Don’t Be Shortsided

A low myope walks into an optometry clinic…

To many, this may sound like the beginning of a successful patient encounter. Correct myopia with a distance prescription; you’ll have a happy patient and a happy practice. In my clinic, however, myopia is never trusted. In fact, this encounter raises alarm for a different, insidious condition masquerading as myopia; pseudomyopia.

Pseudomyopia refers to a temporary shift in refractive error due to overstimulation of the eye’s accommodative system. Both myopia and pseudomyopia share a similar symptom of blur, but pseudomyopia may cause frontal headaches and eyestrain as well. It is important to differentiate between the two conditions because treatment for each is substantially different. While fully correcting myopia is beneficial to a patient, prescribing minus lenses for a patient with pseudomyopia may further stimulate the process and exacerbate symptoms.

So, how do we avoid this trap? Don’t be short-sighted. Before prescribing, look outside the phoropter and evaluate your patient’s lifestyle. Identify which functional adaptations could have led to this refractive error such as close working distance or work-place ergonomics. Then, consider what your prescription can do for their visual success in the future. Giving a patient what they want isn’t necessarily equivalent to what they need. Here are some tips to help you navigate an exam for a pseudomyopia suspect.

1. Investigate the chief complaint

Just like every red eye is not a bacterial conjunctivitis, every blurry eye is not myopic. When a patient reports blurry vision we need to dig a little deeper. Ask the following questions to get a thorough understanding of the compliant.

1. Frequency: How often does the blurry vision occur? Does it occur more at the end of the day?
2. Consistency: Is the blur constant or intermittent?
3. Associated symptoms: Do your eyes feel sore? Do you get headaches?
4. Associated activities: Are the symptoms worse after reading or doing computer work?

Blur can be constant or intermittent for patients with pseudomyopia. However, it occurs more frequently after prolonged near work. If a patient reports headaches, ask about the location of the headaches. Patients with headaches secondary to visual stress will often complain of frontal or tension headaches. These headaches also occur more during school hours or at the end of a long workday. If the symptom of distance blur presents in a child, don’t forget to ask the parent about reading habits. Avoidance of reading qualifies as a symptom. If an activity creates stress we tend to avoid it unless that stress is eliminated. Pseudomyopia can often be a consequence of accommodative stress. Since vision is part of a continuum, performance at near can affect the quality of vision at distance.

2. Perform an objective refraction

A retinoscope can tell you about the quality and stability of the visual reflex which plays an important role in your diagnosis. The autorefractor will not be able to pick up a fluctuating reflex in an undilated eye. In fact, it may lead you down a rabbit hole by showing significant myopic prescription. Free space retinoscopy is preferred to phoropter retinoscopy because the phoropter may simulate an enclosed environment stimulating accommodation. Theoretically, a large distance target should control accommodation however, patients with pseudomyopia tend to over-accommodate at all distances so you need to eliminate all confounding variables.

During retinoscopy, take a few moments to look at the stability of the reflex. If it fluctuates, you should suspect accommodative dysfunction unless proven otherwise. Sometimes it may be difficult to get a good estimate of the prescription due to this fluctuation. If this is the case, fog the patient binocularly with lenses equivalent to your working distance to minimize the fluctuation. While cycloplegia is the best method to control accommodation, fogging may help you get a better starting point and avoid the extra minus during refraction. In patients with accommodative dysfunction, assess visual acuities binocularly prior to monocular acuity. Monocular acuities may be worse due to enhanced accommodation. If visual acuities are significantly disproportional to your objective prescription then probe further into the function of the accommodative and binocular system.

Testing

1. Use a large distance Snellen target. A video may also be used to engage younger patients.
2. Perform retinoscopy in free space with loose lenses or retinoscope bars.
3. Assess the quality and stability of the reflex while neutralizing it.
4. Use the fogging technique in a patient with a fluctuating reflex. Fog the patient with the lens equivalent to your working distance. For example, if your working distance is 50cm, fog binocularly with a +2.00D lens.   

3. Check accommodative status

There are multiple ways to measure accommodation and each method will tell you something different about function. Minus lens amplitudes tell you about the amount of accommodation, monocular estimate method (MEM) tells you about accommodative accuracy and clearing plus/minus flippers reveals accommodative flexibility. Patients with pseudomyopia tend to have an inaccurate accommodative response to targets which is responsible for blur. Therefore, testing accommodation can help solidify your diagnosis.

