Contact lenses provide better refractive correction of peripheral vision than do eyeglasses. Because the contact lens is closer to the eye than the lens of glasses, a larger proportion of the visual field is able to be refracted with the contact lens.
Contact lenses can be prescribed to correct the following:
Aniseikonia (a difference in image size)
Aphakia (absence of the lens), either congenital or after cataract removal
Keratoconus (a cone-shaped cornea)
Either soft or rigid lenses are used to correct myopia and hyperopia. Toric soft contact lenses (which have different curvatures molded onto the front lens surface) or rigid lenses are used to correct significant astigmatism.
Contact lenses are also used to correct presbyopia. In one approach, termed monovision, the nondominant eye is typically corrected for near vision (reading) and the dominant eye is typically corrected for distance vision. Rigid and soft bifocal and multifocal contact lenses can also be successful, but the fitting procedure is time-consuming because precise alignment is essential.
Neither rigid nor soft contact lenses offer the eyes the protection against blunt or sharp injury that eyeglasses do.
Care and Complications of Contact Lenses
Instructions for hygiene and handling lenses must be strictly observed. Poor contact lens hygiene may lead to infection of the cornea or persistent inflammation.
Lens hygiene includes:
Washing hands thoroughly before inserting and removing lenses
Fully drying hands so no tap water comes in contact with the lenses
Cleaning contact lenses according to manufacturer and doctor instructions
Replacing contact lens case every month
Never rinsing contact lens case with tap water
Keeping the contact lens case away from areas that could be exposed to tap water droplets as amoebae in tap water can cause a severe corneal infection
Discarding residual fluid from contact lens case after contact lens insertion
Leaving the contact lens case open to air dry after contact lens insertion
Never wearing contact lenses overnight
Contact lenses occasionally cause painless superficial corneal changes (eg, epithelial changes).
However, pain when wearing contact lenses warrants careful evaluation. Contact lenses can be painful when:
The corneal epithelium is abraded (see Corneal Abrasions and Foreign Bodies).
The lenses fit poorly (eg, too tight, too loose, poorly centered).
There is too little moisture to keep the lens floating above the cornea.
The lenses are worn in a nonideal environment (eg, oxygen-poor, smoky, windy).
A lens is improperly inserted or removed.
A small foreign particle (eg, soot, dust) becomes trapped between the lens and the cornea.
The lenses are worn for a long time (overwear syndrome).
Complications from wearing contact lenses include:
Corneal neovascularization
Corneal warpage
Corneal edema
Sterile infiltrates
Many of the complications of contact lenses are due to corneal hypoxia which can cause secondary corneal edema, corneal epithelial erosion, and eventually corneal neovascularization. In addition, inflammation (sterile corneal infiltrates) or infection (corneal ulcers) can occur. Symptoms of contact lens-related issues include redness, photophobia, and tearing. Spontaneous improvement in symptoms may occur in a day or so if lenses are not worn if the etiology is mild edema or sterile inflammation. In any condition in which pain does not quickly resolve when lenses are removed, an ophthalmologist or optometrist should be consulted before lenses are worn again.
Infectious keratitis usually presents with eye pain, conjunctival injection, and in contact lens wearers, it is frequently caused by pseudomonas, and staphylococcus aureus, and Acanthamoeba (1). Diagnosis is made by slit lamp examination
Risk factors for contact lens–related corneal infection (keratitis) include the following:
Poor lens hygiene
Overnight or extended wear
Use of tap water in the cleaning regimen
Eyes with a compromised ocular surface (eg, dryness, poor corneal sensation)
Infectious keratitis (corneal ulcer) should be suspected when a contact lens wearer has intense eye pain (both foreign body sensation and ache), decreased vision, redness, photophobia, and tearing. Use of contact lenses increases risk of corneal ulcer. The risk increases approximately 6 to 8 fold if contact lenses are worn overnight (2). Corneal ulcers can be caused by bacteria, viruses, fungi, or amoebae. A corneal ulcer can progress to a potentially vision-threatening infection of the cornea.
Diagnosis is by slit-lamp examination and fluorescein staining. A corneal epithelial defect (which stains with fluorescein) and a corneal infiltrate (collection of white blood cells in the corneal stroma) are present. At times, the corneal defect is large and dense enough to be seen with handheld magnification or even with the naked eye as a white spot on the cornea. Microbiologic analysis of cultures and smears of the corneal infiltrate, contact lens, and contact lens case are indicated. and fluorescein staining. A corneal epithelial defect (which stains with fluorescein) and a corneal infiltrate (collection of white blood cells in the corneal stroma) are present. At times, the corneal defect is large and dense enough to be seen with handheld magnification or even with the naked eye as a white spot on the cornea. Microbiologic analysis of cultures and smears of the corneal infiltrate, contact lens, and contact lens case are indicated.Pseudomonas and acanthamoeba are the most common organisms identified as the cause (3).
