Treating with Prism

TARIQ AL FAYAD. MB.OPTOM @Level

What is STRABISMUS

Crossed eyes, or strabismus, is a condition in which both eyes do not look at the same place at the same

time. It usually occurs in people who have poor eye muscle control or are

very farsighted.

Strabismus is classified by the direction the eye turns:

Inward turning is called esotropiaOutward turning is called exotropiaUpward turning is called hypertropiaDownward turning is called hypotropia.

How is strabismus treated?

Fresnel prisms  These special lenses have a prescription for

prism power in them. The prisms alter the light entering the eye and reduce how much turning the eye must do to view objects. Sometimes the prisms can

eliminate the eye turning.

Anisometropia

• They will complain of double Vs while reading• Due to prismatic effect• To correct them, Vertical prisms are used in

the lower portion of one lens• prisms are referred to as slab-off or reverse-

slab prisms

• The slab-off prism is placed on the more minus or less plus lens,, (adds base-up prism)

• The reverse-slab prism is placed on the more plus or less minus lens, (adds base-down prism)

The slab-off prism

Childhood Cranial Nerve Palsies (Third, Fourth, and Sixth Cranial Nerves)

• early treatment is important to prevent amblyopia.

• Prisms may be used for smaller amount in order to maintain binocular function

• Fresnel prisms is recommended prior to grinding prisms into the child’s lense

• if prism therapy fails, surgery should be considered.

Prisms for Enhancing Communication

• For patients with no useful vision in the deviated eye, prisms can be extremely helpful in improving the appearance of the eyes and facilitating the patients’ communication and interaction with others by alleviating difficulties with eye contact.

• A prism held opposite the direction of a correcting (ie, base-in for esotropia and base-out for exotropia)

Homonymous hemianopia

A homonymous hemianopia is the loss of half of the field of view on the same side in both

eyes.

Homonymous hemianopia

• Prisms may be used in patients with homonymous hemianopia to bring images from an area within the visual field.

• Very high prism powers are required, which can create cosmetic problems/ confusing visual environment in which objects may appear and disappear from view unexpectedly.

Nystagmus with head turn

• Patients with a head turn to compensate for nystagmus can benefit from yoked prisms.

• high prism powers which may lead to decrease in visual acuity.

• Prescription of bilateral yoked prisms, with base in the same direction as the head turn, can keep the patient’s eyes in an eccentric null position while lessening the head turn.

Head/neck position problems

• patients with severe ankylosing spondylitis, may benefit from prisms.

• base-up “yoked” prisms can allow for improvement in straight-ahead vision.

 convergence insufficiency

• To resolve convergence, base-out prisms are used which force the system to work harder to converge.

• Base-in prisms can be used to artificially align the eyes for reading; however, their use, patient will develop stronger convergence on their own.

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