Keratoconus with Nystagmus and Post-Intracorneal Ring Segments

This 41-year-old male has stage I bilateral keratoconus and underwent intracorneal ring segment implantation OD and OS. The resulting K readings present a flat pattern at the central cornea due to the force exerted by the ring segments. The patient also has congenital nystagmus.¹

The Rx readings are:

OD   –7.50 –3.50 x 106
OS   –11.00 –1.50 x 110

The patient first came to our clinic in 2014. He had been fit elsewhere with corneal GPs, and during the first visit he reported low-acuity vision (20/30 and 20/40, respectively), photophobia, and ocular allergy. He was previously fit with reverse geometry GPs; these lenses exhibited no movement and had no aspheric periphery to promote adequate tear exchange. This may explain the ocular irritation and photophobia. We instructed him to suspend lens wear for at least three consecutive days and then to return for a new exam.

Corneal topography revealed irregular, flat anterior sagittal curves (Figure 1). The minimum thickness was 476 microns and 471 microns, respectively, which confirmed that both corneas had a good stromal thickness and that this was stage I keratoconus.

What made this case particularly challenging was the fact that the patient also presented with significant congenital nystagmus. The examination was difficult; slit lamp observation was impractical, so we used a photo burst (or continuous shooting mode) and also took video recordings to better examine the patient. The videos also helped to evaluate the fitting (see video), especially in slow motion.

We tried 16.5mm scleral lenses, but it was difficult to apply the lenses due to the continuous side-to-side movement of his eyes. We also found that the patient had an irregular scleral shape. We opted to continue with corneal GP fitting, as this gives the patient more control during lens application. The goal was to fit lenses that would have enough mobility to promote tear exchange and enough stability to remain in place with the continuous and intense side movements of his eyes.

Management of the Case

We fit the patient with aspheric single-curve GP lenses with the following parameters:

OD: Base curve (BC) 42.50D (7.94mm), power –10.00D, overall diameter (OAD) 9.8mm, optic zone (OZ) 7.5mm, material Dk 100
OS: BC 44.00D (7.94mm), power –10.00D, OAD 9.8mm, OZ 7.5mm, material Dk 100

Note that the base curves of both lenses are much steeper compared to the average K readings. The reason for this is the flatter, plateau pattern around the central cornea created by the intracorneal ring segments. The topography beyond the area of the ring segments possibly remained similar to the pre-surgery cornea. The fit in such cases should be evaluated with trial lenses to achieve the best possible fluorescein pattern. Figure 2 shows the final GP lens fits.

The fit presented good centration, with optimal lens movement and stability. Visual acuity improved to 20/25^-2 and 20/30^-2, respectively. The patient reported good comfort with the lenses.

The ring channels are impregnated with deposits OD and OS. It does not affect the patient’s vision, but it is noticeable by others. The deposits were possibly caused by larger channels to the ring nomogram utilized, which may have been related to the instability of the eye during the dissection of the stromal channels. The patient confirmed that others notice the white deposits. He does not mind this cosmetic aspect, as it does not affect his vision.

Discussion

Fitting keratoconus is always complex, especially when fitting corneal GP lenses. In this case, the patient also underwent intracorneal ring segment implantation in both eyes. Fitting keratoconus when there are intracorneal ring segments can be more challenging, because the inferior ring segments often induce a local elevation at the end of the ring. If the lens does not vault over this small, local elevation, the friction on the corneal epithelium will induce scarring and keratitis. This causes pain as the insult to the epithelium persists, until the patient cannot tolerate lens wear.

Fortunately, this was not the case for this patient, as the elevation was not significant enough to cause abrasion. We were worried about the OS fit in which the inferior elevation at the temporal segment was greater (Figure 3), but during the subsequent follow-up visits we observed that there was no evidence of insult to the epithelium.

That being said, we had to face the additional challenge of the nystagmus condition, which makes evaluation and examination more difficult. Nystagmus has an estimated prevalence of 1 in 500,000,² and keratoconus has an estimated prevalence of 1 in 2,000³ to about 3 in 2,000⁴; to have a patient who has both conditions together is extremely rare. I found only one related case⁵ when searching for similar cases. The continuous, quick side-to-side movements make it almost impossible to achieve a good evaluation; the ability to take burst photos and video were crucial to the fitting process in this case.

References

1. Boyd K. What is Nystagmus? American Academy of Ophthalmology. Reviewed 2020 Oct 28. Available at https://www.aao.org/eye-health/diseases/what-is-nystagmus . Accessed March 1, 2021.
2. Norn MS. Congenital idiopathic nystagmus. Incidence and occupational prognosis. Acta Ophthalmol (Copenh). 1964;42(2):889-896.
3. Kennedy RH, Bourne WM, Dyer JA. A 48-year clinical and epidemiologic study of keratoconus. Am J Ophthalmol. 1986 Mar;101:267-273.
4. Kristianslund O, Hagem AM, Thorsrud A, Drolsum L. Prevalence and incidence of keratoconus in Norway: a nationwide register study. Acta Ophthalmol. 2020 Nov 16. Online ahead of print.
5. Tsang, DK, Spors F, Shen J, McNaughton LE, Egan DJ. Optical Rehabilitation of a Patient with Keratoconus and Nystagmus. Med Hypothesis Discov Innov Ophthalmol. Winter 2018;7:183-189.