Abstract:  Objective  To observe changes of the macular fovea thickness in outer retina layer by layer in patients with cone dystrophy (CD) and cone-rod dystrophy (CRD) at different stages. Design  Retrospective case series. Participants 14 cases (28 eyes) CD, 21 cases (42 eyes) CRD diagnosed clinically and 19 cases (38 eyes) normal control. Methods  Extent of the outer retina damage of all eyes was categorized into 4 grades (G1~G4) based on the extent of damaged layers in the outer retina by optical coherence tomography (OCT). OCT was adopted to measure the macular fovea thickness layer by layer. Layered changes of the macular fovea thickness were observed and compared with normal control in patients with CD and CRD at different stages, included central macular thickness (CMT), outer retina (OR), outer nuclear layer (ONL), myoid zone (MZ), ellipsoid zone (EZ), outer segment (OS), interdigitation zone (IZ), and RPE/Bruch membrane complex (RBC). Main Outcome Measures  The thickness of CMT, OR, ONL, MZ, EZ, OS, IZ and RBC in G1~G4. Results  The EZ (12.76±1.15) μm and IZ (16.80±1.38) μm of G1 eyes were thinner than EZ (13.80±0.99) μm and IZ （19.41±1.60) μm of the control group (all P<0.001). There was no significant difference between CMT, OR, ONL, MZ, OS, RBC and those of the control group (all P>0.05). The OR (96.72±5.82) μm, EZ (12.37±0.61) μm, IZ (15.44±2.21) μm and RBC (15.97±1.42) μm of G2 eyes were thinner than OR (105.62±3.56) μm, EZ, IZ and RBC (17.68±1.39) μm of the control group (all P<0.001). There was no significant difference between CMT, ONL, MZ, OS and those of the control group (all P>0.05). The CMT (191.26±25.51) μm, OR (80.61±8.40) μm and MZ (22.81±2.34) μm of G3 eyes were thinner than CMT (210.46±13.07) μm, OR and MZ (27.57±2.60) μm of the control group (all P<0.001). The EZ, IZ, OS and RBC were severely damaged and could not be measured layer by layer. The CMT (112.56±41.11) μm, OR (56.48±22.88) μm and ONL (56.08±21.54) μm of G4 were thinner than those of the control group (all P<0.001). MZ, EZ, OS, IZ and RBC could not be measured layer by layer. CD patients (14 cases, 28 eyes) were G1, CRD patients (21 cases, 42 eyes) were G2~4. Conclusion Layered measurement of the macular fovea thickness in outer retina can provide a basis for grading the extent of damage at different stages. thinned EZ and IZ may occur in early CD. 

Key words: Optical coherence tomography, Electroretinogram, Central macular thickness, Cone dystrophy, Cone-rod dystrophy