Introduction
Retinoscopy is a test that establishes an objective measurement of a patient's refractive state. In dynamic retinoscopy, the subject fixates on an object at close distance with both eyes. It is different from the static retinoscopy where the patient instead fixates on a distant object. The test allows for the assessment of accommodative ability, that is, how the eyes are able to adjust their power to maintain focus. The accommodative ability can be lag, lead, or normal.
The test can detect a refractive error, a problem where the eye is unable to focus light accurately on the retina. The different types of refractive errors include near-sightedness, far-sightedness, amblyopia, and astigmatism. Dynamic retinoscopy is therefore an objective refraction method.
A doctor may indicate a dynamic retinoscopy for the following reasons:
- To ascertain suspected causes of vergence or accommodative dysfunctions which are also used to determine whether the patient is over or under corrected.
- To identify whether a seeing -eye irrespective of its degree of vision has any accommodative ability.
- To help decide amblyopic therapy - Amblyopia implies subnormal vision and this procedure allows the establishment of an appropriate remedy.
- To help determine cycloplegia's adequacy - While cycloplegic agents' use is widespread, a clinician can use dynamic retinoscopy to assess lag of accommodation and determine the necessity of cycloplegic retinoscopy.
- To reveal the stability or degree of fluctuation of the accommodative system.
Also Known As
- Near retinoscopy
Types
Dynamic retinoscopy is conducted through various techniques, including:
- Nott’s retinoscopy
- MEM (monocular estimation method)
- Bell retinoscopy
- Book retinoscopy
Before the Procedure
Before performing the test, the preparations and expectations are as follows:
- The doctor should ensure the beam is completely expanded. For most retinoscopes, this will mean adjusting the sleeve down.
- The phoropter should be level and the pupils centered. The doctor should maintain a position of about 15 degrees from the line of sight.
- The patient’s eyes should stay fixated on the object and not the light. The patient should also let the eye specialist know if at any point the target is obstructed.
Procedure
- Nott Method
The target is a block of 6/6 letters positioned 16 inches from the patient. It is held in place by the doctor, by an assistant or on a scale. The patient must wear their distance correction lenses, and they see the target binocularly. The retinoscope is placed beside the target, and the reflex movement is observed.
- Monocular Estimate Method (MEM)
The target is a series of cards with a central aperture attached to a retinoscope. The cards have letters with varying sizes arranged around the opening. The patient is required to keep the targets clear, and the examiner observes the reflex. Lenses are used to neutralize the reflex, rather than moving the retinoscope back and front. If the movement is with, add “+ lenses”; if it is against add “- lenses” until a neutral reflex is achieved.
- Bell Retinoscopy
The test requires a 3-D observing target and a small, greatly reflective bell hanging from a cord. The examiner holds the string with the dangling bell while moving it closer to or further from the patient at a speed lesser than 2 inches/second. The retinoscope is placed at a still position about 20 inches, where the patient observes the target as the clinician notes the reflex direction. The target is drawn nearer to the patient, and the movement shifts from "with" to "against." The target is shifted from the patient until the examiner observes a “with” motion.
- Book Retinoscopy
It is also known as Getman retinoscopy. The patient is given reading material, and retinoscopy is performed as the subject reads aloud. Information is collected in real-time with a task close to their normal work situation.
The response levels can be at either free reading level (it is desirable, and reflex varies from neutral to with), instructional level (more demanding than the free level and reflex varies fast against motion) or frustration level (although the subject is focused, there is an improper interpretation of information).
Risks & Complications
Dynamic retinoscopy can be challenging among young children. For instance, it is inconvenient to perform Nott retinoscopy using a fixed target in a usual clinic setting without an assistant. Withdrawal of an examiner can cause a distraction to the patient, and thus the retinoscopic reflex observed from a distance becomes hard to evaluate if lag is high.
In the case of an inattentive child, it is hard to introduce MEM lenses in a manner that does not influence accommodation.
Outcome
- Nott Method
If the direction is against, the subject displays over accommodation, and the retinoscope ought to be shifted towards the patient until attainment of a neutral point. If the movement is with, the subject exhibits under accommodation. Therefore, the retinoscope is drawn away from the patient until a neutral position is achieved. The distance between the neutral point and the target is converted to diopters. The resulting dioptric value is the magnitude of the lead (for the former) or lag (for the latter) of the accommodation.
- Monocular Estimate Method (MEM)
If the ultimate power is in "- lenses," the subject is over accommodating, meaning the patient has a lead of accommodation. If the ultimate power is in "+ lenses," the patient is under accommodating, meaning the patient has a lag of accommodation. An accommodation range of +0.50DS to +0.75DS is considered normal.
- Bell Retinoscopy
The lag of accommodation is measured by the length between the target and the retinoscope when there is a variation in motion. Eye movement controlled can be assessed by judging the extent to which the bell can be fixated. Eye-hand coordination, on the other hand, can be evaluated by asking the patient to touch the bell during the process.
- Book Retinoscopy
Reflex color is bright and white when words are understood, pink and slightly dim when the patient struggles to comprehend a passage, and dull or brick-colored when a patient cannot read a passage.
