Prismatic spectacles

Strabismus is the pathology when the optical axis of one or both eyes deviates from the common point of fixation. Strabismus is accompanied with binocular vision disorder and a significant decrease in visual acuity of the squinting eye.

There are two main ways of strabismus treatment - therapeutic (instrumental) and surgical.

The ophthalmologists of the SVIT ZORU Clinic use new method to treat strabismus - prismatic correction (prism eyeglasses are used in the treatment). This method allows to cure small-angle strabismus without surgical intervention.

Wearing prism glasses is also the main pre- and post-operative phase, which facilitates binocular vision development.

Let us consider the essence of the method.

1. Convergent strabismus.

Convergent strabismus

AB – optical axis of the left eye.
СD – optical axis of the right squinting eye.
Common fixation point is absent.

1-a. Convergent strabismus compensated by a prism.

Convergent strabismus.

АВ – optical axis of the left eye.
СВ – optical axis of the right squinting eye, broken by a prism.
The prism deflected the optical axis of the right eye towards the base, point D changed its position and coincided with point B, which became a common point of fixation of both eyes.

2. Divergent strabismus.

Divergent strabismus

EF – optical axis of the left eye.
КM – optical axis of the right squinting eye.
Common point of fixation is absent.

2-а. Divergent strabismus compensated by a prism.

Divergent strabismus

EF – optical axis of the left eye.
KF – optical axis of the right eye, broken by a prism.
The prism deflected the optical axis of the right eye towards the base, point M changed its position and coincided with point F, which became a common point of fixation of both eyes.

The scheme shows that prismatic correction of convergent as well as divergent strabismus did not correct this disorder. It compensated and leveled it, deflected the optical axis, shifted the image on the retina of the squinting eye and above all it ensured bicentral projection of a single object of fixation at the existing angle of squint and prepared the patient for orthoptic, diploptic and, if necessary, surgical stage of treatment. Therefore, the prism involved the squinting eye in the visual action, thereby ensuring the work of the triangle:

For a long time technical difficulties curbed the widespread use of prisms for strabismus: eyeglass lenses with large prismatic effect were heavy, inaesthetic and had significant aberrations.

Owing to discovered Fresnel micro-prism elements, the possibility to introduce prisms of up to 40 prism diopters, made it possible to use eyeglasses for strabismus treatment in ophthalmic practice. Since it is impossible to purchase Fresnel prisms, the methodology for their production was developed in Ukraine, which offered the possibility to use prism correction for strabismus treatment (a set of prism compensators KK-42).

By using this set, an ophthalmologist determines the type of strabismus and refractive error. Based on the results of examination a prescription will be written for production of prismatic spectacles.

Prismatic spectacles

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