Endothelium and SiH lens fitting considerations

Pauline Xu

Pauline graduated in 2007 with a Bachelor of Optometry degree (First Class Hons) from the University of New South Wales. She worked as a teaching assistant in a range of optometric courses during her studies. She published two papers from her research when a student: Mechanism for corneal reshaping in hyperopic orthokeratology (2009), Domestic water quality and contact lens-related microbial keratitis (2007)

After graduation she worked in a variety of optometric practices in regional and metropolitan locations around Australia. She joined the Brien Holden Vision Institute in 2010 as a research optometrist. 

Fuchs’ dystrophy is an inherited corneal disorder that stems from primary malfunction of the corneal endothelium. A compromised endothelial pump mechanism results in corneal swelling. Patients typically awaken with blurry vision due to increased swelling of cornea overnight, which gradually improves during the day. In more advanced cases, epithelial edema reduces visual acuity, causes pain and induces photophobia.

Fuchs’ dystrophy is characterized by accumulation of focal refractive excrescences called guttata at the posterior corneal layer (Figure 1). 

Figure 1: Prominent endothelial guttata

Other biomicroscopic findings would include stromal edema, folds in Descemet’s membrane and, at a later stage, epithelial microcysts and bullae.  Medical treatments aim to reduce edema by hypertonic saline/ointments and/or blowing warm air across the cornea with, for example, a hairdryer.  Surgical intervention, in the form of a penetrating keratoplasty, is indicated if vision deteriorates to a disabling level.
 
Fitting contact lenses for patients with Fuchs’ dystrophy is particularly challenging as the cornea is physiologically and optically compromised.  Traditional hydrogel contact lenses with low oxygen transmissibility (Dk/t) are highly problematic as the resultant lens-induced hypoxia can produce further corneal swelling and exacerbate symptoms.

In order to maximise patient comfort and vision, high oxygen permeability (Dk) silicone hydrogel lenses are the preferred choice.  

A 28 year old female presented for a routine assessment and indicated interest in contact lens wear.

Her refractive results and visual acuity are shown in Table 1.

Table 1: Presenting refractive error and visual acuity

General health and medical history was unremarkable.

Family ocular history revealed that her mother was diagnosed with Fuchs’ dystrophy in her early 40s and subsequently underwent a penetrating keratoplasty in the right eye at the age of 55.

Slit lamp examination revealed an essentially normal ocular appearance except for the endothelial cell layer in each eye.

High magnification examination of the endothelium (Figure 2) showed signs polymegethism, uneven cell layer surface and Blebs (see arrows in Figure 2)

Figure 2: Endothelial cell layer appearances

Corneal thickness was measured 11.30 am using an optical pachometer. The results indicate that the corneas are slightly thicker: OD 603 and OS 619 microns

As this was the first measurement of corneal thickness for this patient, we cannot say whether the cornea is simply slightly thicker than normal or oedematous due to altered endothelial function. A measurement of the diurnal variation in corneal thickness would be of interest in cases such as this one.

A discussion about the patient’s endothelial condition and potential progression because of the genetic link did not dull her enthusiasm for trialling contact lenses. In this case the best soft contact lens option for her was silicone hydrogel, as these lenses provide maximum oxygen to the cornea for maintaining its health.

Both eyes were fitted with Biofinity (Comfilcon A, CooperVision) lenses (Table 3):

Table 3: Prescribed contact lenses

Lens fitting characteristics were ideal and the initial comfort level was good. The patient was instructed to limit wearing time to a maximum of 10 hours per day. Her report at subsequent visits indicated that she was very satisfied with the lens performance and the level of vision achieved.

Follow-up of this case over a two month period did not indicate any detrimental effects of lens wear on the endothelium. Corneal thickness measurements remained at the baseline levels.

In this case, selection of silicone hydrogel lenses with very high oxygen transmission (Dk/t) was dictated by the physiological challenge to the cornea. Endothelial cell function is sub-optimal both in the short and long term due to presence and potential development of Fuchs’ dystrophy.  Silicone hydrogel lenses are more likely to maintain the corneal integrity comparing to hydrogel lenses.  Strict compliance with wearing regiment and regular quarterly aftercare is also essential for the patient to achieve successful contact lens wear into the future.

Longer term follow-up will include the following assessment plan:

• Monitoring the endothelium preferably with a confocal or specular microscope.
• Early detection of stromal edema such as striae and folds
• Measuring corneal thickness
• Corneal topography measurements