Corneal Topography

Published on
December 4, 2023
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Corneal Topography

Integral to our Adelaide and Henley Beach practices so heavily involved with contact lenses, the topographer maps the shape of our patients' cornea – the transparent front surface of the eye. The term topography refers to capturing the shape and features of land surfaces, and just like mountains, the front surfaces of our eyes have unique topographical features. It's not only important to assess the shape of the cornea, but also to accurately assess the shape of the surrounding sclera (the white part of the eye). We're equipped with the latest in this mapping technology, investing in three distinct pieces of equipment to achieve this – the Medmont E300, the OCULUS Pentacam AXL Wave, and the Eaglet Eye: Eye Surface Profiler (ESP).

Medmont Corneal Topographer

The Medmont E300 corneal topographer uses Placido disc, or reflection-based, imaging to provide a three-dimensional representation of a patient’s cornea, with particular importance paid to thecornea.1 This information is ideal for fitting rigid gas permeable contact lenses, or RGPs. The most suitable for each patient can be selected – typically through our premier EyeSpace software. This equipment is used extensively for orthokeratology and RGP fitting in keratoconus.

Medmont software displaying anterior corneal topography of an eye undergoing orthokeratology
Figure 1. Before and after topography comparison of an eye undergoing orthokeratology, using Medmont corneal topography

Pentacam AXL Wave

The Pentacam AXL Wave tomographer uses Scheimpflug imaging to map the front and back surfaces of the cornea as well as its thickness and volume. This is a step beyond Placido disc imaging, which maps only the front corneal surface. Its accuracy as a non-contact alternative independent of tear film quality has been proven in countless clinical trials. For this reason, it’s much better for mapping eyes with dry eye disease, and in the design of various custom-made contact lenses including orthokeratology and bespoke RGP lenses. It’s also particularly useful for imaging highly irregular shaped eyes which is common in patients with keratoconus and pellucid corneal marginal degeneration, corneal graft recipients, post corneal cross-linking or in penetrating eye injuries.2, 3, 4

Pentacam AXL Wave's oculus software displaying anterior and posterior corneal topography
Figure 2. Pentacam refractive display, showing topography of the anterior and posterior cornea

Eaglet Eye ESP

The Eaglet-Eye ESP is a corneo-scleral topographer, meaning it maps out the shape of the front of the eye with incredible accuracy.5, 6 The three-dimensional maps attained by the Eaglet Eye– ESP allows our optometrists to gain a better understanding of how various corneo-scleral disease affects our patient’s eyes and vision.6

The Eaglet-Eye ESP is also very useful for designing custom-made scleral contact lenses.6 These lenses are large diameter lenses that are typically 16-18mm in diameter. Where conventional corneal topographers are limited to an8-10mm diameter scan, the Eaglet-Eye ESP gives us a much bigger picture, with the ability to capture the entire surface of an open eye! 6, 7 This means the Eaglet-Eye ESP will revolutionize the fitting of all contact lenses for anyone with lumps or bumps on their eyes, such as pinguecula or pterygiums.

Eaglet Eye Surface Profiler displaying anterior corneal and scleral topography
Figure 3. Display corneal and scleral topographic data from the Eaglet Eye Surface Profiler

References

1) Medmont International Pty Ltd. Medmont E300Corneal Topographer User Manual. Australia: Medmont Intl; 2006 Mar:4

2) Van der Worp, E. DeNaeyer, G. Caroline, P.(2017). Understanding Anterior Ocular Surface Shape. Ophthalmology: Current andFuture Developments. 4:68-87.

3) Pinero, D. Martinez-Abad, A. Soto-Negro, R.Ruiz-Fortes, P. Perez-Cambrodi, R. et al. (2019). Differences in corneo-scleraltopographic profile between healthy and keratoconus corneas. Contact lens andAnterior eye. 42(1): 75-84.

4) DeNaeyer, G. Sanders, D. (2018). CollagenCrosslinking for Keratoconus Can Change Scleral Shape. JCLRS. 2(1).

5) Iskander, R. Wachel, P. Simpson, P.Consejo, A. Jesus, D. (2016). Principles of Operation, accuracy and precisionof an Eye Surface Profiler. Ophthalmic and Physiological Optics. 36(3).

6) Iskander, R. (2013). The clinical utilityof the Eye Surface Profiler. IOVS. 54(15).

7) Ritzmann, M. Caroline, P. Borret, R.Korszen, E. (2018). An analysis of anterior scleral shape and its role in thedesign and fitting of scleral contact lenses. Contact Lens and Anterior Eye.41(2): 205-213.

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