Page 156 - July-August 2020

well. Ideally, the back surface shape diameter as listed below: (see
of the optical zone should have Table 1)
roughly the same shape as the
cornea, at least in theory. This way, Each diameter has a different fit
an even layer of post-lens clearance and helps manage a broad spectrum
shall be visible behind the scleral of patients with a different diagnosis.
lens’s optical zone. To follow the INDICATIONS FOR THE NEED
corneal shape, the back optic zone OF SCLERAL LENSES
can be with a flatter or steeper radii
SCLERAL LENS DIAGRAM Any patient with an irregular
of the curvature.
corneal surface is an ideal candidate
The Transition Zone/Limbal for scleral lenses. It includes patients
MANUFACTURING OF Zone is the zone between the optical with specific diseases and a very high
SCLERAL LENSES zone and the Haptic/Landing zone of prescription. The gas permeable
the lens. This zone sets the sagittal (GP) optics of scleral lenses provide
Earlier the lenses were made
through a moulding process height of the lens. When the trial excellent vision because they centre
(impression method) wherein the sets of preformed lenses are set well, have minimal movement and
mould (cast) is made of the anterior up, the next step up (or down) in are not dependent on rotational
ocular surface and then the cast is sagittal height means an alteration orientation to correct astigmatism.
sent to the manufacturer for making in the Transition zone. It is usually Scleral lenses are a very good
the lens. This method is not quite independent of the Optical Zone and management modality for the
used nowadays as it is cumbersome. the Landing Zone parameters. patients who are intolerant to corneal
With the preformed (trial fitting) The Haptic/Landing Zone is the GP lenses and are dissatisfied with
lenses, trial sets are available which zone that rests over the sclera. It is vision through soft contact lenses.
help the optometrist fit the scleral where the lens actually “fits” and New generation software like
lenses. With the use of computerised makes contact with the eye. The EyePrintPro® etc scan the ocular
lathe cut machines, it is possible for design and characteristic of this surface profile and provide data to
optometrists to make lenses with zone are slightly dependent on the modern CNC machines which allows
submicron precisions. lens category - Landing Zone is a an optometrist to give an accurate

DESIGNS IN SCLERAL LENSES term that is independent of the fit. Such custom lenses eliminate
lens size and where the lens rests. all discomforts like mid-day foggy
A scleral lens typically comprises The back surface geometry of the vision, glare etc. Scleral lenses offer
of three zones - The Optic Zone, The Landing Zone must align with the an excellent vision, and utilises the
Transition Zone, and The Haptic/ scleral shape when fitting full scleral latest technology, materials and
Landing Zone. lenses, or with the limbal shape designs for the patient’s welfare.
when fitting corneoscleral lenses.
The Optic Zone is the central zone It is important to evenly distribute Contact lens practices serve
of the lens that gives the desired the pressure of the sclera to provide patients every day that could benefit
optical effect. The front surface comfort to the patient. from the advantages of scleral lenses.
can be made spherical or aspheric, This modality should be offered as
depending on the requirement of the A scleral lens is sub-divided an option to any patient who may
patients. The surfaces of the aspheric into mini-scleral and full-scleral. benefit, rather than just considered
lens may reduce some aberrations The Scleral Lens Education Society only when nothing else works. Scleral
of the average eye if the lens centres defines scleral lenses via their overall lenses will help the practitioner to
differentiate himself/herself to the
NAME DIAMETER FITTING RELATIONSHIP TABLE 1 patient by allowing them to offer

Corneo-Sclera 12.9 - 13.5 mm Corneal bearing and scleral touch a product that is healthy,
Semi Scleral 13.6 - 14.9 mm Corneal and scleral bearing comfortable, provides excellent
vision and utilises the latest
Mini-Scleral 15.0 - 18.0 mm Scleral bearing and minimal corneal clearance technology, materials and designs.
Full Scleral 18.1 - 24+ mm Scleral bearing and maximum corneal clearance

| JULY-AUG 2020 | 152 CONTACT LENSES