The test combines the principles of preferential looking and vanishing optotypes, in which the value given is converted to Snellen equivalent. The test uses pictures that will interest a child (a house, car or duck for example) positioned either at the top or at the bottom of an otherwise grey card. There are eleven visual acuity levels, with three cards at each level.
For even younger babies, I usually test their vision with toys, small object like raisins or a“hundred & thousand” sweet test. If the child is able to pick up a small sweet at 33cm, visual acuity is at least 6/24 or 20/80.
The second major test is a Refraction Test. Refraction is a process your eye-care professional uses to measure your refractive error or vision problem. For children 4 years and older or those able to co-operate, an autorefractor will be used to provide an objective measurement of a person’s refractive error and prescription for glasses or contact lenses.
During a comprehensive eye examination, the ophthalmologist will use refraction to determine how much power is needed to get your child perfectly focused vision. The comprehensive test consists of objective refraction and subjective refraction.
An objective refraction is a refraction obtained by using different instruments, such as retinoscope or auto-refractor, without receiving any feedback from the patient.
A subjective refraction requires responses from the patient. Your doctor may use a phoropter to measure your subjective refractive error.
A cycloplegic refraction is a procedure used to determine a person’s complete refractive error by temporarily paralyzing the muscles that aid in focusing the eye. Sometimes eye doctors prefer to obtain this when trying to obtain an accurate refraction in young children who may skew refraction measurements by adjusting their eyes. To temporarily paralyze or relax the focusing muscle of the eyes, cycloplegic eye drops are used. To get the full cycloplegic effect or total paralyzing of the eye muscle, more than a drop might be needed especially in heavily pigmented eyes, typical in Asian patients. I will usually combine cycloplegic drops and dilating drops.
Here is the worst bit.. the cycloplegic drops will sting! Most of my little patients often cried when this drop is applied. I usually try to reduce the discomfort by instilling a numbing local anaesthetic drop which, ironically according to the children, also sting!
When a cycloplegic refraction is performed, the doctor can know what the full refractive error is without any influence of the person being tested. For example, the patient may be subconsciously over-focusing. This may makesomeone appear more near-sighted or less farsighted than they are.