Objective Refraction Techniques: Retinoscopy
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Title: Objective Refraction Techniques: Retinoscopy
Authors: Cori Jones, OD; David Meyer, OD, FAAO
Date: 6/30/21
Keywords/Main Subjects: Refractive error, retinoscope, how to perform retinoscopy
Description of Case:
Overview: This paper outlines retinoscopy as a technique in clinical refraction. It highlights:
- Fundamentals of refractive error
- Optical principles of retinoscopy
- Parts of a retinoscope
- Retinoscopy setup
- A step-by-step guide for performing retinoscopy
- Troubleshooting tips
Introduction
Retinoscopy is an important skill to master in the field of eye care. It provides an objective measure of refractive error, making it extremely useful in pediatric exams and special populations.[1] Unlike the objective measure provided by an autorefractor, retinoscopy does not require the patient to focus on an image for several seconds while keeping completely still. Additionally, retinoscopy gives clues about the patient’s accommodation, avoiding the over-minusing errors that often result from autorefraction. This technique can also provide clues to ocular pathology such as keratoconus, corneal disease, and lens opacities.
Since patient input is not required, retinoscopy is often used for infants, children, patients displaying poor cooperation, adults with developmental delays, and during exams where verbal communication is hindered by language barriers. Many eye care providers perform retinoscopy on every patient as an alternative to autorefraction.[2]
When performed correctly, retinoscopy provides a quick, reliable, and accurate measure of refractive error for any type of patient.[3]
Fundamentals of Refractive Error
To review, emmetropia describes an uncorrected eye that focuses incoming parallel light exactly on the retina to provide a clear image. Hyperopia, or farsightedness, occurs when incoming parallel light focuses behind the retina because of a short eyeball or too little power within the uncorrected eye. Myopia, or nearsightedness, occurs when parallel light focuses in front of the retina due to a long eyeball or too much power within the uncorrected eye. Astigmatism results when the refractive error differs in magnitude between perpendicular meridians within the eye.
The far point of an eye is defined as “the point in space conjugate to the retina when the eye is not accommodating,” e.g. the farthest point at which the eye can clearly see an object without accommodating.[4] It can be found mathematically by solving for the inverse of the refractive error. Far point can also be found by ray tracing backwards through the eye as an optical system. For example, in an emmetrope, the far point is at optical infinity. This is found by taking the inverse of plano power, zero, or by tracing a point on the retina backwards through the emmetropic eye to find that it emerges as parallel light, see Figure 1a.
Figure 1. Far points in refractive error
The far point of refractive error is defined as the distance at which an object can be seen clearly by an eye that is not accommodating. It is found mathematically or by tracing light backwards through the eye. a. Light traced backwards through an emmetropic eye emerges as parallel rays, creating a far point at optical infinity. b. In a hyperopic eye, light emerges as diverging rays to create a far point behind the retina. c-d. The far point of a myopic eye is found between the retina and optical infinity since converging light exits the eye. Higher degrees of myopia produce stronger convergence of light and a far point closer to the front of the eye.
Parallel light focuses behind the retina in a hyperopic eye, so converging light must enter the eye for a focused retinal image. Subsequently, the far point of a hyperopic eye is found behind the eye, as this point must contribute some convergence of light to form a conjugate point on the retina.[4] Its location is often deemed ‘beyond infinity,’[5] see Figure 1b.
In a myopic eye, incoming parallel light focuses in front of the retina; diverging light must enter the eye for an image to be in focus. Therefore, the far point of a myopic eye is between optical infinity and the front of the eye. The higher the magnitude of myopia, the closer the far point to the front of the eye, see Figure 1c-d.[4]
Optical Principles of Retinoscopy
Retinoscopy is based on reflection of light after it has passed through the refracting surfaces of the eye.[1] The direction, speed, and brightness of the reflected light are dependent on the refractive error present within the eye.
The far point of an eye ultimately determines the reflection, or motion, of light that is seen during retinoscopy. The far point signifies where light from the retinoscope focuses after refracting through the eye. This focus point acts as a fulcrum for the direction of light.
