What is pseudomyopia? Avoiding overcorrection in children

What is pseudomyopia and how often does it occur? How can we avoid overcorrection in young myopes? Myopia has been defined as when the refractive state is equal to, or more minus, than -0.50D when ocular accommodation is relaxed.¹ But transient myopia, which can also be called accommodative spasm or pseudomyopia, occurs when the accommodative system is not relaxed, making a patient falsely seem to need more minus lens correction power.

This issue may be quite common in our young population: the Anyang Childhood Eye Study surveyed a variety of factors in over 4500 school-aged children. Pseudomyopia was defined as exhibiting myopia of at least −0.50D before cycloplegia and less than −0.50D after cycloplegia: being emmetropic on cycloplegic refraction. Subtracting the two gave the amount of pseudomyopia, and measures were taken by autorefraction.²

The younger children showed mean pseudomyopia of 1.13D and for older children it was 0.38D. Among these children, 1 in 6 were wearing spectacles - which they obviously didn't need. There was not enough statistical power to test if wearing unneeded glasses sped up eventual myopia progression.

There was no link found between pseudomyopia and time spent on near work or time spent outdoors. After one year, 16% of these 6-year-olds and 11% of the 13-year-olds had become myopic, but this progression was not any faster than in the true myopes.

Concerningly, this study found that 50% of the younger children and 13% of the older children wearing spectacles for myopia were overcorrected by at least 0.50D. Only around one-third were wearing an accurate correction in spectacles, while 10% of the younger and 50% of the older children were undercorrected.

The Anyang Childhood Eye Study surveyed '127 optical stores' and reported that 72% did not use any methods to relax accommodation during refraction. Around one-quarter used fogging methods and only 3% routinely used cycloplegia for a myopic child's first refraction.

Retinoscopy with fogging is an ideal refraction technique as it allows for both an accurate refraction and evaluation of the subsequent binocular vision response. Retinoscopy is the best screening tool for detecting amblyogenic risk and detecting refraction when done by an optometrist or ophthalmologist^3,4 and is listed in the Optometry Australia's paediatric eye care reference guide as the primary refraction technique for children up to age 7, and in the American Optometric Association's Clinical Practice Guideline on Pediatric Eye and Vision Examination as the preferred technique for school aged children. The American Academy of Ophthalmology Pediatric Preferred Practice Guideline on Pediatric Eye Evaluations agrees, stating that "Patients should undergo cycloplegic refraction to determine refraction with retinoscopy, followed by subjective refinement when possible."

Fogging the non-tested eye during retinoscopy yields results within 0.3D of cycloplegic outcomes in children.⁵ The amount of fogging doesn't seem to influence the result, with anywhere from +1D to +5D yielding similar results.⁶

For children, ensuring enough plus to relax accommodation is key. Considering that the +2.00 'fogging test' is successful in detecting hyperopia in children 5-11 years,7 this seems a reasonable amount for fogging in childhood retinoscopy.

Read An Ode to My Retinoscope for many more ways retinoscopy can help from childhood refractions to keratoconus screening to contact lens practice.

A cycloplegic refraction is the hallmark of refractive accuracy and the gold standard for research studies; but the IMI Clinical Management Guidelines⁸ don't necessitate cycloplegic refraction at each examination of a myopic child. Rather they suggest using cycloplegia when indicated, which may vary depending on the practitioner, country, availability and the presentation of the patient. If used, the recommended dosage for cycloplegic refraction is two drops of 1% cyclopentolate or tropicamide given 5 minutes apart. Cycloplegic refraction should be performed 30 to 45 minutes after the first drop is instilled. Read more about this, including clinical presentations where cycloplegia is necessary, in How to Achieve Accurate Refractions for Children.

1. Check presenting acuity against the refractive change. Be suspicious where the unaided and/or acuity measured with the child's current correction doesn't match the change found on refraction. One line of letters should equate to around 0.25D. In children, an acuity cutoff of 6/9.5 or 20/32 has a high specificity and sensitivity for detection of at least -1.00D of myopia.⁹
2. Try the monocular +1.00 blur check. Measure the new best-corrected monocular acuity, then add +1.00 to one eye with the other eye occluded. The patient should blur to around 6/9 to 6/12 (20/30 to 20/40). If this doesn't occur, keep adding more plus until the patient's acuity blurs to the expected level. Then reduce the power in 0.25D steps, encouraging your patient to keep reading smaller lines and 'earning the extra minus' until there is no further improvement in vision.¹⁰ Some children may be less tolerant of blur and deteriorate from normal acuity to less than 6/12 or 20/40 with the monocular +1.00 - this is just variation and doesn't mean more minus is needed.
3. Consider the correlation to axial length. While not a perfect correlation, 0.4mm of axial progression equates to around 1.00D.¹¹ To avoid overcorrection, be suspicious if axial length shows only a minimal change, out of step with a larger refractive change.
4. Binocular balancing techniques. Requiring equal acuity in both eyes, the techniques of alternate occlusion, prism dissociated blur balance, prism dissociated duochrome or Humphriss Immediate Contrast method all show similar accuracy.¹² Watch Dr Kate Gifford explain an adapted alternate occlusion technique here.

• How to achieve accurate refractions for children

• Case study: Refraction challenges in children - what to prescribe?

• Case study: A myope or not? Pseudomyopia, antimetropia and more.

• Case study: What happens to binocular vision during cycloplegia?

Check out Myopia Profile's two hour, intensely practical online course Mastering Refraction for Kids. Upskill with interactive text, downloads, animation and video demonstrations, prescribing advice, test-your-knowledge challenges and more. This course will increase your knowledge, clinical skills and confidence in refraction techniques and prescribing decisions for children of all ages and refractions - not just myopes! Click the link to learn more and try the first few lessons for free.