Standard monofocal lens is the most common type of lens used in the treatment of cataracts. It belongs to the category of intraocular lens (IOL). An IOL refers to a small, artificial lens which replaces the natural lens of the eye in cataract surgery. Standard monofocal lens is the most beneficial for patients with cataracts in both eyes.
A standard monofocal lens can only focus on one distance. It can be set to focus for near, intermediate or distance vision but not all three at once. For most individuals, it is set for clear distance vision. These individuals will then supplement vision with glasses for close work or activities that need near vision like reading, cooking, driving, etc.
Standard monofocal lens is made of silicone or acrylic. It is coated with a special material that protects the eye against ultraviolet (UV) rays. The eye's natural crystalline lens has a slightly aspherical shape which enables it to give clear, crisp images. The modern monofocal lens is patterned after this aspherical shape of the natural lens of the eye.
Monofocal lens should not be confused with monovision. In monovision, one eye is corrected for distance while the other one is corrected for near vision. The problem is that because each eye works independently, it can give rise to depth perception. This may force the patient to adjust their gaze as often as possible to allow good vision.
Standard monofocal lens comes in different focusing power just like in contact lenses or eyeglass prescriptions. The doctor measures the length of the eye and the cornea's curve. The measurements are then used to set the focusing power of the standard monofocal lens. The dosage depends on the individual's eye needs. The doctor can prescribe standard monofocal lens for near, mid-distance or distant vision. The focus chosen does not change after surgery.
Toric lens for correcting astigmatism is considered a type of monofocal lens. It may cost more than a conventional IOL. There are also brands of standard monofocal lens which include:
- Aurium monofocal lens - It is photochromatic for it gets lightly tinted during daytime or in the presence of bright light, thus preventing harmful UV rays. Under normal room lighting conditions, this lens becomes transparent.
- Acrysof IQ lens provides excellent vision for distance. It is also fitted with UV protection.
- Aurovue lens is recommended for patients with a low budget.
- Akreos lens is also for low-budget patients.
- Acrysof SP is the preferred lens for diabetic patients.
The purpose of the standard monofocal lens is to function as the natural lens of the eye to provide vision. A cloudy lens with cataract cannot bend light rays entering the eye to enable vision. The result is a hazy, blurry or less colorful vision. Cataract surgery removes this cloudy lens to replace it with a standard monofocal lens, thus improving vision.
Preparation and Expectation Before Surgery
Potential Side Effects
Because lens replacement surgery is more invasive and classified as cataract surgery, there may be complications, risks and side effects such as:
- Patients with monofocal lens may experience visual distortions and halos. However, they are very minimal compared to those having a multifocal lens.
- Persistent inflammation (swelling) of the eye which can result in further complications.
- Retinal detachment which refers to the pulling away of the retina from its normal position. It may happen especially in people who are extremely myopic (nearsighted). It can lead to severe vision loss if not treated.
- Lens dislocation may occur. This would necessitate further surgery to reposition, exchange or remove the lens.
- Intraocular pressure may increase. Also called ocular hypertension, it can lead to glaucoma, a severe eye disease that can cause loss of vision or total blindness.
- The eye may bleed or develop an infection. Infections may be serious and require immediate attention.
- Ptosis (droopy eyelid). Ptosis occurs when the upper eyelid droops over the eye. Severe ptosis can block normal vision.
- Cystoid macular edema. It is the swelling of the retina which can lead to blurry or decreased vision.
A standard monofocal lens is stored in a vapor-permeable package. It should be kept in a relatively dry environment and at room temperature. Studies have concluded that the context in which the lens is stored will determine its effectiveness. For instance, one study found that spraying an environment in which the lens is stored can cause surface changes to the lens. Hence, when spraying to disinfect or clean a storage room, the lens should be moved to a safer environment that has no chemicals.