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ARTICLE
Year : 1963  |  Volume : 11  |  Issue : 2  |  Page : 51-52

The three-mirror contact lens


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Date of Web Publication28-Jan-2008

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How to cite this article:
Weinhold H. The three-mirror contact lens. Indian J Ophthalmol 1963;11:51-2

How to cite this URL:
Weinhold H. The three-mirror contact lens. Indian J Ophthalmol [serial online] 1963 [cited 2020 Sep 24];11:51-2. Available from: http://www.ijo.in/text.asp?1963/11/2/51/38894

Ophthalmology is a field of medicine where microscopic investigations of the living tissue are part of the routine method. This examination is carried out with the slit lamp viz; a com­bination of a horizontally mounted stereomicroscope and a swingable light source producing a light beam with a slit-shaped cross section.

Only the anterior section of the eye (cornea, iris, lens) is accessible to direct observation with the stereo­microscope of the slit-lamp because only objects can be observed which lie in the object plane of the microscope, i.e., approx. 10 cm before the front lens. To observe the fundus of the eye (retina etc.) which is projected by the optical system of the eye into the distance, additional aide are therefore required with the aid of which the fundus oculi is projected at a distance accessible to the stereomicroscope. For this purpose highly positive or negative lenses or contact lenses with a suitably shaped surface are used.

The new Zeiss Three-Mirror Con­tact Lens, which in its basic design corresponds to the GOLDMANN three-mirror contact lens, is such an aid for the observation of the fundus (and the anterior chamber angle) through the stereomicroscope. Ex­teriorally it is a wedge-shaped device [Figure - 1] of almost 2.5 cm length, which can be attached to the eye with a corneal and scleral portion and the outer surface of which is a plane glass surface.

Inside, the contact lens contains a truncated cone of glass on the side of which three-mirror surfaces are ground at different angles.

[Figure - 2] illustrates the mode of action of this lens. When looking through the central parts (o) of the three-mirror contact lens the central part of the fundus oculi can be observed [Figure - 2]b. Due to the fact that in place of the air a lens with a refractive in­dex of approx. 1.5 is located in front of the cornea, the refractive power or the cornea is neutralized and that of the lens compensated, so that the image of the fundus oculi does not lie at infinity but approx. 3 cm behind the plane boundary area of the glass. When using the mirror 1 [Figure - 2]c the same applies in principle but, by de­flecting the optical path, it will be possible to observe those parts of the retina that lie outside of the centre.

The mirror 2 [Figure - 2]d accordingly serves for the examination of the periphery of the retina.

In addition to these mirrors, which permit the examination of the peri­pheral parts of the retina when the patient looks straight ahead, provision is also made for a gonioscopic mirror 3. Normally the rays emerging from the anterior chamber-angle are totally reflected at the cornea so that this part of the anterior section is not accessible to observation. By attach­ing the contact lens the total reflection is avoided and it is possible to look in­to the anterior chamber-angle through mirror 3 [Figure - 2]e.

This aid is used in the normal way by attaching it on' to the anaesthetised cornea of the sitting patient. During the examination the lens is held with one hand and brought into the requir­ed position by turning it accordingly.

In conclusion it should be mention­ed that by using glass for the optical parts the clarity of the image is main­tained even when frequently cleaning them as the glass has a high wiping resistance if compared with synthetic material which may also be used for such lenses.


    Figures

  [Figure - 1], [Figure - 2]



 

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