Diopters and Lens Power

Refractive error is measure by retinoscopy.he examiner uses a retinoscope to shine light into the patient’s eye and observes the reflection (reflex) off the patient’s retina. While moving the streak or spot of light across the pupil the examiner observes the relative movement of the reflex or manually places lenses over the eye (using a trial frame and trial lenses) to “neutralize” the reflex. . Myopes display an “against” reflex, which means that the direction of movement of light observed from the retina is a different direction to that in which the light beam is swept. Hyperopes, on the other hand, display a “with” movement, which means that the direction of movement of light observed from the retina is the same as that in which the light beam is swept. Static retinoscopy is performed when the patient has relaxed accommodative status. This can be obtained by the patient viewing a distance target or by the use of cycloplegic drugs (where, for example, a child’s lack of reliable fixation of the target can lead to fluctuations in accommodation and thus the results obtained). Retinoscopy is particularly useful in prescribing corrective lenses for patients who are unable to undergo a subjective refraction that requires a judgement and response from the patient

McLatchey noted that gender had no impact on myopic shift in pediatric cataract patients
Unilateral cataracts have longer axial lengths than bilateral (Trivedi), and a higher rate of myopic shift

Type of cataract dodesn’t influence growth

The refractive error at corneal plane of an aphakic eye at age one moth can be anywhere between +19 and +38 with an average of about +31. There is rapid growth in the first 18 months of life, leading to an increase in corneal radius and frequent changes are required. The greatest increase in corneal radius occurs in the first three months between .2 and .8 mm, with an average approaching that of an adult 7.8 mm by age 3. For unilateral aphakics the rate of change per month was .43 d for each month between 1 and 6 months, .37 between 6 and 12 months and .3 between 12 and 18, and .24 D between 18-24 then .19 thereafter. Corneal flattening occurs faster in aphakic eyes than normal. Eyes with cataract have far more rapid growth in axial length after removal than non apakic eyes. Since corneal power remains relatively constant in the first year- changes in axial length are the most important metric,. Typical 10 Diopter shifter from childhood to adult, though those that underwent surgery in first three months had a reduced shift. Weakley et al reported a mean myopic shift of about 8 D from 1 month post op to 5 years old. The mean rate of change in a myopic direction from 1 month after cataract surgery up until age 1.5 years was 0.35 D/mo (95% CI = 0.29,0.40 D/mo); after age 1.5 years the mean rate of change in a myopic direction was 0.97 D/yr (95% CI = 0.66, 1.28 D/yr). The mean refractive change at age 5 years for children 1 month of age at surgery was 8.97 D (95% CI, 7.25, 10.68 D) and for children 6 months of age at surgery was 7.22 D (95% CI, 5.54, 8.91 D). The mean refractive error at age 5 years was −2.53 D (95% CI, −4.05, −1.02 Data from 330 eyes of 165 subjects were included in the study. The mean age at the time of examination was 30.62 (SD 18.04)mo. The steepest increase in axial length was present during the first 10mo of life. After 36mo, there was no statistically significant axial length growth

Considering an approximate overcorrection of +2 D and the availability of SilSoft CL powers, we recommend a 32-D CL when the preoperative AL was less than 17 mm, a 29-D Cl when the preoperative AL was between 17 and 18.5 mm, a 26-D CL when the preoperative AL was 18.5 to 19.5 D, a 23-D CL when the preoperative AL was between 19.5 and 20 mm (21 mm), and a 20-D CL for an AL of 20 to 21 mm (20 D for >21 mm). These power suggestions are a starting point before the necessary retinoscopic overrefraction. When the CL power falls between available powers (SilSoft Super Plus lenses are available in 3-D steps), customized decision should be made by the physician. For example, what if an eye requires 30.5 D? A +32-D CL can be chosen because the infant’s visual needs are mostly at near. However, a +29-D CL can be chosen if the CL will be replaced in the near future because it is likely that the eye will grow very fast in this age group and soon this eye will require a +29-D CL.

For IOL an important factor to consider is the projected growth of the eye. The ideal IOL Power should give the best help for fighting ablyopia while inducing the least refractive error in adulthood. Initial hyperopia should be low enough to be corrected by either a concat lens or glasses.

A typical refactive error for an aphakic infant is +32, a six year old is +23 and adult is +13. Contact lenses are treament of choice. Whenever possible use retinoscope with cyclopegia to determine refraction. Compensating for vertex distance. A calculated prescription of +24 on spectacle plane would translate to +29 contact. Factor in working distance. Most visual development of baby occrus at 1-3 feet so add +1 to +3, moving out as school starts. s.⁷ Consequently, they should be overcorrected to focus vision on a near viewing point and to account for their so-called near world.^8,9 Various studies have used an addition of +4 to +2 D. 

Within the CL parameters available, the authors indicated the following silicone elastomer lens powers for the corresponding ages: 0 to 6 months, +29 D; 7 to 17 months, +26 D; 18 to 28 months, +23 D; and 29 to 34 months, +18 D.⁵ Moore noted that the mean spherical equivalent refractive error for these patients was +28.5 D at 6 months, +26.5 D at 12 months, +23 D at 24 months, and +21.5 D at 36 months.⁶  This model suggests change of 3.2 D per 1 mm of AL

Tiral lenses are a must for fitting patients until feasibly obtian keratometry readings fititing can establish corneal curvature. Micropthalmia are highly myopic and have a steep cornea.