Amblyopia, otherwise called lazy eye, is a frequently encountered condition nowadays due to a large number of undetected and uncorrected refractive errors. It most commonly occurs in children than in adults.
What Is Amblyopia?
Amblyopia occurs due to continuous or frequent deprivation of the visual-sensory stimulus of the light-sensitive layer called the retina. When one eye sees a clearer image of the object and the other eye sees a blurred image of the same object, the brain may try to make the eye see clearly. But after a while, the brain “shuts off” or neglects blurred inputs from the affected eye and this eye in due course becomes a lazy eye. It most commonly occurs unilaterally and is rarely bilateral.
Causes:
– Ametropia:
Uncorrected refractive errors occur most commonly in children, especially when one eye has a refractive error while the other eye is normal. The children don’t sense the difference since the normal eye compensates except for the depth of perception.
– Anisometropia:
When the difference in the refractive error between the two eyes is larger (mostly greater than 1.5 dioptres), the eye with a higher power goes in for amblyopia.
– Strabismus:
Otherwise called squint, this is the most common cause (along with anisometropia). In this condition, the eyes are misaligned. The vision is worse in the consistently deviating/non-fixing eye leading to amblyopia. Squint can lead to lazy eyes and vice versa.
– Media Opacity:
For the eye to sense an image of an object, the light from the object should travel through all the transparent structures inside the eye to reach the retinal focus point (fovea centralis). Any opacity in the pathway of light like a corneal scar due to injury/infection, lens opacity due to cataracts, etc. can lead to sensory deprivation of the eye leading to amblyopia.
– Occlusion Amblyopia:
This happens due to prolonged patching therapy of the fellow eye. This is prevented by periodic vision analysis and examination by a specialist.
When to Approach a Doctor?
★ When vision in one eye is constantly blurred compared to the other eye.
★ In children, a unilateral lazy eye is difficult to detect, usually noticed by parents when a child develops squinting/head tilt/closing the blurred eye while visualising. Sometimes, lazy eye is detected during a periodic eye check-up/school health check-up.
Tests Done for Lazy Eye:
❖ Vision analysis.
❖ Patients find reading individual letters easier than an array of letters (crowding phenomenon).
❖ Eye examination. (To rule out organic causes causing decreased vision.)
❖ Cover-uncover test done for squinting and to assess the degree of squint.
❖ Cycloplegic refraction for young children.
Treatment:
Treatment for amblyopia is a prolonged one and depends on the compliance of the patient with the suggested treatment.
👁️🗨️ For Ages Less Than 12 Years
- Appropriate spectacle correction
- If vision remains reduced even after a period of refractive adaptation (6-12 weeks usually), penalising of the fellow eye is done.
- Patching: It is done in the better-corrected eye for 2 to 6 hours per day for a week as per the age of the child. E.g.: 3 weeks for a 3-year-old child and 4 weeks for a 4-year-old child.
- An adhesive patch applied directly over the eye is the most preferred. If it causes local irritation/skin allergy, applying a tincture of benzoin on the skin before applying the patch and using a warm water compress over the patch before removal is advised.
- Alternatively, a patch can be applied over the glasses that the child wears as long as the child does not peek around the patch. Frosted glasses are also available for the same purpose.
- In rare cases of bilateral amblyopia, alternative patching is done. Parents are advised on the duration of patching on each eye to avoid occlusion amblyopia and periodic eye check-up is advised.
- Penalisation with Atropine: This method is as effective as patching in mild-moderate amblyopia.
- Optical Degradation: This is done using a hyperopic lens in front of the fellow eye to blur the image or in high myopia removal of minus lenses from the preferred eye.
- Patients are advised to continue patching till the vision is equalised in both eyes or no improvement after 3 compliant cycles of patching.
- In lazy eyes due to squinting, squint surgery is usually deferred till the vision in both eyes is equal or maximum vision is obtained in the amblyopic eye.
- If vision in children does not improve beyond 6/12 or 20/40, the child should be given eye protection during sports (one-eyed athlete rule).
👁️🗨️ For Patients Outside Treatment Age
- Best spectacle correction
- Patching trial
👁️🗨️ Any media opacity if present is treated accordingly and patching of the fellow eye is continued for visual equalisation.
Dr. Sudha Bhuvaneshwari
Associate Consultant in Ophthalmology
Kauvery Hospital Chennai
