The following guide outlines how to fit the EyeSpace Scleral lens using five easy steps:
Step 1: Lens Diameter
Step 2: Lens SAG@15mm
Step 3: BOZR
Step 4: Scleral Landing Zone
Step 5: Lens Toricity
Step 6: Back Vertex Power
Note: Do not fit the EyeSpace Scleral lenses empirically. Use the EyeSpace Scleral diagnostic lenses to confirm optimal lens fitting parameters on the eye before ordering the final lenses.
Step 1: Lens Diameter
The EyeSpace Scleral 2 lens should always vault the limbus. To achieve limbal clearance the EyeSpace Scleral 2 lens can be ordered in various lens diameters ranging from 16.50 mm to 20.00 mm in 0.50 mm steps. To calculate the lens diameter add 5.50 mm to the measured HVID and round up to the nearest 0.50 mm.
Lens Diameter = HVID (mm) + 5.50 mm
= 11.40 mm + 5.50 mm
= 16.90 mm (round up tp the nearest 0.50 mm)
Step 2: Lens SAG@15mm
The SAG@15mm value controls the sagittal height (depth) of the EyeSpace Sclera 2 lens and ultimately the corneal apical clearance (post-lens tear film thickness).
- Optimally, the lens should vault the corneal apex with 100 - 150 microns of post-lens tear thickness (PLTT) clearance after settling. With slit lamp observation the PLTT should be 0.5:1 to 1:1 the thickness of the lens in the centre.
Note: The central lens thickness can vary due to lens power. Lenses with plus BVP and/or front surface cylinders will be much thicker in the centre compared to lenses with high minus BVP.
- The post-lens tear thickness (PLTT) at any aftercare should never be less than 100 microns.
- Changing the BOZR, lens diameter, and SLZ does not influence the total sagittal height (depth) of the lens.
- Various methods can be used to calculate the initial SAG@15mm value of the EyeSpace Scleral diagnostic lens including; topography SAG@10mm, the Smith Technique, the corneal condition sagittal height table, and trial fitting with a diagnostic lens set.
- In extreme cases of large SAG@15mm values, larger lens diameters are required.
Step 3: Back Optic Zone Radius (BOZR)
- The simplest method for selecting the optimal BOZR is to select the best fit sphere from the elevation map or contact lens fitting software on the corneal topographer.
- The BOZR should have a uniform clearance over the central 8.00 mm corneal zone.
- The BOZR is fitted to align the corneal curvature, much the same as an alignment fit RGP lens.
- Using OCT or slit lamp observation with fluorescein it is possible to judge if the BOZR provides a uniform clearance over the central 8.00 mm zone of the cornea.
- A BOZR that is too steep has more clearance over the central cornea in comparison to 4.00 mm out from the corneal centre, thus creating a convex or plus power post-lens tear layer.
- A BOZR that is too flat has less clearance over the centre than at 4.00 mm from the centre, creating a concave or minus tear layer profile.
- The BOZR can be made toric for improved central corneal fitting for eyes with high central corneal astigmatism, for example, Keratoconus and Pellucid Marginal Degeneration.
Step 4: Scleral Landing Zone (SLZ)
- The SLZ is designed as a hyperbole to provide a gentle but wide landing zone on the para-limbal sclera.
- A useful analogy is to describe the SLZ as a foot, with the ‘toe’ as part of the SLZ nearest to the lens edge and the'heel' nearer to the limbus. As the conjunctiva is relatively soft and the lens will depress into the conjunctiva, it is important the lens lands with a wide and even footprint.
- When assessing the SLZ look in all quadrants and pay attention to the lens edge for blanching of blood vessels running under the SLZ at either the lens edge (toe) or nearer to the limbus (heel).
- The SLZ can be specified to have a flatter or steeper angle and can be ordered as rotationally symmetrical, toric or quadrant-specific to allow optimal peripheral alignment.
The SLZ angle can be ordered with the following parameters:
- 9+ Flat (31°)
- 8+ Flat (32°)
- 7+ Flat (33°)
- 6+ Flat (34°)
- 5+ Flat (35°)
- 4+ Flat 36°)
- 3+ Flat (37°)
- 2+ Flat 38°)
- 1+ Flat (39°)
- Standard (40°)
- 1+ Steep (41°)
- 2+ Steep (42°)
- 3+ Steep (43°)
- 4+ Steep (44°)
- 5+ Steep (45°)
- 6+ Steep (46°)
- 7+ Steep (47°)
- 8+ Steep (48°)
- 9+ Steep (49°)
Adjusting the SLZ
- The SLZ angle must match the angle of the sclera to allow the SLZ 'foot' to distribute the lens weight evenly over the scleral surface, thereby minimising the compressional footprint.
- To correct the angle of the SLZ, simply select a lens with a flatter/steeper SLZ angle.
- A steep fitting SLZ land more on the ‘toe’ of the lens, observed as conjunctival blanching at the lens edge. To correct order a flatter SLZ which will change the angle of landing, lifting the ‘toe’ and bringing down the ‘heel’ of the SLZ ‘foot’.
- A flat fitting SLZ lands more on the ‘heel’ of the lens, observed as limbal vessel blanching and scleral compression near the limbus. To correct order a steeper SLZ which will change the angle of landing, dropping the 'toe' and lifting the 'heel' of the SLZ 'foot'.
Measuring the SLZ angle using an OCT
- Cylindrical over-refraction is common with scleral lenses and is often not a result of internal or residual astigmatism; rather it can be caused by lens flexure on the eye. Nearly one in five patients exhibit lens flexure on the eye causing 0.75DC to 1.50DC of induced front surface astigmatism.
- Lens flexure is due to the scleral shape being non-rotationally symmetric. Like corneal toricity, the sclera can exhibit steep and flat meridians. The depression of the lens into the sclera occurs in the flat meridian and lens flex in the steeper meridian.
- To eliminate lens flexure, increase the lens sagittal value of the lens in the steep meridian to ensure equal weight distribution in all the meridians of the sclera. Equal weight distribution will eliminate the induced front surface astigmatism on the lens.
- To differentiate between internal astigmatism and astigmatism induced by lens flexure, perform corneal topography over the lens on the eye. Astigmatism measured on the lens front surface confirms lens flexure and provide a guideline to how much sagittal toricity is required.
- Use the following guideline table to decide how much the sagittal value in the steep meridian must be increased for an even scleral weight distribution:
- Toricity increases peripherally from the limbus. The larger the lens diameter, the more scleral toricity will be present.
- Higher degrees of scleral toricity is more typical in corneal dystrophies like Keratoconus than in normal eyes.
- To ensure no lens rotation one eye, the minimum toricity that should be ordered is 100 microns.
Step 5: Back Vertex Power (BVP)
How to order EyeSpace Scleral Toric lenses
This video tutorial will guide you through the steps necessary to order EyeSpace Scleral Toric lenses using EyeSpace software.
How to calculate the BOZR and BVP using EyeSpace and diagnostic trial lenses
Watch this video tutorial to see how to calculate the BOZR and BVP using EyeSpace software and the diagnostic trial lenses.
Order EyeSpace Scleral 2 lenses without a topography map
Watch the video tutorial on how to order EyeSpace Scleral lenses using EyeSpace software in the absence of a topography map.
EyeSpace Scleral Troubleshooting
To assist you with the EyeSpace Scleral lens fitting and troubleshooting process we have developed an EyeSpace Scleral Troubleshooting form. For more information please read the article How to fit and troubleshoot EyeSpace Scleral lenses.
Advanced Scleral Fitting Guide
For more in-depth information please read the EyeSpace Advanced Scleral Fitting Guide