Dr. Nir Erdinest-Mini scleral contact lenses
The mini scleral contact lens is the most common design for appliers of scleral contact lenses in Israel and the USA.
While scleral contact lenses appliers in Europe prefer the design of the full-sized scleral lens. The radius of the mini scleral lenses range from 15mm to 18mm (regular rigid contact lenses are usually up to 10mm).
Mini scleral contact lenses in comparison to full-sized scleral contact lens
Mini scleral contact lenses are spacious and provide minimal corneal contact when compared to a full scleral lens. Scleral contact lenses provide a relative contact area that is considered to be mediocre with sclera and therefore the lens landing area is narrow compared to scleral contact lenses.
In a full-size scleral lens with a diameter of 18.0mm to 24mm, we receive full corneal clearance and a wider area of contact with the sclera. It is logical that only lenses above 18.11mm are full scleral contact lenses.The definition states that 18.8 mm lenses are also full scleral contact lenses. Commercial companies do not produce lenses of 18.11mm and therefore it was agreed that 18mm and above maintains the definition of full scleral lens.
Full-size scleral lenses are easier to fit in very complex corneas because the cornea is very convex. The lens should be rigid enough regardless of size or shape of the lens to avoid lens flexibility.
Holding the mini-scleral contact lens
When holding the lens between the thumb and the forefinger and applying moderate pressure, the lens should not bend. If the lens is flexible, there is a chance that negative pressure will be generated under the lens, unless the adjusted lens is significantly flat to prevent an opaque system. Negative pressure under the lens may cause limbal swelling and visual distortion
Fitting mini-scleral contact lens
A scleral lens fitting is based on the sagittal depth below the lens, compared with the corneal sagittal depth of the cornea. The factors affecting the sagittal depth of the lens and the cornea include corneal curves, peripheral curves, corneal diameter, lens diameter, and corneal diameter. Two different patients may have the same cartometric values, but if one eye is smaller, the sagittal depth will be significantly smaller. Cornealaclars designs or semi-scleral designs require a slightly more nominal depth relative to the cornea. Just as the corneal lenses are slightly more flat than the flat meridian of the cornea in order to prevent the lens from reaching the cornea or to prevent the adhesion phenomenon. For a mini-scleral lens, minimal sagittal depth is required, while full scleral lenses require a large sagittal depth and maximum spacing from the cornea. When we choose a lens design, we must remember the desired corneal spacing considering the lens diameter.
Choosing a mini-scleral contact lens
The choosing of the lens from the set is performed with a quick glance from the side (corneal profile) and the assessment of the corneal and scleral angle. Then the lens and bubbles are examined and the final assessment is done using the fluorescence image in general (iris cover) and the depth assessment. The depth assessment is performed using optic section under white light in slit lamp. The comparison is made in relation to the thickness of the raw material of the lens against the thickness of the fluid that actually constitutes the sag.