Set of 1 & 2 CHF 230
Last a lifetime.
In Ontario shortage of Ophthos interested in Strabismus. OHIP payments poor. Retiring Lady Ophtho. who specialized in Strabismus could not give away her busy practice at Toronto 123 Edward St Medical building
Toronto "Hosp for Sick Children" has an OHIP-paid ORTHOPTIC dept,. (odd name: why include "Sick')
There are two Specialists interested in Strabismus.
Prof Stephen Paul KRAFT MD(Tor.1978) FRCPC(1982) The only Canadian in the USA Assn for Research in Strabismus. stephenkraft@sickkids.ca
Asst.Prof David Royce SMITH MDCM (McGill 1964) FRCPC (1969) drsoffice@plink.net
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LANG-STEREOTEST
Development and characteristics:
The LANG-STEREOTEST was developed by the Swiss
ophthalmologist Joseph Lang in the beginning of the eighties. The
easy-to-use test is applied for the early detection of problems in
stereoscopic vision in children and infants, but also in adults. Since
many years, the test has been very much estimated by ophthalmologists,
paediatricians and doctors working in the primary health care or in
prevention. Two versions are available (LANG-STEREOTEST I and II) which
only differ in the type of stereoscopic objects to be recognized. The
LANG-STEREOTEST II additionally contains a picture that can be
recognized with only one eye (a star). The test-plates are solid and can
easily be carried around due to their handy postcard-size. These are
distributed together with a fitting case, a brief instruction as well as
a detailed test-description in several languages.
The Importance of stereopsis:
Stereopsis or depth perception can be characterized
as the highest degree of binocular vision. It therefore represents one
of the most important partial functions of the human visual sense. In a
limited extent, stereoscopic vision is actually possible with only one
eye, for example due to perspective and shadow effects or parallel
displacement, as well as with certain forms of strabismus (with the
so-called anomalous retinal correspondence which occurs when
non-corresponding retinal points have the same sense of visual
direction). However, a completely missing or limited stereopsis can lead
to severe handicaps in many life-domains and professions. This is a
reason why this function should already be regularly examined in
children and later within the education of jobs requiring an accurate
stereoscopic vision.
Functional principle of the LANG-STEREOTEST
The LANG-STEREOTEST for the first time combines two
functional principles of stereograms: The random dots of Julesz and the
grid of cylinders of W.R. Hess. The random dots of Julesz are applied in
different stereograms using polarized glasses or the red-green-glasses.
Seen with only one eye (monocular vision), these stereograms do not
show any shapes, while, upon binocular inspection, figures, typically in
different depths, can be seen.
Grids of cylinders were invented by the Swiss
ophthalmologist and physiologist W. R. Hess (Nobel Prize in 1949) in
1912. The images of the two eyes are separated by a system of tiny
parallel cylindrical strips. Under each cylinder, there are two tiny
strips of picture: one can only be perceived by the right, the other
only by the left eye.
Particularities in comparison to other stereo-test methods:
In contrast to the more traditional methods for
examination of stereopsis, the Lang-Stereotest requires no glasses and
the eye movements of the patient can be much better observed by the
examiner, thanks to the first-time combination of the two technologies
mentioned above. Observing the patients eye-movement during testing has
been noticed to be of particular importance in small children: once the
child has recognized the different stereoscopic figures that are shown
on the test-plate, he subsequently will start to look repeatedly at
these figures.
Other common, so-called haploscopic test-procedures,
such as the Titmus-test are based on polarization and therefore require
special glasses. The TNO-test uses the red-green-dissociation and hence
needs corresponding red-green-glasses as well. With the LANG-STEREOTEST
however, the dissociation in haploscopic pictures is ensured by the
cylinder gratings on the surface of the test-plate.
Furthermore, due to the application of the random
dots and the lacking of picture-outlines in the LANG-STEREOTEST, as well
as in similar test using this principle (e.g. a version of the
Randot-test), all monocular stereoscopic stimuli are completely
eliminated. It is just the disparity of the figures represented, that
generates a perception of depth and hence enables a precise perception
of the shapes. Since primarily children are investigated, three objects
have been chosen which are already common in this stage of life. The
three objects – in the LANG-STEREOTEST I a cat, a star and a car, in the
LANG-STEREOTEST II an elephant, a car and a moon – differ in disparity
and perceived distance, the cat respectively the elephant being the
closest.
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