Introduction
PERRLA is an acronym giving an incomplete description of the pupillary function. It expands into pupils equal, round, and reactive to light and accommodation. The psychomotor test is performed to assess the motor functions of the pupil of the eyes.
What Does the PERRLA Test Assess in the Pupil?
The PERRLA test is a psychomotor test that assesses the following characteristics of the pupil.
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Size.
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Shape.
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Pupillary reaction.
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Pupillary accommodation-convergence reflex.
What Is a Pupil of the Eye?
The pupil of the eyes is the central opening or black aperture present in the center of the colored part of the eye (iris). It helps focus the light entering the eye towards the retina at the back of the eye. It also regulates the intensity of light entering the eyes.
What Is the Primary Function of the Pupil?
The pupil of the eyes primarily helps control the amount of light entering the eyes by pupillary constriction and accommodation. Also, it helps in focusing on the object of interest.
What Are the Characteristics of the Pupil of a Normal Eye?
The pupils of a normal eye show the following characteristics on examination:
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The pupils of both eyes should be equal in size.
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The pupils of both eyes are round in shape.
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The pupils are reactive toward the type of light entering the eye.
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The pupil shows accommodative reflex capacity while seeing nearby and far away objects.
What Are the Factors That Govern the Size of the Pupil of the Eyes?
The size of the pupil is mainly governed by the circumferential sphincter muscles and dilator muscles of the iris. The muscles are innervated by both the parasympathetic and sympathetic nervous systems. Therefore, injury to the power or the nerve leads to a change in the size of the pupil.
What Is the Mechanism Involved Behind the Pupillary Reflex to Light?
The pupillary light reflex or the photo-pupillary light reflex regulates the pupil's diameter in response to light. It is controlled by the cells (rods and cones) present in the retina. In addition, the retinal cells regulate pupillomotor activity. As a result, the pupils constrict in case of bright light. There is dilation of the pupil in darker situations. Pupillary reflex also helps regulate the intensity of the light entering the eye.
What Are the Factors That Determine Pupillary Reaction to Light?
The condition of the iris determines the extent of constriction in the pupil, the color of the iris (brown iris contracts less than blue), and the patient's age. For example, the iris sphincter does not work correctly in older people, and there is a diminished reaction to light.
How Does the Accommodation Reflex of the Pupil Work?
The accommodation-convergence reflex of the pupil helps focus the nearby and faraway objects. It is controlled by the second cranial nerve and ciliary muscles. Therefore, the accommodation reflex of the pupil is mainly responsible for focusing on the things of interest.
The following mechanisms bring about the accommodation reflex -
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Lens thickening.
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Pupillary constriction.
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Convergence of the eyes inwardly.
How Is the PERRLA Test Performed?
The examiner performs the PERRLA test using the following steps:
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First, the doctor checks the pupil of the eyes in a dim-lit room.
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The doctor asks the patient to focus their eyes on a distant object.
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The pupils of the patients should be in a semi-dilated condition.
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Following this, the doctor shines the flashlight on the yes, one at a time.
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To measure the size of the pupil, the doctor first focuses the light on the bottom of the face and then slowly moves upwards to the patient's eye level. The examination room is darkened while examining.
How Is the PERRLA Eye Assessment Form Written?
After examining the patient's pupil, the assessment of the pupil is written in a separate form.
The grading of the pupillary reaction to light, pupil accommodation, size, and shape, are written in two separate columns for both eyes.
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Firstly, the size of the pupil in both eyes is measured. The average size varies from 2-4 mm in bright light and 4-8 mm in the dark for adults.
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The shape of the pupil is noted, whether it is round or not.
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The pupil's light reaction and accommodation to light are given a grade from +1 to +4. Usually, the pupils constrict in bright light, dilate in the dark, and are graded accordingly.
What Is the Clinical Significance of PERRLA Assessment of the Pupil of the Eyes?
The primary significance of PERRLA assessment is to detect the various conditions of the pupil associated with the abnormality in the pupil's size, shape, light reaction, and accommodation.
The PERRLA assessment helps in diagnosing the following conditions:
1. Diseases With Defective Size of the Pupil Are -
2. Diseases With Abnormal Shape of the Pupil Are -
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Coloboma.
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Post-cataract surgery.
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Injury.
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New blood vessels formation.
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Rare brain disease.
3. Diseases With Defective Pupillary Reaction to Light Are -
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Optic neuritis.
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Optic nerve damage.
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Retinal infection.
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Glaucoma.
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Third cranial nerve palsy.
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Overactive ciliary muscles.
4. Conditions With Defective Accommodation Reflex of the Pupil Are -
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Infections of the optic nerve.
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Injury.
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Macular degeneration.
What Are the Shortcomings of the PERRLA Assessment of the Eye?
The PERRLA test, though helpful in detecting many of the inappropriate causes related to the functions of the pupil, has a few shortcomings, such as:
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First, it omits the critical clinical characteristics of the pupil of the eye.
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Second, the PERRLA test fails to pinpoint the actual cause of the disease.
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It fails to assess the actual size of the pupil.
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It is unable to determine the exact shape of the pupil.
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The extent of pupillary constriction and the speed of contraction of the pupil is also not wholly determined.
Conclusion
The PERRLA test of the eye is used to assess the various psychomotor functions of the pupil. Though it has a few shortcomings, it is an inexpensive method for determining the underlying conditions related to the abnormality of the pupil of the eyes.
