Table 1.

Comparison of the Gass and IVTS group classifications

Gass stages in common use	Gass or Gass-derived classification	IVTS classification equivalent
0	VMA in the fellow eye of a patient with a known/previous IMH without any change in foveal architecture	VMA
1	Impending macular hole with outer retinal elevation from RPE at foveal center	VMT without IMH: can occur with outer or inner retinal changes or both
2	≤400 µm IMH with VMA	Small- or medium-sized IMH with VMT
3	>400 µm IMH without VMA	Large IMH without VMT
4	IMH with complete vitreous separation including from optic disk	Not classified separately could be either small, medium, or large IMH without VMT

Abbreviations: IVTS, International Vitreomacular Traction Study; VMA, vitreomacular attachment; IMH, idiopathic macular hole; VMT, vitreomacular traction; RPE, retinal pigment epithelium.