhance patient safety. Therefore, it is important to develop more enhanced stereoscopic medical devices.
Asthenopia ; Depth Perception ; Diagnostic Imaging ; Laparoscopy ; Patient Safety ; Vision Disparity ; Vision, Ocular

Visual conditions such as anisometropia, monovision and monocular undercorrection affect the combination of visual input from both eyes. This study investigated the effects of monocular blur, in binocularly normal participants, on stereoacuity and binocular contrast sensitivity. Fifteen young adults (age range between 19 and 23 years old) with normal visual acuity and binocular vision participated in this study. Stereopsis was measured using the TNO test with a series of positive spherical lenses placed before the dominant eye. The procedure was repeated using the Titmus Stereotest on five participants as a control experiment. Monocular and binocular contrast sensitivities were also measured using the Pelli-Robson Contrast Sensitivity Chart. Blur was induced monocularly with a series of positive spherical lenses placed before the dominant eye and binocular contrast sensitivity was re-measured. Stereopsis scores decreased significantly when monocular blur was imposed. Across blur levels, absolute stereopsis scores measured with TNO test were worse than those measured with Titmus stereotest (all p < 0.05). However, the ratio of scores obtained without blur and under monocular blur appeared to be similar for both tests. Stereopsis without blur was between 6.82× to 8× better than that obtained with the highest level of imposed monocular blur. Binocular contrast sensitivity score decreased significantly with increasing level of monocular blur (p < 0.01). Binocular contrast sensitivity score without blur was 1.62× better than that obtained under binocular viewing with highest level of imposed blur. Stereopsis tests are more sensitive than measurements of binocular contrast sensitivity as an indicator of interocular acuity discrepancies which could occur in anisometropic or monovision patients. However, the choice of stereopsis test is crucial, as the TNO test appears to be more sensitive to monocular blur than the Titmus stereostest.
Depth Perception

PURPOSE: To study the effect of spherical lens induced aniseikonia on stereopsis and fusion. METHODS: One hundred subjects, with normal binocular function without any ophthalmic disease or surgery history, were examined. The aniseikonia was induced with spherical lenses in 1 diopter (D) stepwise manner from -2 D to +2 D. The amount of aniseikonia was measured by Awaya's New Aniseikonia Test. Stereopsis and fusion were determined with Titmus Stereo Test and fusion card of major amblyoscope respectively. RESULTS: As the amount of aniseikonia was increased, the stereopsis and fusion were decreased. The change was statistically significant (ANOVA, p<0.001). Aniseikonia was more correlated to fusion than stereopsis. A significant decline in the stereopsis was detected when the size of aniseikonia changed from 1% to 2%. A significant decline in fusion was noticed when aniseikonia changed from 2% to 3% (Independent t-test, p<0.01). CONCLUSIONS: Our study suggests that binocular function can be disturbed by experimentally induced aniseikonia in normal subjects and that stereoacuities and fusional amplitude can be decreased as the degree of aniseikonia becomes larger.
Aniseikonia* ; Depth Perception ; Telescopes*

The commonly used tests for stereopsis are Titmus-fly, Randot, and TNO tests. In this study, 50 normal subjects were tested with these tests in order to set a criterion for normal stereopsis. The value of mean, mode and 75% point of these three tests were derived and compared.These three tests were also performed in 23 intermittent exotropes and 32 accommodative esotropes who showed gross stereopsis in the range of 60 to 400 seconds of arc by Titmus-fly testing. The aim was to obtain standards for clinical applicability and accuracy of these tests.This study cincludes that the appropriate criteria for normal stereopsis are less than 60 seconds of arc for Titmus-fly or Randot test, and 120 seconds of arc fot TNO test. Accurate testing for stereopsis in patients with gross stereopsis requires both Titmus-fly and Randot tests together. TNO test was inferior to the other two tests in terms of the accuracy and clinical applicability.
Depth Perception ; Humans

PURPOSE: To investigate the perception of 3-dimensional (3D) image after successful exotropia surgery and compare with Titmus stereo test. METHODS: A total of 23 children who underwent surgery for intermittent exotropia and 28 normal children were evaluated with a 3D laptop computer and Titmus stereo test. RESULTS: The mean minimal 3D scene depth level was 38.26 +/- 19.69 in the exotropia group and 33.21 +/- 16.11 in the normal group with no significant difference (p = 0.319). The mean stereoacuity was 60.97 +/- 34.23 arc sec in the exotropia group and 76.69 +/- 93.81 arc sec in the normal group with no significant difference (p = 0.444). The mean minimal 3D scene depth and mean stereoacuity showed statistically significant positive correlation in both the exotropia group (p = 0.024) and normal group (p = 0.026). CONCLUSIONS: After a successful exotropia surgery, patients can normally perceive 3D images. Better 3D image perception can be predicted if a previously established stereo test shows good results.
Child ; Depth Perception ; Exotropia ; Humans

It is known that early surgery between 6 and 24 months of age obtains better binocularity in infantile esotropia. We selected 59 patients who had infantile esotropia with onset before 6 months of age and underwent surgery at 10 years of age or less. Stereopsis was tested in 51 patients after surgery. Thirty four patients(66.7%) showed gross stereopsis. The patients who underwent surgery at 2 years of age or less, developed gross stereopsis in 80.8%. The patients who had their eyes aligned their eyes between 2 and 4 years of age, gross stereopsis was demonstrated in 64.3%, white the patients underwent surgery more than 4 years of age developed gross stereopsis in 36.3%. The younger the patients at the time of surgery, the greater the percentage of gross stereopsis was shown(p<0.05). Orthophoria(within +/-10 prism diopters) was seen in 81.3% of the patients underwent surgery at 2 years of age or less and in 59.3% of the patients underwent surgery more than 2 years of age(p>0.05). This study revealed that early surgery, before 2 years of age, yields better outcome for sensory fusion and good alignment.
Depth Perception ; Esotropia* ; Humans ; Telescopes

