The horizontal Lang two-pencil test, a subjective test which could be easily performed, was able to detect all the patients with stereopsis. It was interesting to note that it also detected stereopsis in four of the 18 patients who otherwise had no measurable stereopsis on TNO and Randot. Visual acuity was assessed using the Snellen’s visual acuity chart. Bagolini glass test was used to assess binocularity and fusion consists of lenses with striations which are at right angles to each other.
This test was used to determine racial identity in South Africa during the apartheid era, distinguishing whites from coloureds and blacks. The test was partially responsible for splitting existing communities and families along perceived racial lines. Pencils are now an important part of South African cultural heritage and a symbol of racism. If you publish one on the cloud, it can immediately be taken, anywhere in the world. Online exams can be built with tools for zoom, color contrast changes, automated text-to-speech, and other things to support accessibility. This is especially true in areas of the world that do not have the internet bandwidth or other technology necessary to deliver internet-based testing.
Can’t wait for your bra?
However, in those without stereopsis, all but one patient (false positive) showed absence of stereopsis on the synoptophore. Evaluation using the horizontal Lang two-pencil test showed that all the patients with stereopsis were picked up correctly and there were four false positive results. Examination using the Bagolini striated glass test for binocularity showed that all the patients with stereopsis had binocular single vision. However, 14 of the 18 patients with no measurable stereo-acuity also showed presence of binocular single vision (data not shown). The study was to compare any level of measurable stereo-acuity on the two stereo tests, namely TNO and Randot, with the gross stereopsis detected by the horizontal Lang two-pencil test. Therefore, comparison of patients with random dot versus local stereopsis was not performed.
However, this point has not been proven and a comparative evaluation between the vertical and horizontal pencil test cases has not been done. Evaluation using the synoptophore is more complicated, and we found it to be not as sensitive as the horizontal Lang two-pencil test. A possible reason could be the younger age group of our subjects who may have found the test trying and not easy to perform.
Horizontal lang two-pencil test as a screening test for stereopsis and binocularity
The level of stereo-acuity was evaluated using TNO and Randot stereo tests, which are based on the Random dot stereograms. They contain no information about the shape or nature of the object hidden in the visual noise of random dots. Only when the images from the right and left eye are combined at the neural level and the object is seen in depth does recognition take place. Some advantages of paper-and-pencil testing include students having familiarity with the system, development of a social connection between learners, exemption from technical glitches, and affordability. Some schools don’t have the resources and pen-and-paper assessments are the only option available. First, we have not attempted to compare the horizontal Lang two-pencil test with the popularly performed vertical test, hence our assumption that the horizontal test contains less monocular cues could not be proven.
Clinical evaluation included visual acuity testing, refraction, ocular movement assessment, cover test, and prism bar cover test (PBCT) to determine the amount of deviation. Sensory status examination for binocularity and fusion were performed using the Bagolini striated glass test (a routinely used test), the three circles test on TNO and the R and L test in the Randot booklet. Stereopsis was assessed by the synoptophore, horizontal Lang two-pencil test, TNO and Randot test booklets. TNO or Randot are routinely used stereo tests to determine level of stereo-acuity.
Pencil test (breasts)
Sensory status examination including binocularity and stereopsis were evaluated with Bagolini, Titmus test and the Netherlands organisation for applied scientific research (TNO), Randot, synoptophore and horizontal Lang two-pencil test. Table 3 shows the predictivity of the synoptophore and horizontal Lang two-pencil test in comparison to TNO and Randot as a test for stereopsis. In Table 4, binocularity was compared between the three circles’ test on TNO, R and L test on Randot and Lang two-pencil test taking Bagolini striated glass test as the gold standard for binocularity. As can be seen in the Table, Lang pencil test being a test to detect gross stereopsis, shows 100% specificity for binocularity. Performance of the subjects on the Bagilini striated glass test and the four stereo tests is summarized in Table 2.
