Typical contact lenses may not be comfortable if you have keratoconus, and especially if you tend to have “dry eyes” or eye pain. Ever since the introduction of disposal soft lenses in 1987, these have been the the predominant type of contact lenses purchased by adults in the US (but these cannot correct astigmatism, which is common in near-sighted people with keratoconus). Meanwhile, a past history of cornea surgery can preclude the use of either soft or “hard” contact lenses. Fortunately, scleral lenses can enable the use of contact lenses by many keratoconus-afflicted adults unable to wear typical contact lenses.
The following describes the primary differences between typical contact lenses and scleral lenses, as well as the three types of scleral contact lenses. If you are uncertain as to whether scleral lenses can improve your vision as an adult with keratoconus, scheduling an appointment with the Precision Keratoconus Center is an excellent “first step” in the process of acquiring that knowledge.
Difference Between Typical Contact Lenses and Scleral Lenses
Placed over the lens of each eye, typical contact lenses float on the tear film on the surface of the eye (per the American Academy of Ophthalmology). Therefore, both soft and “hard” lenses rest on the cornea. In contrast to typical contact lenses, scleral contact lenses cover the entire cornea, which is why these are often more comfortable for people with cornea disorders (such as keratoconus).
The National Keratoconus Foundation notes the following as three advantages of scleral contact lenses as compared to typical contact lenses:
- Less likely to fall out of eye;
- Less likely to have dust or dirt particles slide under them during wear;
- More comfortable because lens edges rest above (and below) the eyelid margins
Overall, scleral contact lenses are larger in diameter than typical contact lenses.
Option Number 1 – Corneo-Scleral or Semi-Scleral Lenses
This type of scleral lens rests near the junction between the cornea and the sclera, and covers a smaller portion of the sclera than occurs with full scleral lenses. Corneo-scleral (semi-scleral) lenses also typically have a smaller tear reservoir than full scleral lenses.
According to study findings published in 2018 in Contact Lens and Anterior Eye, semi-scleral lenses demonstrated lesser reduction in the tear meniscus area and lower induced hypoxic stress. However, this article also concluded that the osmolarity levels were equally good with both types of scleral lenses.
Option Number 2 – Mini-Scleral Lenses
In contrast to other scleral lens types, mini-scleral lenses vault over the entire surface of the cornea, and rest on the anterior sclera. An article in Clinical Ophthalmology reported that mini-scleral lenses often have a diameter between 15-18 mm. Therefore, mini-scleral lenses have less corneal clearance than other scleral lenses. The authors of this article also noted that full scleral lenses most often have a diameter of at least 18 mm.
Meanwhile, an article in the Journal of Optometry concluded that min-scleral lenses were useful in patients with ocular complications due to Graves’ disease.
Option Number 3 – Full Scleral Lenses
These are the largest of the three types of scleral lenses, and provide the greatest amount of clearance between the back surface of the contact lens and the cornea. Similar to semi-scleral and mini-scleral contact lenses, these require filling the bowl of the lens with a saline solution prior to insertion in the eye. This is the type most frequently recommended for keratoconus-afflicted adults who have experienced previous corneal surgeries. Furthermore, it may be the most preferable for adults with corneal disorders and persistent “dry eye” problems.
The professionals at the Precision Keratoconus Center can assist you in acquiring a better understanding of the advantages and disadvantages of each of these types of scleral contact lenses.