Author : Dylan Vella, Orthoptist
Contact : info@threedom.it
Background
Anisometropic amblyopia typically necessitates appropriate refractive correction, with occlusion therapy recommended only if deemed necessary.
It is well-established that certain forms of amblyopia can be resistant to treatment, occasionally due to idiopathic factors or due to the age.
Accommodation lag in amblyopia is a delay or deficiency in the eye's ability to focus accurately on near objects, often resulting in blurred vision, as the amblyopic eye struggles to maintain the required accommodative response.
This case report offers valuable insights into a potential cause for treatment resistance and illustrates a successful implementation of amblyopia therapy in patients who may experiencing unilateral accommodation lag.
Case presentation
This case report describes a 9-year-old boy with amblyopia secondary to anisometropia with unilateral accommodation lag, leading to visual impairment. Notably, there was no evidence of damage to the visual pathways.
Conclusions
This case report highlights the importance of assessing accommodation in both monocular and binocular conditions.
It emphasizes that when amblyopia is associated with unilateral accommodation lag, an additional lens may be applied to the amblyopic eye during therapy.
Keywords
binocular vision, refractive error, pediatric refraction, spectacle correction, visual rehabilitation
Declaration of interest
The author reports no conflict of interest.
Acknowledgments
I would like to express my heartfelt gratitude to a dear colleague who provided invaluable support during the writing process with his feedbacks. Thank you, Gianni!
Introduction
Amblyopia(1) is the leading cause of monocular visual impairment in children and young adults, occurring in about 1% to 3.5% of the population in developed countries.
This visual disorder can often be reversed if identified and treated early.
Amblyopia is caused by any condition that creates a difference in vision between the two eyes.
The most common causes leading to this disparity include refractive errors (the need for glasses), strabismus (ocular misalignment), other conditions that block the visual axis, or a combination of these factors.
Strabismic and refractive causes account for 90% of all amblyopia cases.
In cases where there is residual visual disparity after achieving the best possible visual acuity with glasses, treatment options for remaining amblyopia include patching the fellow eye or using atropine to penalize it.
These treatment options have advantages and disadvantages.
Patching requires complete occlusion of one eye.
The most common method is using disposable adhesive patches, though reusable patches mounted on glasses are also available.
The prescribed duration for patching can range from one hour to all day.
Atropine works by impairing the focusing ability of the eye, which reduces near visual acuity for all patients and can affect distance vision in some cases, lasting for several days.
A minimum level of accommodative accuracy is necessary to ensure that a clear image of a near object is projected onto the retina(2).
When an eye does not accommodate enough, known as accommodative lag, or accommodates too much, referred to as accommodative lead, it can exceed the normal physiological depth of focus (typically ± 0.5D).
This results in noticeable near blur due to hyperopic defocus, which may negatively affect visual acuity.
Research has consistently shown that amblyopic eyes exhibit a greater lag in accommodation.
This lag tends to be more pronounced in monocular viewing conditions compared to binocular ones.
While the precise cause of this phenomenon is not fully understood, it is likely linked to early and prolonged abnormal visual experiences within the sensory visual system.
Whether treatment for amblyopia leads to improvements in accommodative function remains uncertain.
Some studies have reported enhancements in accommodative function post-treatment(3), while others have found results to be inconsistent(2) on an individual basis, with the reasons for this inconsistency still unclear.
The article aims to investigate a potential cause of treatment resistance in anisometropic amblyopia associated with monocular accommodation lag.
It highlights the need for comprehensive accommodation assessments, especially in cases non-responsive to standard occlusion therapy.
Presenting a case where accommodative deficiency may have limited visual improvement, it explores the tentative role of corrective lenses in addressing accommodation lag, offering insights into possible strategies for enhancing visual rehabilitation in pediatric patients.
How to assess the accommodation in young children?
In young children, the author believes it is neither feasible nor essential to measure accommodative amplitudes, as effective assessment methods are lacking.
The push-up method, proposed by Donder, is not suitable because it relies on psychophysical principles, which are problematic when working with children; their responses can be unreliable. Additionally, two studies indicate that even older children do not find this method effective(4,5).
The assessment of accommodation should not be conducted only binocularly, especially when trying to exclude a monocular accommodative lag associated with amblyopia.
This is because the accommodative reflex, like the pupillary reflex, is always binocular and symmetrical.
Let’s consider an experiment to completely dissociate the eyes in a patient with normal accommodative ability and emmetropia.
We have the right eye fixate on a target placed at least 3 meters away, while the left eye fixates on a target at 40 centimeters.
We will then assess the accommodative reflex using dynamic retinoscopy in both eyes—first when the subject is fixating with the right eye, and then with the left.
We will observe that when the subject fixates with the right eye, the accommodative reflex does not occur in either eye. However, when fixating with the left eye, the accommodative reflex is present in both eyes, despite the right eye not receiving any accommodative stimulus.
Now, considering a patient with monocular accommodative lag, the conclusion is clear.
For this reason, the author believes that even this sophisticated and interesting tool (Grand Seiko autorefractor(6)) requires some adjustments, and its effectiveness should be verified even under monocular conditions.
According to the author, currently the dynamic retinoscopy(7) is the most effective method for assessing accommodation in children aged 6 months to 14 years.
Dynamic retinoscopy should be performed both monocularly and binocularly.
The author always performs dynamic retinoscopy on every patient.
A streak retinoscope and Lang's fixation cube are the necessary materials.
For screening purposes, it is sufficient for the patient to look at an index finger or any finger of the hand as fixation’s target. This test will be conducted monocularly, especially in the presence of amblyopia or anisometropia.