If the far point is located behind the retinoscope, light focuses behind the observer. This point of focus becomes a fulcrum, so there will be no change in the direction of light observed since it is located behind the clinician. Therefore, as the light from the retinoscope moves down, so does the reflected light, e.g. ‘with’ motion is observed. Similarly, a far point located behind the patient’s retina will create a fulcrum beyond the eye’s optical system, creating no change in the direction of light; with motion will be observed, see Figure 2a-c.
Figure 2. With motion retinoscopy reflex. a. Light that comes to focus behind the retinoscope acts as a fulcrum for the retinoscopy reflex, so the beam and the reflex move in the same direction. b. Similarly, light focused behind the patient’s eye puts the fulcrum behind the reflex, so the beam and observed reflex move in the same direction. c. A schematic of with motion from the observer’s perspective. The retinoscope beam (yellow) moves in the same direction of the reflex (orange) within the pupil.
In refractive errors where the far point is located between the retinoscope and the patient’s eye, light comes to a focus point before reaching the doctor’s eye. This point acts as the fulcrum, so as the light from the retinoscope moves down, the reflected light moves up, e.g. ‘against’ motion is observed, see Figure 3a-b.
Figure 3. Against motion retinoscopy reflex. a. Light coming to focus between the eye and the retinoscope acts as a fulcrum for the retinoscopy reflex. b. A schematic of against motion from the observer’s perspective. The retinoscope beam (yellow) moves in the opposite direction of the reflex (orange) within the pupil.
In the cases where the far point is located in the plane of the retinoscope, no motion, e.g. ‘neutral’ motion, is observed. When the reflected light focuses at the retinoscope, the observer is at the fulcrum, so neither ‘against’ nor ‘with’ motion is seen, see Figure 4a-b.
Figure 4. Neutral motion retinoscopy reflex. a. If light comes to focus at the plane of the retinoscope, the observer is at the fulcrum for the retinoscopy reflex. b. A schematic of neutral motion from the observer’s perspective. As the retinoscope beam (yellow) moves across the pupil, the reflex (orange) creates a bright, even flash within the pupil.
By combining knowledge of refractive error, far point, and retinoscopy reflex, a pattern can be seen.
‘Against’ motion is observed during retinoscopy with myopia greater than the inverse of the retinoscope distance. ‘Neutral’ motion is seen when the amount of myopia is equal to the inverse of the retinoscope distance. ‘With’ motion is observed for hyperopia, emmetropia, and myopia less than the inverse of the retinoscope distance.
In all cases, the goal of retinoscopy is to achieve ‘neutral’ motion by changing the accessory lenses in front of the eye.[2] After neutrality is achieved, the doctor must compensate for the retinoscope distance to find the true refractive error of the eye, see Retinoscopy Technique: A Step-by-Step Approach.
The Retinoscope
Setting Up for Retinoscopy
It is important that the patient’s accommodation is relaxed throughout retinoscopy, as accommodation can affect the far point of the eye and lead to incorrect determination of refractive error. Therefore, a large distance target should be used. A 20/400 letter is often used for adults, teens, and very cooperative children, while a video clip or movie on a distant screen is usually more useful for younger and less cooperative patients.[6]
Even with a proper distance target, it can be difficult to ensure relaxed accommodation in younger patients. Most practitioners perform a second retinoscopy reading on children after dilation with tropicamide or cyclopentolate to determine refractive error;1 this is especially important in cases where high hyperopia or pseudomyopia is suspected.
Next, the retinoscope distance, e.g. working distance of the practitioner, must be determined so it can be accounted for in the retinoscopy results.6 The most common working distance is 67cm; this is approximately arm’s length for most practitioners. For shorter practitioners, a working distance of 50cm may be more comfortable.
