Aphakia is the physical absence of the eye’s natural crystalline lens. This transparent, biconvex structure is positioned behind the iris and contributes approximately 18 to 22 Diopters of the eye’s total refractive power. The lens is necessary for focusing light sharply onto the retina. Without it, the eye cannot converge incoming light rays effectively, resulting in a highly hyperopic, or farsighted, state.
Causes and Risk Factors
The most frequent cause of aphakia is the surgical removal of the lens, usually during a cataract procedure. Cataract surgery involves extracting the cloudy lens. If an artificial lens (IOL) is not implanted afterward, the eye remains aphakic. Although modern cataract surgery routinely includes immediate IOL placement, true aphakia can occur in specific surgical scenarios or due to complications.
In infants and young children, surgeons might intentionally delay IOL implantation following cataract removal. This delay is often due to the rapid growth of the infant eye, which makes accurate IOL power calculation difficult, or to reduce complication risks. Aphakia can also result from severe physical trauma, where a penetrating injury causes the lens to be extruded or absorbed.
A rarer cause is congenital aphakia, where an infant is born without a lens in one or both eyes due to a genetic mutation. The absence of the lens creates a profound optical deficit that requires immediate intervention to ensure proper visual development and function.
Visual Effects and Signs
The missing lens produces two primary functional deficits: extreme hyperopia and an inability to accommodate. The eye loses significant focusing power, leading to a refractive error of +10 to +12 Diopters. This causes distant objects to be blurred. Light focuses far behind the retina, severely impairing both distance and near vision without optical correction.
The second consequence is the total loss of accommodation, the eye’s natural ability to change focus between near and far objects. The crystalline lens achieves this by changing its shape, a mechanism lost when the lens is removed. Consequently, an aphakic eye has a fixed focus point, making reading or close-up work impossible without a strong convex lens addition.
Clinical examination often reveals several distinctive signs. The anterior chamber (the space between the cornea and the iris) appears noticeably deeper because the lens is absent. Another sign is iridodonesis, a subtle trembling of the iris when the eye moves. This occurs because the iris is no longer supported and stabilized by the lens structure behind it.
Correction and Management Strategies
The primary strategy for managing aphakia is the surgical placement of an Intraocular Lens (IOL). The IOL is an artificial, clear lens implanted to replace the focusing power of the natural lens, correcting the high hyperopia. An eye with a successfully implanted IOL is classified as pseudophakic, meaning it has a replacement lens.
If an IOL was not placed during the initial lens removal, a secondary IOL implantation can be performed later. This is the preferred long-term solution for adults, as it provides the most stable and optically superior vision correction. The artificial lens remains inside the eye permanently, offering a fixed, high-quality refractive correction.
For patients who cannot undergo IOL surgery, or for infants whose eyes are still growing, non-surgical methods are used. Aphakic contact lenses provide the next best optical solution, offering superior image quality compared to glasses. These specialized lenses are high-Dk silicone soft or hard lenses with very high plus powers, correcting the refractive error at the corneal surface. Correcting the error closer to the eye’s optical center results in minimal image magnification and a wider, more natural field of view.
Aphakic spectacles, or high-plus glasses, represent the least preferred option for correction. They are necessary when contact lenses or surgery are not feasible, but they introduce significant visual compromises due to the high power required. These thick lenses cause substantial image magnification (often 25 to 30 percent), which can lead to aniseikonia, where the images from the two eyes are perceived as different sizes.
Aphakic glasses also severely restrict the field of vision and produce the “jack-in-the-box” phenomenon. This effect is caused by a ring-shaped blind spot (scotoma) at the edge of the lens, which makes objects suddenly appear and disappear as the eye moves. Despite these drawbacks, high-plus spectacles serve as a functional, albeit optically limited, method to correct severe farsightedness.