(Semi-) Scleral lenses

With irregular cornea surfaces, problems with standard contact lenses arise. With the semi-scleral contact lens a solution has been designed for this problem. It has a supporting edge of 2 mm on the sclera and a cornea part that consists of 3 separate curves. In total semi-scleral lenses have diameters of 22 to 25 mm. Normal cornea lenses vary their diameters between 8 and 12 mm.
To properly compute the lens curves, the department of medical physics from the University of Amsterdam has developed the formulas with which this lens can be produced.This lens is very successful because the sclera bears the pressure of the lens, thereby relieving the cornea. The sclera is far less sensible and therefore the lens is more comfortable.

SEQ lenses are an extension of the indication area for contact lenses. If the eye care professional sees problems he cannot solve for the patient then there are two optical possibilities:

1. Ophthalmic surgery
2. SEQ lenses

Contact lens problems are more prevalent among irregular cornea surfaces. Using a soft lens underneath a RGP lens we can often increase support, so the tolerance of the RGP lens is positively affected. A drawback is that the patient has to carry two lenses and therefore a dual supply system. It also appears that, especially in older patients, the handling of SEQ lens is much simpler instead of using a soft lens in combination with an RGP lens.

Which indications may cause an irregular surface? To name just a few:

• Keratoconus / perforating keratoplasty in whole or in part from level (tilted plastic can also bring very complex applications with them).
• Lagophthalmus, some eyes remain open too far that even mega soft bandage lens fall out spontaneously.
• Symblepharon patients with overall lens diameter may be smaller caused by adhesions; a standard bearing edge of 2.0 mm should be chosen.
• Patients with Hyper innervations of the MM.
• Frontales.
• Trauma/herpes or Keratitis
• Indications for watch glass connections.
• Corneal protection during eyelid surgery.

The lens design is called ‘SEMISCLERAAL-CONTACT “abbreviated, SEQ. This lens has as its starting point, a bearing edge of the sclera at the corneal 2.0mm part consists of three curves. The SEQ lens features 10 fenestrations, which prevents the lens getting stuck. Irregular corneal surfaces are corrected using RGP contact lenses, corneal lenses ranging in diameter from 8.0mm to 12.0mm. (Whether or not with a double) sclera lenses vary in diameter from 22.0mm to 25.0mm.

To build up the lens and final fitting, the medical physics department of the University developed formulas that are used for the calculation and production of the lens. To narrow the whole range it begins with a sagitta fitting set of 2.70mm extending to 4.10mm. Differences in the fitting set are similar to a fitting set for RGP lenses with a different radius of 0.05mm between a normal step.

The SEQ fitting set expires with sagitta 0.1mm height difference. It is clear that despite the DK value of 90 (at request 125), and 10 times fenestration of SEQ lens, an oxygen supply problem persists. Lenses adjusted in diameters larger than 12.0mm have a lot of support that it is not moving and thus no tear exchange can occur.

As a precaution we advise the patient wearing the lenses half the time of the lenses once to take off and rinse immediately to work.

To understand the effect well, please see the above figure; as it shows a side view drawn from a sample sagitta.

The success of the lens lies in the fact that the lens contributes to the sclera so that the pressure of the corneal lens is reduced or completely preventable, the sclera has a lower sensitivity and can tolerate a lot more pressure.

The patient is asked to look right / left / up and down so that with a low  magnification an evaluation can take place; if the fluorine in the bearing edge is actually pushed away.

The above picture shows a too small sagitta provides a first protruding edge can be seen at 6 hours. In one situation when sagitta magnification leads to bubbles the 6 hour zone can be truncated.