DIGITAL PATHOLOGY
filter out minor imperfections such as debris, staining variability, or refractive inconsistencies.2
Slide defects rarely
compromised diagnostic accuracy, as the human brain reconstructs context and selectively ignores artefacts. Today, however, glass slides and coverslips represent the gateway between the physical specimen and the evolving digital ecosystem.
As pathology workflows transition
from analogue to digital, glass slides and coverslips assume a new role: they become critical optical and data- generating components of complex imaging systems. Whole slide scanners convert optical signals into massive datasets, often exceeding several gigabytes per slide. These images are then interpreted by pathologists and by computational systems that lack the mental filtering capabilities of the human brain. It becomes more apparent that the quality, consistency, and performance of these glass components directly influence image resolution and clarity, colour reproducibility, scan speed and throughput, file size and storage burden, and algorithmic training and performance. Slides no longer merely support tissue, they play an active role in diagnostic outcomes. Glass slides and coverslips now need to be engineered with digital compatibility in mind.
Why material quality matters Glass used in microscopy must meet stringent optical requirements. These include optical clarity, uniform thickness, minimal impurities, and consistent refractive index. Deviations in these properties often introduce distortions that degrade image quality. In digital systems, these can result in blurs, chromatic distortion, and contrast variations that all can impact analysis. Not all glass is created equal. Clarity, chips, and debris in glass can be affected by the manufacturing process. European low-iron float glass offers superior clarity and dimensional uniformity. During the manufacturing process, molten glass floats horizontally over tin as it dries, producing a smooth, uniform sheet with minimal stress. This greatly reduces surface defects, contamination, and thickness variability. In contrast, vertically drawn or
mechanically rolled glass, common in lower-cost slide manufacturing, allows the molten glass to cool as it is suspended vertically, causing strain, uneven dimensions, and routine contamination. This may not be as visible under manual microscopy but is readily detected by high-resolution scanners.
Cover glass Cover glass is the first optical element that light encounters when capturing
images. The quality of cover glass may also be crucial in maintaining optical clarity, allowing light to pass through without distortion. Factors such as glass composition, thickness, refractive index, and Abbe value (true to life colour representation) also play a role in how accurately light passes through and is interpreted by digital scanners. Poor quality cover glass may introduce subtle distortions that can alter optical performance in digital images: autofocus failures, increased rescanning rates, and degraded image uniformity. Borosilicate cover glass uses high-
quality ingredients and a down-drawn production process creating a smooth, uniform surface with a higher refractive index, allowing light to pass through for beter imaging. Soda lime cover glass is stretched in
manufacturing, allowing for uneven glass, distortion, and a lower refractive index, affecting image clarity.3 Over millions of slides annually, even
small inefficiencies add up to substantial operational and financial burdens.
Hidden variables in digital workflows Digital pathology is a highly sensitive application, where even subtle factors can significantly impact image quality long before scanning begins. Preanalytical variables include: Fixation quality Tissue processing Paraffin infiltration and embedding Microtomy Section thickness consistency Slide adhesion Staining quality.
Each step introduces potential sources of variability that compound as slides progress through the laboratory workflow. Common artefacts like tears, folds, chater, contamination, section thickness, or uneven staining, are often tolerated in conventional microscopy. In digital pathology these imperfections generate image noise, especially if the area of concern is in one of these imperfections. These seemingly minor flaws can compromise not only visual clarity, but also the performance of trained AI algorithms.
Even seemingly minor flaws can compromise not only visual clarity, but also the performance of trained AI algorithms.
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WWW.PATHOLOGYINPRACTICE.COM June 2026
Background staining While atention is often given to image clarity and scanner performance, non-specific background staining can significantly affect the efficiency and economics of digital scanning systems. A study carried out by StatLab Medical Products assessed how background staining affects scan time and file size
AdobeStock / AnnaStills
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