New EyeSpace Features - Scleral order module

September 30, 2018Charl Laas

In our final instalment on new EyeSpace features, I will look at the EyeSpace Scleral order module. One of the main advantages of EyeSpace Scleral lenses is the ability to easily customise the lens design to ensure an individualised lens-to-eye fitting relationship.

The EyeSpace Scleral design page is divided into four sections, each aiding you to customise the scleral lens design further.

1. Lens design

Use the drop-down box to choose a rotationally symmetric, toric or quadrant-specific design.

2. Basic Lens parameters

Depending on the lens design chosen, the left panel displays the different meridians of the lens requiring design input. On the right panel of the page, with the 'Lens Schematic' tab selected, EyeSpace presents a line schematic of the lens designed.

Rotationally symmetric (spherical) design

Toric design

Quad design

Back Optic Zone Radius (BOZR)

EyeSpace selects the Back Optic Zone Radius (BOZR) based on the best fit sphere (BFS) value from the captured topography map. On the right side of the page, select the 'Optic Zone Tear Film Thickness' tab to display the tear film thickness (TFT) profile between the Back Optic Zone and the cornea. Should the clinical findings show a different BOZR is required the value can be overridden and the new TFT profile will be displayed on the right.

Sagittal Height at 15.00 mm chord (Sag@15mm)

Enter the desired sag values for the principal meridians. The sag values are determined in conjunction with using the EyeSpace Scleral diagnostic lenses. For more information read the EyeSpace Scleral 2 quick start guide.

Scleral Landing Zone (SLZ)

The SLZ angle must match the angle of the sclera to allow the SLZ 'foot' to distribute the lens pressure evenly over the scleral surface, thereby minimising the compressional footprint.

Each meridian SLZ angle can be independently adjusted using the following parameters:

  • 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°)

Diameter

The EyeSpace Scleral 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.

3. Advanced Parameters

Activate the Show Advanced Parameters checkbox to modify the Back Optic Zone Diameter (BOZD).

The BOZD can be ordered in various diameters ranging from 6.00 mm to 9.00 mm, with the default value set at 8.00 mm.

Why is it important to adjust the BOZD? To answer this, consider the following: To reduce the risk of clinically significant oedema with scleral lenses, current research suggests having a uniform post-lens tear thickness (PLTT) of less than 200 microns over the central cornea and 50-60 microns at the periphery.

Imagine fitting nipple keratoconus which presents as a small, near central cone with a diameter of 5.00 mm or less. Typically, fitting a scleral lens with a large BOZD on a small diameter nipple cone results in an increasing amount of entrapped tears towards the cornea's mid-periphery due to the misalignment of the peripheral optic zone and the contour of the cornea. As with corneal GP lenses, reducing the BOZD minimises the misalignment and reduces the subsequent tear pooling around the base of the cone. Decreasing the mid-peripheral tear pooling, allowing for a more uniform post-lens tear thickness, not only helps to improve oxygenation of the corneabut might also help to reduce the negative hydrostatic or suction pressure under the lens. In the author's opinion reducing the tear volume in the mid-peripheral area will in turn also aid to minimise the occurrence of limbal congestion.

Decrease the EyeSpace Scleral BOZD to reduce mid-peripheral tear pooling when fitting nipple keratoconus

Consider another example of fitting scleral lenses on penetrating keratoplasties with graft button seizes larger than 8.00 mm. Usually, to avoid mid-peripheral lens touch on the graft margin the sagittal height of the scleral lens has to increase resulting in an undesirably high central post-lens tear film thickness. By increasing the BOZD to match the graft button size, the mid-peripheral lens section - junction point where the BOZ meets the Z-Zone - can successful vault the graft button and so eliminate the need to increase the overall sagittal height of the scleral lens.

Increase the EyeSpace Scleral BOZD to vault the graft margin of large button Penetrating Keratoplasties

4. Back Vertex Power

Finally, enter the BVP of the EyeSpace Scleral lens.

Video

The video below provides a step by step guide on how to order a pair of EyeSpace Scleral Toric lenses using the EyeSpace Scleral order module.

https://vimeo.com/271613168

References

Vicente C. Oxygen Diffusion and Edema With Modern Scleral Rigid Gas Permeable Contact Lenses. _Investigative Ophthalmology & Visual Science. _October 2014, Vol.55, 6421-6429.

Jaynes JM, Edrington TB, Weissman BA. Predicting scleral GP lens entrapped tear layer oxygen tensions. Contact Lens and Anterior Eye. 2015 Jan 31;38(1):44–7.

Michaud L, van der Worp E, Brazeau D, Warde R, Giasson CJ. Predicting estimates of oxygen transmissibility for scleral lenses. Contact Lens and Anterior Eye. 2012 Nov 30;35(6):266–71.

Munsamy A. A correlation analysis of cone characteristics and central keratometric readings for the different stages of keratoconus. Indian Journal of Opthalmology. 2017 Jan;65(1):7–11.

Rose P. A systematic approach to fitting keratoconus lenses. Canada: Contact Lens Society of America. 2005.

Correction of Keratoconus with GP Lenses. Centre for contact lens research, School of Optometry at the University of Waterloo, Canada. Accessed August 2018, https://www.artoptical.com/storage/docs/Correction_of_Keratoconus_with_GP.pdf.

Rose P. Improving a Keratoconus Lens Design. Contact Lens Spectrum. June 1, 2005, accessed August 2018, https://www.clspectrum.com/issues/2005/june-2005/improving-a-keratoconus-lens-design.

Compañ V, Aguilella-Arzo M, Edrington TB, Weissman BA. Modeling Corneal Oxygen with Scleral Gas Permeable Lens Wear. Optom Vis Sci. 2016;93(11):1339-1348.

Jaynes JM, Edrington TB, Weissman BA. Predicting scleral GP lens entrapped tear layer oxygen tensions. Cont Lens Anterior Eye. 2015;38(1):44-47.

Allaire PE, Flack RD. Squeeze forces in contact lenses with a steep base curve radius. Am J Optom Physiol Opt. 1980;57(4):219-227.