A recent study published in BMC Ophthalmology evaluated the associations between corneal topography, visual function, and pterygiums.
Give me some background first.
A pterygium is known to cause changes to the structure and function of the ocular surface. However, no data exists showcasing how pterygium impacts visual function in low light.
Thus, researchers set out to evaluate the specific effects of pterygium on the topography of the cornea, as well as the refractive changes it causes in natural-light and low-light conditions.
Now, talk about the study.
This retrospective cohort study consisted of 60 participants diagnosed with primary unilateral pterygium from January 2021 to August 2021.
The study’s control was the eye of the same subjects that did not have pterygium. Demographics of the participants were also recorded, and other ocular diseases and surgeries were used as exclusion criteria.
How was the study conducted?
Each participant underwent a comprehensive ophthalmic exam that included topography and slit-lamp photography (to assess pterygium severity).
The Sirius Scheimpflug Analyzer (CSO, Costruzione Strumenti Oftalmici) is a new imaging device that was used to measure pupil size, and to quantify corneal astigmatism and aberrations.
What were the outcome measures?
At pupil diameter levels of 3 mm and 7 mm the following was recorded:
- Uncorrected visual acuity (UCVA)
- Best-spectacle-corrected visual acuity (BSCVA)
- Corneal topographic aberration data
These diameter levels were chosen to simulate natural light illumination and low-light conditions respectively.
Go on…
In addition, the following was recorded in relation to pterygium and the cornea:
- The size of the pterygium
- Horizontal length (HL) was measured as distance from nasal limbus to the pterygium's apex
- Vertical length (VL) represented distance between two limbal points where pterygium intersected with limbus
Findings?
BSCVA values were similar between the pterygium and control groups. For UCVA values, the pterygium group was significantly lower.
In addition, for the front corneal surface, pterygium was associated with a decrease in corneal power and an increase in corneal astigmatism.
And in the back?
At the 3mm area in the back corneal surface, the pterygium and control groups did not have statistically significant differences in corneal power or astigmatism.
Now talk about low-light conditions.
The parameter of 7mm simulated low-light conditions. Compared to the 3mm area, the astigmatism, total aberrations and higher-order aberrations were all larger in eyes with pterygium.
The researchers suggested that this showcased worse visual function in low-light conditions in the participant population.
Expert opinion?
Per the study authors, “The pterygium impaired visual function by inducing focal corneal flattening, severe astigmatism and increased corneal aberrations, not just by invading the visual axis or distorting the central topography.”
Take home.
This study offered new insights into low-light conditions and pterygium, and novel findings about the visual function effects.
The researchers suggested, “Patients with pterygium had poor visual function in low-light conditions. Those who worked in relatively dim environments should be advised to undergo surgery earlier.”