Table 3. Assessment of human sperm morphology by visual observation or computer vision (propositions for considering the advantages, limitations and usefulness of each current approach as a function of the study aims and domain for future guidelines).

Background in humans	Most of the spermatozoa leaving the testis are morphologically immature and/or abnormally shaped/sized: causes and consequences?
Approaches for assessing human sperm morphology	Stained smear Conventional microscopy Visual observation with categorization/classification			Stained smear Conventional microscopy Computer vision
Characteristics assessed	% morphologically normal sperm	and/or	% morphologically abnormal sperm in each abnormality category	Sperm morphometry
Advantages and limits of each method	Qualitative and semi-quantitative		Qualitative and semi-quantitative	Quantitative
	• Easy to use routinely • Rapid • Mainly focused on sperm head assessment • Marked inter- and intra-observer variability		• Useful for diagnosis • Useful for prognosis • Time consuming • Marked inter- and intra-observer variability	• Accuracy • Reproducibility • Facilitates etermination of subtle induced morphology changes • Correlations easily determined • Costly • Mainly dedicated to sperm head and not tail morphometry • Allows subsequent supervised visual sorting/categorization • Basic computer vision perfect for measuring, but not adapted to complex pattern recognition (cost)
	Allows integration of an informative abnormality index (MAI/SDI/TZI) Eye–brain coupling well-adapted for pattern recognition, not for measuring
Usefulness according to the application
Infertility diagnosis	++		+++	+?
ART	+++		++	+?
Reproductive toxicology	+		+	+++
Basic research	+		++	+++