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

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

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

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

PURPOSE: This study investigated the surgical result of intermittent exotropia according to the difference between primary gaze and lateral gaze, where the extent of surgical treatment was decided by the angle of deviation in primary gaze. METHODS: The subjects of this study were 128 patients who had intermittent exotropia and were operated on by the same surgeon. Deviation angle of strabismus was checked at near and distance and primary and 30-degree lateral directions of gaze. The Worth 4 dot test and Titmus test were performed. Refixation time and axial length were measured. Either the cycloplegic refraction test or manifest refraction test was done depending on the patient's age. The extent of surgery was decided by the criteria recommended by Parks. Patients were classified into 2 groups. Group 1 included patients with 5-PD or smaller differences in the angle of deviation in the primary and lateral gaze. Patients who had differences greater than 5-PD in the angle of deviation according to the direction of gaze were classified as group 2. Clinical data were verified by Pearson Chi-square test. RESULTS: Age, sex, angle of deviation at near and distance, oblique muscle function, spherical equivalent, astigmatism, axial length, stereopsis, and refixation time did not affect the difference in the angle of deviation according to the direction of gaze. The non-fusion group showed a large difference in the angle of deviation according to the direction of gaze. The extent of surgery was determined by the deviation angle in primary gaze. Both group showed similar surgical results. CONCLUSIONS: To determine the degree of surgery needed, it is reasonable to measure the deviation angle in primary gaze for patients with intermittent exotropia.
Astigmatism ; Depth Perception ; Exotropia* ; Humans ; Strabismus

PURPOSE: The Frisby Davis Distance (FD2) Stereotest has been introduced to measure distance stereoacuity. The purpose of this study is to establish the range of normal distance stereoacuity responses on the FD2 Stereotest in a normal population. METHODS: This study comprised 65 subjects. All had best corrected vision of 20/25 or better in each eye at distance, 1.0 diopters or less of anisometropia, 8 prism diopters or less of phoria on alternate cover test at both distance and near, binocular fusion on the Worth four dot test and stereopsis on Titmus test. Distance stereoacuity was measured using the FD2 stereotest. RESULTS: The mean age of the subjects was 18.6 years (range, 3 to 59). The mean stereoacuity for distance was 15.61+/-10.41 sec (seconds of arc), and the mean stereoaucity of the subject over 10 years old was 12.98+/-6.86 sec. Results of the test-retest variability as well as of different test distances revealed no statistically significant differences. Of 60 subject with one eye closed, 11 (18.3%) of them detected the disparity of 200 sec but none could detect smaller disparity except one. CONCLUSIONS: The FD2 Stereotest is reliable test without test distance variance. The results of this study can be used as a normative data of distance stereoacuity by FD2.
Anisometropia ; Child ; Depth Perception ; Humans ; Strabismus ; Telescopes