Case presentation
A 9-year-old child is being examined by the author for the first time.
He has been wearing glasses for at least six years and has been attending check-ups with an orthoptist every three months since he started using them, with an ophthalmologist once per year.
A treatment plan for the right eye has been recommended, involving part-time occlusion for 1-2 hours each day.
His current prescription is as follows:
OD +4.25; -1.00 / 180
OS +6.50; -2.25 / 175
The last objective refraction in cycloplegia was recorded in December 2023 as :
OD +5.25; -1.00 / 175
OS +7.25; -2.25 / 180
The orthoptic evaluation shows amblyopia in the left eye, with distance vision of 1.0 in the right eye and 0.60 in the left eye.
Near vision is 1.0 in the right eye and 0.3 in the left eye.
There is no manifest strabismus, only slight exophoria for near vision.
The Lang-Test I showed a positive result of 3/3.
There is a slight physiological anisocoria, with the left pupil being slightly larger than the right one, maintaining the same proportion in both photopic and scotopic environments; the difference is less than one millimeter.
Monocular accommodation assessed through dynamic retinoscopy is normal in the right eye but absent or reduced in the left eye.
Binocular accommodation is symmetrical and normal in both eyes.
The vision in the left eye does not improve quantitatively for near vision with a +3D lens, but qualitatively it improves, as the patient reports seeing better with the lens.
Therefore, I have recommended occlusion therapy for 4-5 hours per day and advised that, when possible, an additional +3D lens be worn over the lens of the amblyopic eye during near activities for at least 1-2 hours per day.
At the three-month follow-up, the child reported difficulty tolerating the additional lens but confirmed completing occlusion therapy for 3-4 hours daily. During the examination, accommodative response was within normal limits, both binocularly and monocularly in each eye.
Visual acuity showed an improvement of 0.1 for both distance and near.
Results
The +3D additional lens was likely too strong and not well-tolerated; a +2D lens might have been a more suitable choice.
However, it’s possible that simply attempting this lens or focusing more attention on the issue contributed to some improvement in visual acuity.
For unclear reasons, accommodative function is now within normal limits.
Could the accommodation lag simply reflect, rather than cause, amblyopia?
Because of amblyopia, the eye has a visual deficit that limits stimulation needed for proper accommodation.
When the image is too blurred, the brain may lack the neural impulse necessary to drive accommodation effectively.
In this case, the improvement in vision due to occlusion therapy might allow the eye to start accommodating properly.
Given the somewhat unpredictable progression of this case, I remain uncertain about the diagnosis of amblyopia due to monocular accommodation lag and the validity of this alternative therapeutic approach.
Further investigation on similar cases is needed—if you encounter one, please reach out to me via email.
In some instances, children can intentionally defocus for near vision, thereby releasing their accommodation. While the author finds this unlikely, he does not rule out the possibility that this could be the case. This may represent the only limitation of this clinical case and the dynamic retinoscopy technique.
Conclusions
In cases of amblyopia, it's essential to ensure that optical correction is both optimal and balanced.
For children, visual acuity needs to be measured for both distance and near vision using a suitable, age-related optotype.
Accommodation should be assessed both monocularly and binocularly through an objective method, such as dynamic retinoscopy.
When implementing occlusive therapy for amblyopia, it's important to consider any accommodative lag, which may means additional positive lenses should be used during near-vision tasks (a +2.00D additional lens is recommended)
If you want to view the video material and obtain the original article :
Video 1. : Accommodative Lag
Video 2. : Accommodation is a monolateral or bilateral reflex? Experiment
References
1. Gunton KB. Advances in amblyopia: what have we learned from PEDIG trials? Pediatrics. 2013 Mar;131(3):540-7. doi: 10.1542/peds.2012-1622. Epub 2013 Feb 4. PMID: 23382445.
2. Ale Magar JB, Shah SP. Accommodative Lag Persistence in Treated Anisometropic, Strabismic, and Mixed Amblyopia. J Ophthalmol. 2022 May 10;2022:2133731. doi: 10.1155/2022/2133731. PMID: 35592646; PMCID: PMC9113905.
3. Chen AM, Manh V, Candy TR. Longitudinal Evaluation of Accommodation During Treatment for Unilateral Amblyopia. Invest Ophthalmol Vis Sci. 2018 Apr 1;59(5):2187-2196. doi: 10.1167/iovs.17-22990. PMID: 29801152; PMCID: PMC5916545.
4. Ovenseri-Ogbomo GO, Kudjawu EP, Kio FE, Abu EK. Investigation of amplitude of accommodation among Ghanaian school children. Clin Exp Optom. 2012 Mar;95(2):187-91. doi: 10.1111/j.1444-0938.2011.00692.x. Epub 2012 Jan 19. PMID: 22260310.
5. Hashemi H, Nabovati P, Yekta AA, Ostadimoghaddam H, Forouzesh S, Yazdani N, Khabazkhoob M. Amplitude of accommodation in an 11- to 17-year-old Iranian population. Clin Exp Optom. 2017 Mar;100(2):162-166. doi: 10.1111/cxo.12431. Epub 2016 Aug 22. PMID: 27549747.
6. Singman E, Matta N, Tian J, Silbert D. Association between accommodative amplitudes and amblyopia. Strabismus. 2013 Jun;21(2):137-9. doi: 10.3109/09273972.2013.786737. PMID: 23713938; PMCID: PMC3820007.
7. Guyton DL, O'Connor GM. Dynamic retinoscopy. Curr Opin Ophthalmol. 1991 Feb;2(1):78-80. doi: 10.1097/00055735-199102000-00012. PMID: 10149292.
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