To determine the working distance, the retinoscope should be held in the dominant hand in front of the doctor’s eye with the body turned approximately perpendicular to the phoropter and the non-dominant hand outstretched toward the sphere wheel of the phoropter. The distance between the retinoscope and phoropter is measured in this position; this is the working distance. It may be a good idea to measure this distance the first few times retinoscopy is performed to ensure a standard working distance.
he inverse of the working distance in meters gives the working distance in diopters. This should be dialed into the phoropter before beginning retinoscopy to account for the light from the retinoscope being closer to the patient than the distance target. The working distance can either be dialed in using the sphere wheel or the “R” lens in the phoropter (note: the “R” lens is a +1.50 lens, so the practitioner may need to adjust working distance accordingly). The working distance will be removed when the retinoscopy procedure is complete, see Table 1.
Working distance correction to retinoscopy results varies per practitioner based on the preferred distance between the practitioner and the phoropter. Common distances and the corresponding corrections are shown in the table.
Retinoscopy Technique: A Step-by-Step Approach
1: Make sure only the working distance compensation is dialed into the phoropter. The retinoscope should be in plano mode with the sleeve down.[2]
2: The patient should be instructed to fixate on an appropriate distance target. Both eye wells should be open.
3: While standing approximately 15 degrees temporal to the patient’s line of site in the right eye,[2] the doctor should aim the streak of retinoscope light into the patient’s right eye. Gently sweep the beam back and forth across the pupil to determine the light reflex. Keep in mind, the reflex observed describes the power of the eye in the meridian perpendicular to the light beam.[6]
4: Continue gently sweeping the light beam across the pupil while slowly rotating the beam 360 degrees. If the reflex is constant throughout, the patient has a spherical refractive error. If the reflex changes, astigmatism is likely present.[6] Note: many practitioners will begin by scoping only the 180 and 090 meridians since the majority of astigmatic patients require cylinder correction in those meridians.[2]
5: If working with a plus cylinder phoropter, find the most minus/least plus meridian first. The most minus/least plus meridian will have either the slowest, dullest ‘with’ motion or the fastest, brightest ‘against’ motion when compared with the other meridian.
6: Neutralize the most minus/least plus meridian if astigmatism is present. If ‘with’ motion is observed, add plus lenses until ‘neutral’ is achieved; if ‘against’ motion is observed, add minus lenses until ‘neutral’ is achieved. The reflex is ‘neutral’ when the retinoscope reflex “blinks red” across the pupil.[2]
a: Helpful hint: the speed and brightness of the beam indicate the proximity to neutrality. When nearing a neutral reflex, the reflex beam will appear to move faster and become brighter.
b: Another helpful hint: to remember which lens to add with a given type of motion, remember SPAM. For Same (‘with’) motion, add Plus; for ‘Against’ motion, add Minus.[6] Another memory trick is against motion, add minus.[2]
7: Turn the retinoscope beam 90 degrees; ‘with’ motion should be observed if astigmatism is present. Align the cylinder axis with the retinoscope beam and add plus cylinder until ‘neutral’ motion is seen. Remember, the orientation of the retinoscope beam is perpendicular to the meridian being scoped, just as the axis of the lens prescription is perpendicular to the meridian that needs the astigmatic correction.[2]
8: Repeat steps 3-7 for the left eye.
9: Recheck the right eye. Accommodation may change slightly as the second eye is neutralized which can affect the end measure for the first eye scoped.
10: Remove the working distance from the phoropter. This can be achieved by changing the retinoscope lens back to open well or by walking back the sphere lens dialed in during setup.[6]
11: Check monocular visual acuities.[2] If the monocular visual acuity is worse than 20/40, consider repeating retinoscopy.
Troubleshooting
The following are examples of problems that may arise during retinoscopy and the best way to solve them.
Minus cylinder phoropters are being utilized in place of plus cylinder phoropters.
There is no change to the setup and steps 1-4. At step [5], neutralize the most plus/least minus meridian first. This will be the meridian with the slowest, dullest ‘against’ motion or with the fastest, brightest ‘with’ motion. After neutralizing the sphere meridian and turning the retinoscope beam 90 degrees, ‘against’ motion will be observed. All remaining steps are the same as for plus cylinder phoropters.
After neutralizing the sphere meridian and turning the retinoscope beam, ‘against’ motion is observed instead of ‘with’ motion in a plus cylinder phoropter.
