What are scleral lenses
Scleral Contact lenses are large diameter Lenses that are often used with patients who can’t be helped with regular soft contact lens and RGP lenses. They rest on the white part of the eye, completely covering the cornea and are used to correct refractive error in eyes with irregular cornea. The size ranges from 14.5 mm to 23 mm.
History of Scleral Lens
The first idea of contact lenses was conceptualised by Leonardo da vinci in 16th century, but the first model of scleral lenses were made in 1887 by Fredrich A Muller and Albert C Muller using blown glass. In 1888, Eugene Fick and Eugene Kalt theorised addition of optics in these lenses for vision correction, which was later used by August Mueller for his high myopia.
The glass material was gradually replaced with PMMA and other materials that allowed good oxygen permeability. This helped scleral lenses overcome previous issues of corneal hypoxia, short wearing time and discomfort. The scleral lenses now use high DK lens materials and provide much better comfort and ocular health than before.
How Scleral Contact Lens work?
Scleral lenses, by definition, sit on the sclera – the conjuctival scleral complex, to be precise. They completely cover the cornea and the limbus, thereby providing an even anterior surface to the ocular optical system.
These lenses have three zones – optical zone, transition zone and the landing zone. The landing zone rests on the conjunctival scleral complex and usually consists of three curves. It presses down on sclera and creates pressure. The optical zone contains the prescription for vision correction, and the transition zone merely works to bring these two zones together to maintain an optimal fit.
Scleral lenses are filled with saline and then fitted into the eye. The distance between cornea and the posterior surface of lens is known as vault. They sit on the conjunctiva and provide an even corneal surface. Scleral lenses can be worn for 12-14 hours per day, and has a lifespan of 1-3 years.
Who is it used for
Scleral lenses are mostly used for patients with irregular cornea. Since the lenses do not touch the corneal surface, they are able to correct the vision without further scarring the eye. For many patients, these lenses are the last resort since their vision cannot be managed with spectacles, RGP or soft contact lenses. Patients with Keratoconus and other forms of corneal ectasia, corneal dystrophies and degeneration, and corneal scars will be benefitted with use of these lenses.
They are also used to manage ocular surface diseases like severe dry eyes (scleral lenses for dry eye), corneal neurotrophy, keratitis. Patients with steven Johnson syndrome, sjogren syndrome often present severe dry eyes and neurotrophy.
They can also be used to manage post-surgical complications. These lenses are used to correct lasik-induced irregular astigmatism and dry eyes. They protect the eye from environmental irritants and help prevent further damage.
Insertion and Removal
- To insert the lenses, Rinse the lenses first with saline.
- Place the lenses between the middle finger, forefinger and thumb. This is the tripod method. Alternatively, you can also use a plunger. It is a small suction tool used to insert and remove the scleral lenses.
- Fill the lenses with saline solution upto the rim to prevent any air bubbles. Then insert directly on the center of eye in a facedown position.
- When using hydrogen peroxide as a solution, you must wait for at least 6 hours after placing lenses in storage cases to neutralise the solution
- To remove the lenses, artificial tears are first inserted to loosen the lens.
- Then hold the eyelids wide while looking down and and push down the eyelid. This removes the pressure and lenses can then be safely removed
- Plunger can also be used. Attach the plunger to the bottom of the lens, and remove the lens by pulling it out.
- Do not use the plunger in the middle of the lens or apply too much pressure while removing it.
Advantages
Since these lenses do not touch cornea, it stops the scar from worsening. They’re more stable in eye and don’t irritate eyes as much as RGP or soft contact lenses. Similarly, they can be used for any degree of corneal irregularities.
Disadvantages
The major disadvantage of scleral lenses is the amount of time it takes to achieve proper fitting. Scleral Lenses need to be custom made for each patient, and needs expertise for fitting.
Due to this, the scleral lenses can also be costly.
The saline in these lenses can collect debris over time, which makes the lens dirty.Midday fogging is the accumulation of debris in posterior surface or lens that causes the vision to be foggy. It will require the patient to remove and clean the lenses, which can be challenging for patients.
Scleral lenses have to be used with caution when used on patients having endothelial dystrophy, corneal edema or neovascularisation. Patients who are prone to corneal epithelial abrasion need to be careful since the use of scleral lenses can further weaken the epithelium. Patients with low endothelial count are also contraindicated for scleral lenses.
Similarly patients with small eyes and palpebral fissure might have some difficulty with fitting of the scleral lenses. Scleral lenses cost depends upon the brands, material and oxygen permeability.
Article By: Manashwi Karki, Optometrist
