Corneal Topography

Integral to our Adelaide and Woodville practices so heavily involved with contact lenses, the topographer maps the corneal shape of our patients' eyes. The term topography refers to capturing the shape and features of land surfaces, and just like mountains, the front surface 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 Eaglet Eye: Eye Surface Profiler (ESP) and the OCULUS Pentacam AXL Wave.


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 what most topographers use (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.3, 4, 5

Figure 1: Various refractive maps of a keratoconic eye as taken by the Pentacam AXL Wave.

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.1, 2. 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.4

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 an 8-10mm diameter scan, the Eaglet-Eye ESP gives us a much bigger picture, with the ability to capture the entire surface of an open eye! 2, 6 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.

Medmont Corneal Topographer

The Medmont E300 corneal topographer provides a similar three-dimensional representation of a patient’s cornea, with particular importance paid to the cornea.7 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.


References
  1. Iskander, R. Wachel, P. Simpson, P. Consejo, A. Jesus, D. (2016). Principles of Operation, accuracy and precision of an Eye Surface Profiler. Ophthalmic and Physiological Optics. 36(3).
  2. Iskander, R. (2013). The clinical utility of the Eye Surface Profiler. IOVS. 54(15).
  3. Van der Worp, E. DeNaeyer, G. Caroline, P. (2017). Understanding Anterior Ocular Surface Shape. Ophthalmology: Current and Future Developments. 4:68-87.
  4. DeNaeyer, G. Sanders, D. (2018). Collagen Crosslinking for Keratoconus Can Change Scleral Shape. JCLRS. 2(1).
  5. Pinero, D. Martinez-Abad, A. Soto-Negro, R. Ruiz-Fortes, P. Perez-Cambrodi, R. et al. (2019). Differences in corneo-scleral topographic profile between healthy and keratoconus corneas. Contact lens and Anterior eye. 42(1): 75-84.
  6. Ritzmann, M. Caroline, P. Borret, R. Korszen, E. (2018). An analysis of anterior scleral shape and its role in the design and fitting of scleral contact lenses. Contact Lens and Anterior Eye. 41(2): 205-213.
  7. Medmont International Pty Ltd. Medmont E300 Corneal Topographer User Manual. Australia: Medmont Intl; 2006 Mar:4