A study recently published in Investigational Ophthalmology & Visual Science investigated associations between multiple visual factors and Fuchs endothelial corneal dystrophy (FECD).
Give me some background first.
FECD is a bilateral disorder that frequently leads to:
- Abnormal deposition of the extracellular matrix
- Thickening of the Descemet's membrane
- Progressive loss of corneal endothelial cells leading to corneal edema and vision impairment
Some successful treatments have included:
- Descemet membrane endothelial keratoplasty (DMEK)
- Descemetorhexis without endothelial keratoplasty (DWEK)
Go on…
The authors noted that “some patients with FECD report visual disturbances, despite the absence of corneal edema.” FECD without corneal edema is associated with:
- Higher-order aberrations (HOAs)
- Intraocular forward light scatter (straylight)
Notably: It was “assumed that the corneal guttae increase straylight, which causes visual disturbance.”
What was the objective of this study?
The researchers in this study aimed to evaluate the associations between FECD and different levels of visual function, HOAs, and scatter.
Who was included in the study?
This was an observational case series study that included 27 patients (49 eyes) with FECD and 10 patients (10 eyes) that were healthy for control.
Patients were recruited from the outpatient clinic of the Department of Ophthalmology at Osaka University Hospital. The study was conducted from January 15, 2019 to October 2, 2020.
Talk about the outcome measures.
Visual function was assessed from the following measures:
- Corrected distance visual acuity (CDVA)
- Contrast sensitivity
Explanatory parameters included:
- Age
- Modified Krachmer grade
- A 0 to 6 severity grading system for FECD where a grade of 0 = no guttae and grade 6 = over 5 mm of confluent central/paracentral guttae with clinically apparent stromal and/or epithelial edema.
- Central corneal thickness (CCT)
- Anterior segment optical coherence tomography (AS-OCT)-based grade
- HOAs
- Intraocular straylight (representing forward light scatter)
- Corneal densitometry (representing backward light scatter)
Statistical analysis was then conducted to determine associations.
Findings?
Visual function was found to be associated with:
- Modified Krachmer grade
- CCT
- Anterior segment OCT-based grade
- HOAs
- Intraocular straylight
- Corneal densitometry
Note: Modified Krachmer grade 3 occurs when “corneal guttae become confluent.”
- Thus: A Krachmer grade of ≥3 was identified as the decreased vision function threshold.
Go on…
In addition, the group of those with a modified Krachmer grade of ≥3, those with 0 mm to 2 mm of central corneal densitometry values of the posterior layer ≥10 GSU had decreased CDVA.
Expert opinion?
Per the authors of the study: “This might suggest that corneal densitometry would be more valuable than the modified Krachmer grade to determine patients with significantly decreased visual function.
They continued: “Therefore, we believe that corneal backward light scatter is the most influential factor affecting visual function.”
Anything else?
Participants with an AS-OCT-based grade 1 had significantly impaired visual function. This grade included participants with modified Krachmer grades of 2, 3, and 4.
The researchers suggest: “AS-OCT-based grading appears not to be particularly sensitive for the evaluation of visual dysfunction.”
Limitations?
The study authors noted that the sample size was relatively small, and that a larger one will be necessary to fully determine which of the variables in this study was the most relevant.
Take home.
While future studies are needed to continue this research, this study identified parameters for a threshold for significant vision impairment in patients with FECD.