Multifocal contact lens is a type of lens that provides clear vision at all distances in patients with refractive errors and presbyopia (decline in near vision and related to age). Presbyopia develops in individuals aged 40 and above, and a sign of this includes holding reading material a little farther away due to reduced near vision. A multifocal contact lens can replace reading glasses, which used to be the only remedy to enable near vision in presbyopia patients.
These lenses contain multiple prescriptions in one lens. One prescription takes care of very close objects. In the second one, the individual can view normal objects at a distance, while another prescription can be used for intermediate distance. A person does not need glasses while on multifocal lenses, which offer good near and distance vision. A bifocal design has two lens power for both near and distance vision and is incorporated into the multifocal lens. Multifocal lenses are similar to progressive eyeglass lenses whose lens power is altered gradually, with vision naturally moving from distance to close-up.
Multifocal contacts come in both soft and hard contact lens material. Multifocal lenses made from RGP material offer better sharper vision than soft multifocal contact lenses. However, RGP material is rigid and the individual will require some adaptation and conditioning of the eye for daily wear.
More oxygen reaches the cornea in lenses made from silicone hydrogel material than in the soft contact lenses, therefore, more oxygen means greater comfort. These lenses can be used for both daily and extended (during the night) wear.
The two main multifocal lens types are simultaneous vision designs and segmented designs.
Simultaneous Vision Designs
In simultaneous vision design, the user determines which region provides the sharpest vision to view objects. Specific areas of the lens cater for near, far, and intermediate distances. Simultaneous vision designs are further broken down into two categories; concentric and aspheric.
1. Concentric Contact Lenses
In concentric multifocal contacts, the lens power offers distance vision. Concentric rings (at least two) containing near and distance power surround the lens's center within the pupil area (called center-near designs and center-distance design, respectively). Center-distance design is used to view distant objects and designed for the dominant eye, while the center-near design is meant for the non-dominant eye.
2. Aspheric Multifocal Contact Lenses
Aspheric multifocal contact lenses share comparable characteristics with progressive eyeglass lenses. Multifocal contact lens power increasingly changes from distance to near or vice versa, and from the center to the lens’ periphery. These lenses try to simulate natural sight.
Segmented designs are made from RGP material. They have a smaller diameter than the soft contact multifocal lens and rest on a tear layer above the lower eyelid margin. The multifocal contact lenses allow the wearer to view objects through the lower, near-correction lens’ portion once the individual drops his/her gaze to read or view near objects. These lenses share similarities with bifocal and trifocal eyeglasses where the top and center of the lens are designed with appropriate power for viewing distant objects. Magnifying power is added to the lower part of the lens so that the individual can view near objects. A visible line separates the distance and near zones of the multifocal lenses.
Patience Selection Criteria
Certain ocular aspects affect multifocal contact lens’ performance. The eye doctor evaluates and considers them to select the best lenses. They may include:
- Tear film
- Pupil diameter
- Ocular aberrations
- Off-axis ocular aberrations
- On-eye contact lens performance
Advantages and Disadvantages of Multifocal Contact Lenses
The advantages of multifocal contact lenses include:
- Greater visual acuity for near, intermediate, and far distances
- The patient experiences easier switching between the prescription ranges
- Some lenses are disposable, eliminating the need for contact lens daily care
- It is convenient to see in most circumstances without having to wear anything extra
- Part-time multifocal contact lenses are suitable for occasional wear for those who do not want to wear them every day
Disadvantages of multifocal contact lenses include:
- Difficulties in adjusting because of the different viewing experiences
- The adjustment period may be marked by glare at night or hazy/shadowy vision\
- They may be more expensive owing to the intricate designs and extra measurements