Our eyes, while incredible organs, are not always optically perfect and can have subtle imperfections that go beyond common refractive errors like nearsightedness or farsightedness. These less apparent distortions can significantly impact how clearly and comfortably we see the world. Understanding these more complex visual challenges can help individuals seek appropriate solutions for clearer vision.
Understanding High Order Aberrations
High order aberrations are complex optical imperfections in the eye’s refractive components, such as the tear film, cornea, aqueous humor, crystalline lens, and vitreous humor, that distort how light passes through to the retina. Unlike common vision issues, they are not uniform across the visual field. They can be caused by irregularities in the curvature of the cornea or crystalline lens, or result from scarring due to surgery, trauma, disease, cataracts, or dry eye.
These aberrations differ from “low order aberrations,” which include nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. Low order aberrations account for about 85% of vision issues and are correctable with standard eyeglasses or conventional contact lenses. High order aberrations are more subtle and complex, making up approximately 10-15% of total aberrations in a normal eye, and are not typically corrected by traditional lenses. Over 60 types exist, some with specific names like coma, spherical aberration, and trefoil, while others are identified by mathematical expressions called Zernike polynomials.
Visual Impact of High Order Aberrations
Individuals with high order aberrations often experience specific visual symptoms distinct from the blur caused by standard refractive errors. A common symptom is glare, where bright lights appear overly intense, causing discomfort. This often leads to difficulties with night vision, affecting activities like driving after dark or seeing in dimly lit environments.
Patients may also report seeing halos, which are rings of light around illuminated objects, and starbursts, appearing as rays emanating from light sources. Ghosting or double vision (diplopia) can also occur, where images appear to have faint duplicates or smears. Reduced contrast sensitivity is another frequent complaint, making it harder to distinguish objects from their backgrounds, especially in low light. These symptoms stem from irregular light refraction impacting the quality of the image projected onto the retina.
Detecting High Order Aberrations
Detecting high order aberrations requires specialized technology beyond routine eye exams, which primarily identify common refractive errors. The primary tool for this is a wavefront aberrometer, an instrument that measures the total deviation of light rays as they enter and reflect within the eye.
A wavefront aberrometer projects a flat plane of light into the eye; if the light reflects back as a flat plane, it indicates no aberrations. However, as light passes through the eye’s refractive components, imperfections cause the wavefront to distort into three-dimensional shapes. The aberrometer uses microlenses to measure these deviations at hundreds of points across the pupil, converting them into a detailed 3D map of the eye’s optical imperfections, often represented by Zernike coefficients. This “optical fingerprint” is unique to each individual, providing precise information about the type and magnitude of high order aberrations that traditional methods cannot capture.
Correcting High Order Aberrations
Correcting high order aberrations involves advanced methods beyond conventional eyeglasses or contact lenses, which primarily address lower order refractive errors. Laser vision correction procedures, particularly custom LASIK and PRK, are frequently employed. Wavefront-guided LASIK, for example, uses the detailed wavefront map of the eye’s unique aberrations as a blueprint to precisely reshape the cornea with an excimer laser. This customized treatment can significantly reduce high order aberrations, potentially leading to crisper vision and improved night vision compared to traditional LASIK.
In cases where laser surgery is not suitable or after cataract surgery, specialized intraocular lenses (IOLs) can manage high order aberrations. Some monofocal IOLs are designed with specific spherical aberration profiles to compensate for existing corneal aberrations. While multifocal IOLs can introduce their own aberrations, advancements aim to minimize unwanted visual phenomena like glare and halos. Custom contact lenses, particularly scleral lenses, also offer a solution for high order aberrations, especially for patients with irregular corneal surfaces like those with keratoconus. These large lenses vault over the cornea, creating a stable optical surface with a saline-filled reservoir that helps neutralize corneal irregularities and reduce aberrations.