The prism eye test - it’s like a detective for your eyes. This diagnostic test uses specialized prism glasses to check if the eyes are correctly aligned or not. There could be signs of frustration associated with double vision, misalignment, and more.

Imagine the frustration of driving, playing sports, reading, or working when your eyes are constantly at odds. These everyday activities can become stressful if your eyes aren't aligned properly.

Get this clinical procedure to figure out the horizontal and vertical deviations of the eyes. But many prism eye tests can be beneficial for your case. We can help you figure out that case today.

Understanding Prism Lenses and Eye Tests

Prism lenses are corrective lenses that are triangular. The lenses lack standard focusing power and do not correct any refractive errors, but are only used for eye alignment and coordination.

Types of vision problems addressed by prism lenses include double vision (diplopia), strabismus, binocular vision dysfunction (BVD), convergence insufficiency, and individuals with strokes, migraines, and injuries.

Prism lenses are designed to correct vision problems. It is made of plastic or glass. It is different from regular eyeglasses or used as a temporary solution, such as Fresnel prisms, which are thin vinyl stickers placed on existing lenses.

The Prism Eye Test: Process and Types

Today we will discuss the common tests used to evaluate the need for prism lenses. But before that, we show familiarity with the types of prism configurations in tabular presentation.

1. Krimsky Eye test

The Krimsky test is to assess strabismus and misalignment of the eyes. The examiner of the Krimsky test is placed in front of the deviating eye to correct the deviation of the corneal light reflex.

Doctors look to see how strong a prism needs to be to bring the light reflex of the deviating eye onto the pupil. Strabismus can lead to various visual problems, including double vision and impaired depth perception.

By quantifying the degree of misalignment, the Krimsky test helps eye care professionals determine the appropriate course of treatment, which may include corrective lenses, vision therapy, or surgical intervention. The main procedure of the test is:

• The adjustment of prism strength.
• Continue until the corneal light reflex on the cornea) of both eyes.
• Light reflection aligns centrally on the pupil of the deviating eye.

The test requires only that the patient fixate on the light, being entirely objective; otherwise, it is useful in testing small children. It is quicker to perform than the prism cover test.

Procedures of the Krimsky Eye Test

• The test is conducted in a well-lit environment with a light source.
• The prism is placed strategically in the test to check the alignment of the eyes.
• PRT is particularly useful for patients with blind or deeply amblyopic eyes.
• Krimsky described the prism bar reflex test (PBRT) as a practical method of testing the angle of deviation and misalignment of eyes.
• Krimsky Eye Test is done both with and without centric fixation on the prism bar or pen torch.
• The prism is positioned in front of the normal, fixating eye.
• The prism's strength is adjusted until the corneal light reflex is centered in the deviating (squinting) eye.
• To achieve the power of the prism, the required centering is equal to the amount of eye deviation.
• The examiner should use only one eye to observe the corneal reflex to prevent parallax errors.

Preparation for the Krimsky Test

• Ensure a well-lit environment for optimal visibility.
• Gather a prism bar or pen torch as the light source.
• The PRT is particularly useful for patients with blind or deeply amblyopic eyes.
• We test the fundamental principle of Hering's law throughout the procedure.
• Prepare all tools and equipment required for enhancements of visual alignment and stereo acuity.

Limitations of the Krimsky-Prism test

The Angle kappa is included in the measurement, so the readings are not exactly accurate; it's just a calculated estimation

The test can't be performed for distance fixation since position head requirements to obtain accurate observation prevent the patient from seeing the fixation light.

2. Prism Bar Cover test

The prism bar cover test is a fundamental eye procedure to check your eyes' ocular alignment and strabismus. We help you detect both tropia and phoria, two types of strabismus, with the initial setup.

Step 1: Arrange the initial setup

Step 2: The examiner covers one eye with a prism bar occluder while observing the uncovered eye. Before the next step, know how you can have proper misalignment and deviation testing through this.

Step 3: Identify the case of strabismus, whether it is tropia or phoria.

• When the uncovered eye moves to fixate on the target, you may have tropia.
• If there is no movement, the patient may have phoria (eyes that misalign when closed).
• Through PBCT, the numerical value of the degree of strabismus can be tested.

Tropia is a constant misalignment of the eyes when one or both eyes turn inward, outward, up, or down. It's often referred to as "crossed eyes" or "squint." The examiner puts an appropriate prism in front of the deviated eye based on initial findings to continue with the testing of strabismus in your eyes.

3. Howell test for eyes

The Howell Test is the test through which the degree of phoria (latent strabismus) at near and far distances is analyzed. In the Howell test, the Howell card and prism (a 6-diopter prism) are used to perceive double images.

The Howell testing procedure is initially set, with the patient positioned to view the Howell Card at a specified distance (usually 33 cm for near testing)

Let's explain the visual experience in the Howell Test.

• A 6-diopter prism is placed over one eye.
• Check whether a patient perceives two or more images on the Howell card.
• This dislocation allows clinical evaluation of the misalignment of the eyes.

At the same time, to check the diagnostic information, we look at the arrow movement on the scale of the Howell card.

To improve binocular coordination and reduce symptoms in case of misalignment in phoria (when one eye is closed), the Howell prism eye test is beneficial. When one of the eyes is not actively used for fixation, the patient with latent misalignment diagnoses these two issues.

• Right hyperphoria: the right eye tends to deviate upward
• Left hypophoria: the left eye tends to deviate downward

4. Maddox rod test

The Maddox rod test also used a prism bar for the evaluation of strabismus and latent deviation. It is primarily focused on seeing deviations when the eyes are open.

• On a dim light, when patients have comfortable seating, they are made to focus on a light source at a distance of 6 meters.
• The observation can either indicate the red streak, which means this is normal, or not the warning sign as always.

Benefits of Prism Eye Test

• Prism tests help optometrists assess how well the eyes work together.
• With the diagnosis of a degree of misalignment of eyes, you can have tailored eye treatment plans.
• Prism lenses may take time to adapt but have great results in improving eye strain and discomfort for those with squint eyes.
• The eye test facilitates effective treatment of depth perception issues.
• Many patients have reported alleviation of fatigue after the test.
• One can effectively recover from neurological issues and eye injuries.

Conclusion

In this blog, we have discussed the prism eye test in different circumstances. We tried the eye test, where a 6-diopter base-up prism is placed over the right eye and his latent alignment and ability to converge are tested. Contact Vision Concern if you have any related inquiries about your eyes. You can easily book your appointment online for expert check-ups at one of the best eye clinics in Kathmandu. Tune into more interesting eye tests and care tips.