Authors reviewed 459 cases which had been followed up over 3 months after surgery to evaluate the incidence of consecutive esotropia and its associated factors. For every case, we investigated the age at the surgery, the methods of surgery, stereopsis, cycloplegic refractive power, the deviation difference between far and near fixation, the deviation before surgery and the results at the postoperative 1 day, 1 week, 1 month, 4 months, 6 months, 1 year and 3 years. The incidence of consecutive esotropia tended to decrease as time passed, and occurred in 21 cases[4.6%] at the last follow-up[averaging 13.1 months]. When the deviation difference between at the distance and the near fixation was above 10 delta and the results at the postoperative 1 day was overcorrection above 10 delta, with significantly higher[p<0.05] incidence of consecutive esotropia. Other factors were not statistically significant. In conclusion, the preoperative factor was the far and near deviation difference above 10 delta and the postoperative factor was the first day postoperative overcorrection above 10 delta. It is considered that the nonsurgical treatment can be desirable for the former cases, and overcorrection above 10 delta should be avoided for the latter.
Depth Perception ; Esotropia* ; Exotropia* ; Incidence

PURPOSE: To investigate horizontal image disparity in three-dimensional (3-D) perception using 3-D animations in normal control patients and patients with intermittent exotropia, anisometropic amblyopia, and partially accommodative esotropia. MATERIALS AND METHODS: A total of 133 subjects were included. Stereopsis was measured using the Titmus Stereo test (Stereo Optical Inc., Chicago, IL, USA) and a 3-D stereopsis test with a 15 inch 3-D display laptop, adjusting 3-D parameters of 0 mm horizontal disparity to 15 mm horizontal disparity. RESULTS: When compared with normal controls, the average threshold of the 3-D stereopsis test was significantly reduced for esotropia patients (p<0.001) and for anisometric amblyopia patients (p<0.001), compared to normal controls. No significant difference was observed between normal controls and intermittent exotropia patients (p=0.082). The 3-D stereopsis test was correlated with the Titmus Stereo test (Spearman's rho=0.690, p<0.001). Mean difference in stereoacuity was 1.323 log seconds of arc (95% limits of agreement: 0.486 to 2.112), and 125 (92.5%) patients were within the limits of agreement. CONCLUSION: This study demonstrated that a 3-D stereopsis test with animation is highly correlated with the Titmus Stereo test; nevertheless, 3-D stereopsis with animations generates more image disparities than the conventional Titmus Stereo test. The 3-D stereopsis test is highly predictive for estimating real stereopsis in a 3-D movie theater.
Adult ; Aged ; Amblyopia/diagnosis ; Anisometropia/diagnosis ; *Depth Perception ; Esotropia/diagnosis ; Female ; Humans ; Imaging, Three-Dimensional/*instrumentation ; Male ; Middle Aged ; *Perceptual Disorders ; Software ; *Vision Disparity ; Vision, Binocular ; Visual Acuity/*physiology

Occlusion therapy has been reported to improve the motor phase and sensory phase of exodeviations. We performed occlusion on the preferred eye in intermittent exotropia for three hours a day. Average follow-up time was 15.8 weeks. The frequency of tropic status of exodeviation was decreased in 21 cases(70%). In two cases intermitent pattern was changed to exophoria, and in one case, to exotopia. The size of the deviation angle was changed from 28.93 +/- 7.6 prism diopter(PD) to 24.03 +/- 7.9 PD(p<0.01). In 13 cases(43.3%) the size of the deviation angle decreased more than 6 PD, increased more than 6 PD in one case(3.3%), and in 16 cases(53.3%) the size of deviation angle showed no change. The preference pattern changed from monocular to alternating type in 5 cases. Stereopsis improved in 24% of the cases and did not deteriorate in Others.
Depth Perception ; Exotropia* ; Follow-Up Studies

PURPOSE: To assess the factors which are related to recovery time from overcorrection that occurred immediately after surgery. METHODS: We reviewed the medical records of intermittent exotropia patients who had undergone bilateral lateral rectus muscle recession from February 2002 to July 2004. Fifty patients who developed overcorrection of less than 20 PD on the immediate postoperative day were included in this study. Age at surgery, sex, refractive power, preoperative deviation angle, Worth 4-dot test, and stereopsis were examined, and we evaluated the correlation between these factors and recovery time. RESULTS: Thirty-six patients (72%) recovered to orthoposition within 4 weeks postoperatively. Significant correlations were found between the recovery time and poor stereopsis (p=0.02), and suppression of the Worth 4-dot test (p=0.01). There was no significant relationship between the recovery time and age at surgery, sex, refractive power, and preoperative deviation angle. CONCLUSIONS: In cases of immediate postoperative overcorrection of less than 20 PD after intermittent exotropia surgery, factors related to delayed recovery were poor stereopsis and suppression of the Worth 4-dot test.
Depth Perception ; Exotropia* ; Humans ; Medical Records