No problem! The wrong meridian was neutralized first, but this is easy to solve. Simply add minus lenses in the ‘against’ motion meridian until neutrality is observed. Then spin the beam back to the initial meridian; ‘with’ motion should be seen. Cylinder lenses are added until neutral motion is noted.
The patient looks at the retinoscope beam instead of the distance target.
If patient fixation is consistent on the light from the retinoscope, the test becomes a type of near retinoscopy. To find a distance measurement in this case, do not remove the working distance from the final prescription.
The patient has a short attention span/limited fixation.
Practice getting faster at retinoscopy. Consider using sciascopy bars or loose lenses for neutralization, as they often give quicker feedback. Be careful to keep track of which meridian is being neutralized when using sciascopy bars or loose lenses; it may be helpful to draw the powers on an optical cross and then convert it to a lens prescription. Remember, the meridian being neutralized is the meridian perpendicular to the beam of light from the retinoscope.
No reflex is seen through the phoropter wells.
This can be a myriad of situations. This is often observed with high refractive error; consider turning the small sphere wheel for +/- 3.00D jumps in power to see if a reflex can be observed through stronger lenses. The retinoscopy reflex may be extremely dull with moderate to severe cataracts or significant corneal disease. Move closer to see if a reflex can be seen with a stronger light stimulus. A reflex may also be difficult to discern with miotic pupils. Moving closer or dilating the patient should help in this case.
The reflex seems to fluctuate between with and against while scoping along a single meridian.
It is most likely that the patient’s accommodation is not relaxed. First, ensure the patient is looking at a large distance target. If the reflex continues to fluctuate, the patient is likely a hyperope with some degree of latent hyperopia. Repeat retinoscopy after dilation with tropicamide or cyclopentolate.
The reflex is irregular or looks abnormal.
This is often a sign of ocular disease. A black spot in the middle of the reflex may be a sign of posterior subcapsular cataracts, while spokes at the edges of the reflex can be a sign of cortical cataracts. A scissoring reflex is one of the most common signs of keratoconus. In this scenario, one half of the reflected retinoscope beam will show a simple ‘with’ or ‘against’ motion; the other half of the reflected beam is split into two separate beams that scissor, or clap, against one another as the retinoscope beam sweeps across the pupil.
The cylinder axis appears to shift or rotate as cylinder correction is added.
This can happen if the patient’s accommodation is not fully relaxed. Ensure the patient is looking at a large distance target. A rotating axis can also be observed with high amounts of astigmatism. Continue adding cylinder correction at the original axis until neutral is observed. Recheck both meridians before moving to the other eye and adjust the axis if needed.
References
1. Retinoscopy. American Academy of Pediatric Ophthalmology and Strabismus.
https://aapos.org/glossary/retinoscopy. Published January 2020. Accessed August 24, 2020.
2. Krueger J. Step Up Your Retinoscopy Skills. OptometryStudents.com.
https://www.optometrystudents.com/pearl/retinoscopy/. Published June 13, 2017. Accessed August 24, 2020.
3. VanArsdale E. A Beginner’s Guide to Conducting a Retinoscopy Procedure. Keeler.
https://blog.keelerusa.com/retinoscopy/. Published August 31, 2017. Accessed August 24, 2020.
4. The Far Point and Refractive Error. American Academy of Optometry.
https://www.aao.org/Assets/8e7ff7d8-de38-412a-8165-
6c5f7b11e432/637151349567070000/bo5-pdf?inline=1. Accessed August 24, 2020.
5. Thakur R. Retinoscopy and its principles. Slideshare.
https://www.slideshare.net/laxmieyeinstitute/retinoscopy-and-its-principles. Published June 23, 2014. Accessed August 24, 2020.
6. Lee O. Retinoscopy 101. American Academy of Ophthalmology: Young Ophthalmologists. https://www.aao.org/young-ophthalmologists/yo-info/article/retinoscopy-101. Published May 16, 2015. Accessed August 24, 2020.
Identifier: Moran_CORE_126056
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