A subgroup analysis was done for the subjects in Group 1 between those with and without stereopsis. There were 26 subjects with stereopsis (25 had measurable stereo-acuity levels and one had only gross stereopsis) and 18 without stereopsis. Of the 26 with stereopsis, two were missed on the synoptophore. One of these patients had stereo-acuity of 480 arc seconds on the TNO and the other had stereo-acuity of 400 arc seconds on the Randot.
Pencil test (South Africa)
This was a cross-sectional study evaluating the horizontal Lang two-pencil test in acquired strabismus and normal subjects after approval from the Institutional review board of our Institute. The subjects were enrolled from the squint clinic and outpatient department of our Institute. Any subject with vertical strabismus more than 5 prism diopters (PD), or with intermittent deviation or any heterophoria, or not willing to participate in the evaluation was excluded. Patients with intermittent strabismus were excluded because it is believed that they may have some fusional component. The subjects were divided into two groups based on the amount of deviation; Group 1 with an angle of deviation less than or equal to 8 PD, and Group 2 with deviation greater than or equal to 10 PD. The criteria for normal subjects were a BCVA of 20/20 with no significant anisometropia, and who were orthophoric.
The subjects in the group with smaller deviation showed better performance on all the four stereo tests and over 90% demonstrated presence of fusion. When compared to TNO and Randot for determining presence of stereopsis, the horizontal Lang two-pencil test demonstrated sensitivity of 100% and 83.9%, specificity of 77.8% and 73.7%, and negative predictive value of 100% and 100% respectively. It also showed 100% specificity as a test for binocularity when compared with the Bagolini striated glass test. The TNO stereo test was performed by placing the plates at a test distance of 40 cm squarely in front of the patient, wearing spectacle correction if using one. The test consists of seven plates, the first three of which were used for screening to detect the presence of gross stereopsis.
Traditional methods of hand-scoring paper tests are slow and labor-intensive. Another advantage of paper exams is that they can often work better for students with special needs, such as blind students which need a reader. Offline exams have been a stepping stone towards the development of modern assessment models that are more effective. We can’t ignore the fact that there are several advantages of traditional exams.
The last three plates on the other hand were used to quantitatively assess stereo-acuity in the range of 15 to 480 sec of arc. Each plate consisted of four squares, within which was a circle with a ‘pie’/ piece missing. The normal value for stereo-acuity was considered ≤60 sec of arc. Eighty-four strabismic subjects divided into two groups based on the amount of deviation, and 40 normal subjects were studied.
Pencil Hardness Test
It was performed by keeping a pair of the striated glasses in front of each eye, and the subject was asked to fixate on a punctate light source. The possible responses were a) symmetrical cross response b) asymmetrical cross response c), single line response, and d) cross response with a central gap in one line. Responses ‘a’ and ‘b’ indicate binocularity while response ‘c’ indicates suppression. The central suppression response ‘d’ indicates either a fixation point scotoma (with manifest deviation and anomalous retinal correspondence) or foveal scotoma (with orthophoria and normal retinal correspondence). The three circles test on TNO and the R and L test in the Randot booklet was explained together with the respective tests. Horizontal Lang two-pencil test, an easily performed test with a high sensitivity and negative predictive value can be used as a screening test to detect gross stereopsis and binocularity.
- The study was to compare any level of measurable stereo-acuity on the two stereo tests, namely TNO and Randot, with the gross stereopsis detected by the horizontal Lang two-pencil test.
- First, we have not attempted to compare the horizontal Lang two-pencil test with the popularly performed vertical test, hence our assumption that the horizontal test contains less monocular cues could not be proven.
- However, the paper-and-pencil testing does have a number of shortfalls.
- In the pencil test, a pencil is pushed through the person’s hair.
- Over 90% of subjects in the group with a smaller angle of deviation, and all normal subjects showed presence of fusion, whereas only 30% of subjects with larger deviation had fusion.
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