Clinical science Optical coherence tomography (OCT) parameters of the three different types of lamellar macular Table 1 defects Types of lamellar macular defect MPH (n = 39) (SD) LMH (n = 26) (SD) FP (n = 27) (SD) F and p Value* Initial VA (logMAR) 0.10 (0.15){{ Base diameter (mm) 452 (178){{ Defect depth (mm) 182 (54){{ Central foveal thickness (mm) 141 (26){ Perifoveal thickness (mm) 322 (54){ 0.28 (0.25) 1022 (632)1 216 (54)1 122 (36) 338 (57){ 0.30 (0.26) 707 (377) 144 (47) 104 (34) 281 (22) F2,89 = 8.272, p = 0.001 F2,89 = 15.184, p,0.0001 F2,89 = 12.757, p,0.0001 F2,89 = 10.747, p,0.0001 F2,89 = 10.488, p,0.0001 *One-way analysis of variance. {Statistical significance between MPH and LMH, post-hoc Bonferroni analysis, p,0.05. {Statistical significance between MPH and FP, post-hoc Bonferroni analysis, p,0.05. 1Statistical significance between LMH and FP, post-hoc Bonferroni analysis, p,0.05. FP, foveal pseudocyst; LMH, lamellar macular hole; MPH, macular pseudohole; VA, visual acuity. Incorporating OCT imaging as part of the routine investigation for macular disorders not only makes differential diagnosis easier, but provides qualitative assessment and allows visualisa- tion and classification of the different subtypes of lamellar macular defects, as well as quantitatively characterising the defects by providing objective measures such as base diameter and depth. OCT is also effective in evaluating the vitreoretinal interface to detect epiretinal membranes that are frequently associated with lamellar macular defects and implicated as a contributing factor in their formation.13 Figure 3 (A) Number of eyes with or without epiretinal membrane (ERM) based on the depth of lamellar macular defect, expressed as a percentage of normal perifoveal retinal thickness. As the depth of the lamellar macular defect increased, the number of eyes with ERM increased. For depth over 33% of retinal involvement, over 60% of defects had associated ERM. (B) Number of vitrecomised and non- vitrecomised eyes based on the depth of lamellar macular defect, expressed as a percentage of normal perifoveal retinal thickness. The majority of shallower defects (over 80%) did not undergo a vitrectomy, while close to half of lamellar defects with more than 67% of retinal thickness involvement underwent a vitrectomy. Br J Ophthalmol 2008;92:1342–1346. doi:10.1136/bjo.2007.133041 We have attempted in this study to provide correlations between OCT morphology of lamellar macular defects and visual function, which, to the best of our knowledge, has not been reported previously for lamellar holes. Among the different subtypes, we found that lamellar defects with a sharply punched out profile corresponding to MPH had the best level of acuity compared with that of LMH and FP. Morphologically on OCT scans, MPH had the smallest base diameter and thickest central foveal tissue, while LMH had the widest and deepest defects, and FP had the thinnest measured central foveal thickness. Our findings are consistent with the findings of Haouchine et al14 where MPH was found to be of a smaller diameter than that of LMH. The measured central foveal thickness in MPH (141 (26) mm) in our study was also comparable with the findings of Haouchine et al14 (167 (42) mm) and falls within the range of the normative data for central foveal thickness found by Massin et al (146 (20) mm).20 While the findings are consistent, there was one distinct difference between our study and that of Haouchine et al14 where we measured the widest intraretinal split as the base diameter rather than the opening of LMH. This in our opinion has allowed greater discrimination between the different subtypes of lamellar defects, as the opening diameter of LMH measured in our study was not significantly different from that of MPH. In addition, the characteristic lateral split between the inner and retinal layers has been suggested to be the result of the separation between the outer plexiform layer and the outer nuclear layer (ONL) or, more specifically, between Henle fibres and ONL.21 22 If the photoreceptor axons are separated from the inner retina, then it could be suggested as one of the underlying causes of reduced vision in lamellar macular defects, in addition to the partial loss of foveal tissue. Measuring the intraretinal cleft therefore may correspond better to the reduction in vision and provide better differentiation from lamellar defects without the characteristic lateral split such as in MPH. In full-thickness macular holes, the associated visual loss is said to result from the direct loss of foveal tissue, and there is a suggestion that the thickness of cellular tissue between the base of the hole and the RPE layer is inversely proportional to the patient’s resulting VA.1 23 It is thus reasonable to draw tentative conclusions from our findings that the higher level of acuity of MPH was attributable to the smaller diameter and thicker central foveal tissue, while the poor acuity of LMH and FP was due to the deeper/wider intraretinal split and thin foveal tissue respectively. Throughout the manuscript, we have described MPH, LMH and FP under the same banner of lamellar macular defects, as they are all partial-thickness macular holes with preservation of some foveal tissue. They also all meet the OCT criteria of lamellar holes devised by Witkin et al,13 having an irregular 1345