Innovative Corneal Imaging Device

Prototype shows rich potential of high-resolution aberrometry.

DERMOT MCGRATH REPORTS

Anovel high-resolution device capable of performing reliable, precise measurements of ocular aberrations could potentially lead to new screening or follow-up methods for patients with keratoconus or other corneal diseases, according to Mr Gonzalo Velarde-Rodríguez.

“The ocular aberrations measured by this device are reliable, precise, and well correlated with the corneal aberrations. Furthermore, the extraordinary high-resolution measurements revealed micro-alterations in the wavefront phase of keratoconus patients that varied with the disease stage,” he said.

Typically, keratoconus cases are detected in clinical practice using the slit lamp or classified using topography or aberrometry devices, usually based on Hartmann-Shack technology.

However, these approaches have limitations, with Hartmann-Shack devices, for instance, restricted to sampling the phase map at up to 2,600 measurement points within the pupil, or approximately 175 µm of lateral resolution for a 9-mm pupil diameter. This constrains its usefulness in abnormal eyes, which are precisely the most interesting to characterise, he noted.

The aberrometer prototype (t-eyede, Wooptix) was developed originally for the astrophysics field with sensors capable of detecting propagating light waves. The wavefront phase imaging (WFPI) sensor allows the user to acquire millions of data points within the pupil of the human eye with a lateral resolution of 8.55 µm, which is several orders of magnitude higher than current industry standard ophthalmic devices.

Mr Velarde-Rodríguez’s cross-sectional study included 43 eyes from 25 healthy patients and 43 from 27 keratoconus patients analysed by a corneal tomography system and the aberrometer prototype. Corneal aberration values were provided by the tomography device and compared with ocular aberration scores obtained from intensity images captured by the t-eyede device.

“We wanted to use the prototype to measure real patients, including healthy and highly aberrated eyes, and to compare the corneal and ocular optical aberrations,” he said. “We also set out to study the small details of the ocular wavefront because of the huge lateral resolution of this device.”

The results showed all ocular and corneal optical aberrations were statistically significantly higher in the keratoconus group than in the control group.

“As we expected, keratoconus and healthy eyes were different. Keratoconus eyes have higher amounts of coma but also higher amounts of astigmatism and higher-order aberrations. The ocular and corneal aberrations were also different for keratoconus eyes, especially for astigmatism and coma,” he said.

Analysing the ocular wavefront using the high pass filter map helped obtain the two main patterns.

“The first pattern we identified as ‘smooth,’ with around 95% of the healthy eyes belonging to that group,” Mr Velarde-Rodríguez explained. “However, we found another pattern that we call ‘rough’, and 77% of the keratoconus eyes belonged to that group. It also seems like the disease severity played a role in the resulting pattern, as more advanced stage 3 and 4 keratoconus eyes were more likely to show this rough pattern.”

The study did have some limitations, he added.

“We made the analysis using a 3-mm pupil because the larger pupils are prone to fail,” he said. “Also, the wavefront micro-alterations are detected in the ocular wavefront, and we cannot distinguish between corneal and lens contributions in those alterations.”