Accommodative amplitudes can be normal or reduced in patients with pseudomyopia. The rigidity of the ciliary muscle causes the plane of focus to be in front of the plane of the target thereby accounting for the blur and low amplitudes. To that effect, MEM will likely show a lead of accommodation characterized by a hypertonic response to a near target (neutrality with +0.25D lens or lower/minus lenses). In a normal system accommodative accuracy shows a lag of +0.50D to +0.75D. In addition, accommodative flexibility may be reduced as demonstrated by the inability to clear age-appropriate plus lenses.

Testing

1. Amplitudes: Use the best estimate of an objective distance prescription. Within the phoropter, monocularly increase the power of minus lenses as the patient views a near target which is 2 lines above their best corrected near visual acuity. This method is preferred over push up amplitudes for consistency in results and eliminating the confounding variable of target size. Use a near point card and measure first sustained blur for each eye.
2. Accuracy: Use any target which is 2 lines above best corrected near visual acuity. If you don’t have MEM cards, simply use a near card with words or numbers which stimulate an accommodative response. Dim the lights, pick up your retinoscope and insert low powered plus lenses in front of each eye as the patient reads the card 16 inches away. This is a binocular technique. Lenses should be inserted momentarily over one eye at a time to prevent adaptation. If you are worried about holding your retinoscope, a loose lens and the near card at the same time, don’t be. Your dexterity will shock you.
3. Flexibility: This technique can be time-consuming in a primary care exam because it is meant to be performed for 1 minute each eye, monocularly. Therefore if you are crunched for time, perform the first two techniques. For pediatric patients under 13 years old use a +/-2.00 flipper and for adults use a +/-1.50 flipper. If a patient has reduced amplitudes, the power of flippers may need to be modified for this test. Binocular flippers introduce vergence, therefore, we will defer that technique for now. There are multiple normative values for the monocular test based upon the study you reference. For the purposes of this article, the normative data we will use is 10 cycles per minute/per eye.

4. Check binocularity

Accommodation and convergence are linked neurologically. Because of this, if a patient has accommodative dysfunction often times it is accompanied by poor binocularity. One of the best screening tests to check binocularity is stereopsis. In order to have good depth perception you need to have good binocular function. Wirt circles are a good method of assessment. Sure, there are monocular cues which can aid a patient, however since we are using this as a screening test, it is still helpful in identifying major binocular problems.

Interestingly over-accommodation can be a result of convergence insufficiency or convergence excess. A patient with poor convergence may use their accommodative system to stimulate binocular function and hence end up over-accommodating. Performing a near point of convergence test (NPC) with and without an accommodative target can help you identify an underlying binocularity issue. If NPC significantly worsens with a non-accommodative target such as a penlight then the patient likely has a convergence problem. In contrast, a patient’s over-stimulated accommodative system could lead to convergence excess. Cover test may show esophoria at distance and near. Additionally, compensating base-in ranges and recovery on base-out ranges can be reduced.  In either case, whether it’s over or under convergence, the dysfunction needs to be corrected in combination with accommodation.

Testing

1. Stereo: Patients should be fully corrected. Minimize monocular cues by maintaining a stable working distance of 16 inches and holding the stereo book flat against a desk. Additionally, keep the patient from manipulating and tilting the book to prevent influence from monocular cues.

2. Cover test: Perform at 20 feet and 16 inches using a target 2 lines above best-corrected visual acuity. Recall that patients with pseudomyopia complain of distance blur so you may need to use a target bigger than 20/40 depending on their best-corrected binocular visual acuity.

3. Near Point of convergence: Check convergence with a penlight to isolate the vergence system from the accommodative system. This method will give insight into gross convergence issues. Start from 16 inches and slowly move the penlight closer until diplopia is reported or suppression of one eye is observed. If this test is performed too quickly, convergence issues could go undiagnosed. Make sure to also test recovery. Once convergence has broken down, at what point can the patient recover single vision. This tells you about control over the binocular system.

5. Cycloplege: Tropicamide vs. Cyclopentolate

A true confirmation of pseudomyopia can only be determined status post cycloplegia. So, if all the previous testing leads you to suspect over-accommodation, take the time to cycloplege the patient. Sending them home with a minus prescription may temporarily solve their problems and seem like an easy fix, but it will not address the underlying issue.

