Vision correction plays a significant role in improving the quality of life for many individuals. Some people are born without a natural eye lens, or have it removed due to injury or disease, a condition known as aphakia. This absence of the lens severely impairs vision, making everyday tasks challenging. Aphakic contact lenses offer a solution, acting as a primary means of vision restoration for these individuals.
What is Aphakia?
Aphakia describes the condition where the eye’s natural crystalline lens is absent. This lens, typically located behind the iris and pupil, is responsible for focusing light onto the retina, which is necessary for clear vision. Without the lens, the eye cannot properly focus light, leading to significant visual disturbances.
The absence of the lens can stem from various causes. Congenital aphakia is a rare condition where an individual is born without a lens due to developmental issues during pregnancy. More commonly, aphakia is acquired, primarily following cataract surgery where the cloudy natural lens is removed without implanting an artificial intraocular lens (IOL). Trauma to the eye can also cause the lens to dislocate or be expelled, resulting in aphakia. The absence of the lens causes extreme farsightedness (hyperopia) and a complete loss of the eye’s ability to adjust focus between different distances, known as accommodation.
How Aphakic Contact Lenses Work
Aphakic contact lenses function by replacing the focusing power of the missing natural lens. These lenses possess a very high positive power, which is necessary to compensate for the severe farsightedness that characterizes aphakia. By placing this strong convex lens directly on the corneal surface, light rays are converged and brought to a sharp focus on the retina, allowing for clearer vision.
The placement of the contact lens on the eye’s surface, rather than in spectacles, offers optical advantages. It significantly increases the depth of focus for the aphakic eye, enhancing visual efficiency across various distances, especially for near vision. This “positive efficiency” for near vision is a notable benefit, as it helps to restore some ability to focus on close objects, which is otherwise lost due to the absence of the natural lens and its accommodative function.
Types of Aphakic Contact Lenses
A variety of aphakic contact lenses are available, designed to meet diverse patient needs. These lenses are categorized by their material, wear schedule, and specific design features. Common materials include silicone elastomer (SE), which offers very high oxygen permeability, and rigid gas permeable (RGP) materials.
Silicone elastomer lenses, such as Silsoft, are frequently used, particularly for infants, due to their high oxygen transmission and suitability for extended wear. Rigid gas permeable lenses are another option, known for their ability to correct astigmatism and provide consistent vision, though they require daily removal. Custom soft lenses, including silicone hydrogel lenses, are also available, offering high oxygen permeability and greater comfort for some patients.
Living with Aphakic Contact Lenses
Proper management of aphakic contact lenses involves a careful fitting process, consistent handling, and diligent care routines. An ophthalmologist or optometrist conducts the fitting, which includes assessing the eye’s refraction to determine the lens power, often factoring in vertex distance. For infants, a slight over-correction to induce mild myopia is used, as their primary visual interest is at close range.
Insertion and removal techniques are taught by eye care professionals, and adherence to these methods is important to prevent complications. Daily care involves cleaning the lens by gently rubbing both sides with a recommended solution, followed by thorough rinsing. Lenses should be disinfected by storing them in their case overnight with fresh solution; tap water or saliva should never be used. Regular follow-up appointments are important for monitoring eye health and adjusting lens parameters as needed, especially for infants due to rapid eye growth and refractive changes. Common challenges can include handling difficulties, an initial adaptation period, and potential issues like dryness or the risk of infection if care routines are not followed.
Alternatives to Aphakic Contact Lenses
While aphakic contact lenses are a common solution, other vision correction methods exist for aphakia. Intraocular lens (IOL) implantation involves surgically placing an artificial lens inside the eye, often at the time of cataract removal. This surgical option provides a permanent correction and eliminates the need for daily lens handling.
Aphakic spectacles, or eyeglasses with very thick lenses, can also correct the severe farsightedness. However, these glasses cause significant image magnification, peripheral distortion, and a reduced field of view, which can be challenging for the wearer. Contact lenses are preferred over spectacles, especially for infants and young children, because they provide a more natural image size and field of vision, which is beneficial for visual development. For very young children, IOL implantation may be delayed due to rapid eye growth and the increased risk of complications in infants, making contact lenses a more practical and adaptable temporary or long-term solution.