FAAO FBCLA FSLS FIAO
Director technical affairs, Precision Technology, Vancouver, Canada
Medmont E300 USB Corneal Topographer
In contact lens practice, diseased, post-surgical and asymmetric eyes present some of the most challenging cases that test our expertise and skill. It’s often simply time or the lack of it that impedes an efficient and successful outcome.
The corneal topographer aids in choosing the correct initial diagnostic lens for these patients and can also assist in predicting the final custom lens parameters required. Choosing the wrong initial diagnostic lens is certain to prolong the discomfort of the patient.
Figure 1 shows a scleral diagnostic lens with totally inadequate apical clearance. This lens needs to be removed and another higher depth trial lens should be applied.
Figure 1. Scleral diagnostic lens with inadequate apical clearance
Diagnostic imaging software
Using the ‘composite eye’ capture feature (Medmont E300 Corneal Topographer) allows the practitioner to estimate the height of the anterior chamber with great accuracy.1 This improves the efficiency of the diagnostic process as practitioners are more likely to choose the correct diagnostic lens the first time rather than place multiple trial lenses on the eye of the patient before the correct lens is found (Figure 2).
Figure 2. The optimal diagnostic pattern
Choosing the correct initial diagnostic is only half the battle. In many cases, scleral lenses may require some customisation to achieve an optimal outcome. The Medmont software has unique features that provide insight to the practitioner prior to the lens being placed on eye.
After choosing the KATT/ICD 16.5 mm scleral design from the contact lens software, a theoretical fluorescein pattern is created. The user can observe the apical clearance, limbal vault and scleral landing through the tear layer profile graph (Figure 3).
Figure 3. The tear layer profile graph displaying a scleral lens prior to settling
Then a ‘settling factor’ can be applied to sink the lens into the soft conjunctival tissue just as an actual scleral lens would on the eye. Numerous studies have shown the KATT/ICD 16.5 mm sinks approximately 125 microns during wear.2
The user can model this compression of the conjunctiva tissue by entering a settling depth to observe changes to the apical and limbal clearance as well as the landing (Figure 4). Likely modifications to the specific zones of the lens can be predicted before the lens is placed on eye (Figure 5).
Figure 4. This image shows the tear layer profile after the scleral lens has been ‘settled’ into the conjunctiva and resulting limbal bearing
Figure 5. The Limbal Clearance Zone is altered to ensure the appropriate limbal vault post settling
The Medmont E300 contact lens module is an accurate tool for the design of corneal GP lenses3 but its accuracy is not limited to diameters that fall within the limbus.4 This instrument can also be employed to improve the efficiency of scleral lens practice.5 Allow this instrument to predict the initial diagnostic lens but also have it guide adjustments to the various zones to save on remakes and reduce chair time.
1. Harkness B. Comparison of Sagittal Height Measurement Methods. New Orleans, LA: American Academy of Optometry; 2015.
2. Caroline P, André M. Scleral lens settling. Contact Lens Spectrum 2012; 27: 56.
3. Sindt CW, Grout TK, Kojima R. Evaluating virtual fitting for keratoconus. CL Spectrum 2011; 21: 39-43.
4. Hall L, Young G, Wolffsohn J, Riley C. The influence of corneoscleral topography on soft contact lens fit. Invest Ophthal Vis Sci 2011; 52: 9: 6801.
5. Kojima R et al. Eye Shape and scleral lenses. Contact Lens Spectrum 2013; 28: 38-43.