Optometrists and Ophthalmologists attempt to ‘correct’ refractive errors and astigmatism when prescribing corrective lenses for glasses and contact lenses. However, as mentioned on another page, glasses cannot compensate for the reduced visual acuity associated with HPS and albinism (Click here). Infact, many people with HPS and albinism gain little from wearing glasses or contact lenses.
The terms ‘best corrected vision’ and best corrected visual acuity refer to the results from tests of visual acuity taken when a patient is wearing lenses that correct for refractive errors and astigmatism.
Refractive errors & Astigmatism
With both Hermansky-Pudlak Syndrome and albinism the shape of the eyeballs and the front of the eye (the cornea) are usually not correct. The shape of the lens in each eye may, also, be incorrect. As a result most people with HPS are long-sighted (hypermetropia), Some may be short sighted (myopia).
In hypermetropia, light entering the eye focuses behind the retina rather than on it as it should do. Without glasses or contact lenses a person will see a blurred image. With myopia, light focuses in front of the retina and this also produces a blurred image. The diagram below illustrates the blurred images seen with varying severities of both conditions
Many people with HPS and albinism will have an ‘Astigmatism’ in which the image from an object is either blurred or distorted from that expected with normal vision. Most people are unaware of this in their daily lives as the brain learns to compensate for some distortions. Astigmatism is usually caused by the front of the eye (the cornea) having an irregular shape. Light from an image is either 1) focused on more than one spot on the retinas so producing a blurred image as with other refractive errors or, 2) is bent causing a distorted image to be seen. These effects can also occur if the lens inside each eye has an irregular shape.