The two cycloplegic drops used most commonly in a clinical setting are Cyclopentolate (1%) and Tropicamide (1%). While Atropine holds the gold standard for cycloplegia, it is not practical to use clinically due to the delayed onset, side effects and long recovery time. Numerous studies have been done to compare the efficacy of cyclopentolate vs. tropicamide in controlling accommodation. A meta-analysis in 2018 reported that although cyclopentolate produces a “stronger” cycloplegic effect, it is not clinically significant when assessing distance refractive error. The peak time of onset to produce cycloplegia is 20-30 mins for tropicamide and 45 minutes for cyclopentolate which makes the use of tropicamide efficient. Residual accommodation, when measured with objective measures also demonstrated minimal difference between cyclopentolate vs. tropicamide. Additionally, tropicamide is more readily available in all types of clinical settings than cyclopentolate. Cyclopentolate remains to be the preferred drop of choice statistically for children with high hyperopia or straismbus, however, tropicamide is a suitable clinical alternative.

For the purposes of pseudomyopia, cycloplegic refraction after administering tropicamide can provide sufficient insight into the true nature of the condition. Since you plan to dilate the patient for ocular health assessment anyways, it is advised to wait a few extra minutes to achieve a cycloplegic effect. Agreeably, it is not practical to cycloplege every myopic patient that walks into your clinic so stay alert for the patients at risk. These include low myopes, moderate myopes who have a substantial refractive error shift within 6 months, and hyperopes with asthenopia complaints.

Testing

1. Administer 1 drop of tropicamide into each eye.
2. Wait for 20-30 minutes after the last drop has been administered to achieve maximum cycloplegic effect.
3. Perform retinoscopy in free space.
4. Re-measure distance visual acuity with your objective prescription.

6. Prescribing considerations

Now that you’ve made the diagnosis of pseudomyopia it is important to educate the patient about the condition and treatment options. The habitual cycle of near point stress leading to accommodative dysfunction needs to be broken to achieve desirable results. This can be achieved by combining the following three steps.

1. Visual hygiene: The ideal working distance is known as the Harmon distance. To measure, place a closed fist against the chin and measure the distance from fist to elbow. Working at a closer distance than this can cause accommodative stress which leads to improper visual adaptations. Inform the patient about the 20/20/20 rule designed by Jeffrey Anshel, OD. Every 20 minutes, take a twenty second break and look 20 feet away. The distance of 20 feet can be difficult to judge so try looking out a window at a distant object. These breaks are doctor recommended.
2. Low plus reading glasses: Rather than a minus lens which can stimulate the accommodative system, patients with pseudomyopia benefit from a low plus lens to relax the ciliary tone while performing near tasks. The reason why a low plus lens is advised over a higher-powered lens is because patients with accommodative excess may have difficulty clearing a significant amount of plus due to the rigidity of the ciliary muscle. A low powered lens will help relieve some of the accommodative effort without blurring the patient. To determine what power of plus the patient needs use your cycloplegic prescription and MEM as aids. If the patient is a hyperope post cycloplegia and had a spasm on MEM evaluation, prescribe the amount of hyperopia for reading. In clinical practice, the lowest amount of plus I prescribe for these cases is +0.75. This is because we need to push plus to reboot the accommodative system and +0.75D is a good starting point.
3. Vision Therapy: In my opinion glasses alone only relieve some of the accommodative effort, but in order to break the pattern of over-accommodating the brain needs to be re-wired. Vision therapy changes the message from the brain to the muscles by repetitive input, which strengthens neural connections. Exercises target the accommodative and binocular system to achieve a balance between them at all distances. The patient is trained to use an appropriate working distance for all exercises which translates into its application in the real world. A combination of glasses and vision therapy help remediate the underlying visual dysfunction and prevent readaptation in the future.

While every myopic patient may not have pseudomyopia, before prescribing minus lenses take some time to investigate the root of the refractive error. As optometrists, our bread and butter is earned providing a good prescription for the patient so consider what your prescription can do for the patient long term. The steps listed above take minimal additional time to your exam sequence and may save you a glasses re-do. Alternative treatments for severe pseudomyopia secondary to a significant accommodative spasm have been reported in the literature. These involve a combination of weekend cycloplegic drops and reading glasses. The treatment presented in this article is for mild to moderate pseudomyopia. Even if your practice does not have vision therapy, the correct diagnosis and a reading prescription is a vital start to the treatment process. Further than that, you can always refer to a colleague for co-management.

Suggested reading

https://www.ncbi.nlm.nih.gov/pubmed/8115124

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6039578/

https://iovs.arvojournals.org/article.aspx?articleid=2199995

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2907036/