Contact lens use should be stopped. Antibiotic eye drops are given empirically for possible bacterial infection. Initial therapy is broad-spectrum, using a fluoroquinolone antibiotic eye drop every 15 to 60 minutes around the clock for the first 24 to 48 hours, then at gradually longer intervals. Additional antibiotic eye drops, such as cefazolin, vancomycin, or concentrated tobramycin, are used if the ulcer is large (> 2mm), deep, or close to the visual axis (Contact lens use should be stopped. Antibiotic eye drops are given empirically for possible bacterial infection. Initial therapy is broad-spectrum, using a fluoroquinolone antibiotic eye drop every 15 to 60 minutes around the clock for the first 24 to 48 hours, then at gradually longer intervals. Additional antibiotic eye drops, such as cefazolin, vancomycin, or concentrated tobramycin, are used if the ulcer is large (> 2mm), deep, or close to the visual axis (4). The antibiotic may be changed or stopped later based on culture results. Neglected cases may respond poorly or not at all to treatment, and severe vision loss may result.
Care and complications references
1. Durand ML, Barshak MB, Chodosh J. Infectious Keratitis in 2021. JAMA. 2021;326(13):1319-1320. doi:10.1001/jama.2021.0424
2. Cope JR, Konne NM, Jacobs DS, et al. Corneal Infections Associated with Sleeping in Contact Lenses - Six Cases, United States, 2016-2018. MMWR Morb Mortal Wkly Rep. 2018;67(32):877-881. Published 2018 Aug 17. doi:10.15585/mmwr.mm6732a2
3. Jeang L, Tuli SS. Therapy for contact lens-related ulcers. Curr Opin Ophthalmol. 2022;33(4):282-289. doi:10.1097/ICU.0000000000000861
4. Lin A, Rhee MK, Akpek EK, et al. Bacterial Keratitis Preferred Practice Pattern®. Ophthalmology. 2019;126(1):P1-P55. doi:10.1016/j.ophtha.2018.10.018
Rigid Corneal Contact Lenses
A rigid lens is able to revise the natural shape of the cornea into a more optimally shaped refracting surface than a soft lens and thus tends to provide more consistent improvement in refraction for people who have astigmatism or an irregular corneal surface. Older polymethyl methacrylate rigid contact lenses have been replaced by gas-permeable contact lenses (GPCLs) made of fluorocarbon and polymethyl methacrylate admixtures. GPCLs are 6.5 to 10 mm in diameter and cover part of the cornea, floating on the tear layer overlying it.
Rigid contact lenses can improve vision in people with myopia, hyperopia, and astigmatism. Rigid contact lenses can also correct corneal irregularities, such as keratoconus. In most cases, patients with keratoconus see better with rigid contact lenses than glasses.
GPCLs are manufactured for individual patients to fit the eye optimally. For complete wearing comfort, they require an adaptation period, typically 4 to 7 days. During this time, the wearer gradually increases the number of hours the lenses are worn each day. Importantly, no pain should occur at any time. Pain is a sign of an ill-fitting contact lens or corneal irritation. Wearers may have temporary (< 2 hours) blurred vision (spectacle blur) when wearing eyeglasses immediately after removing rigid contact lenses.
Scleral Contact Lenses
Scleral contact lenses are made of rigid gas-permeable materials; are larger in diameter than corneal contact lenses; and vault over the corneal surface, with the peripheral portion of the lenses resting on the sclera. They allow a thin layer of fluid to bathe the corneal surface, making these lenses comfortable even in patients with severe ocular surface disease. They are custom-made for each patient and are generally more comfortable and take a shorter time to adapt to than traditional smaller-diameter GPCLs because the scleral lenses do not touch the corneal surface. Scleral contact lenses can correct high degrees of irregular astigmatism (eg, advanced keratoconus).
Soft Hydrophilic Contact Lenses
Soft contact lenses are made of poly-2-hydroxyethyl methacrylate and other flexible plastics (such as silicone hydrogels) and are 30 to 79% water. They are 13 to 15 mm in diameter and cover the entire cornea. Soft contact lenses are often replaced daily (disposable single-use), every 2 weeks, or monthly. Contact lenses should be removed every night to decrease the risk of infection.
Soft contact lenses can improve vision in people with myopia and hyperopia. Because soft contact lenses mold to the existing corneal curvature, anything greater than minimal astigmatism cannot be treated unless a special toric lens, which has different curvatures molded onto the front lens surface, is used. Weighting the lower aspect of the toric lens maintains its orientation by reducing lens spinning.
Soft contact lenses are also prescribed for treatment of corneal abrasion, recurrent erosions, or other corneal disorders (called bandage or therapeutic contact lenses). Prophylactic antibiotic eye drops (eg, fluoroquinolone 4 times a day) may be advisable with a bandage lens. Extended wearing of soft contact lenses, especially in aphakia after cataract surgery, is practical, but an ophthalmologist or optometrist should examine the patient regularly. The patient should remove and clean extended wear lenses at least once a week.
Because of their larger size, soft contact lenses are not as likely as rigid contact lenses to eject spontaneously and are less likely to allow foreign bodies to lodge beneath them. Immediate wearing comfort allows for a brief adaptation period.
Soft contact lenses are associated with a higher incidence of corneal infections than gas-permeable contact lenses, particularly when soft lenses are worn overnight (1). When dry, soft contact lenses are brittle and break easily. They absorb a certain amount of moisture (based on the water content) from the tear film to retain adequate shape and pliability. Therefore, patients with dry eye are usually more comfortable wearing lenses that have a low water content.
Soft hydrophilic contact lenses reference
1. Jeang L, Tuli SS. Therapy for contact lens-related ulcers. Curr Opin Ophthalmol. 2022;33(4):282-289. doi:10.1097/ICU.0000000000000861
