Retinal structure & oxygen metabolism in highly myopic vs emmetropic eyes.

Abstract

Purpose : Recent research has investigated either retinal oxygen metabolism or structural features in highly myopic (SE>-6.00D) vs emmetropic (SE±0.50D) eyes. This research explores relationships between retinal metabolic and structural features in highly myopic (M) versus emmetropic (E) eyes.

Methods : Retinal vessel calibres (CRAE and CRVE) were calculated using 50^o fundus-images of a Zeiss FF450+ camera. For oxygen saturation parameters a dual-wavelength filter was adapted (ImedosSystems UG). Retinal nerve fibre layer (RNFL) and ganglion cell layer (GCL) thickness was derived by Zeiss Cirrus HD-OCT in 19 highly myopic (SE=-8.22(±3.06)D) and 21 emmetropic (SE=-0.10(±0.41)D) healthy participants. Other parameters assessed include intraocular pressure (IOP), systemic blood pressure, axial length and a full optometric examination. Following normality testing, group differences were analysed using t-tests. Univariate and multivariate linear regression analyses were used to evaluate structural and metabolic relationships.

Results : Both groups were comparable in age (M: 29(±10)yrs, E: 26(±9)yrs) and IOP (M: 13(±3)mmHg, E: 14(±3)mmHg). Myopes had longer axial length than emmetropes (M: 26.5(±0.7)mm, E: 23.3(±0.7)mm; p<0.001). Despite correction for ocular magnification, there were significant differences in vessel calibres (M: CRAE 144(±16)mm, CRVE 207(±23)mm; E: CRAE 170(±12)mm, CRVE 252(±19)mm; both p<0.001), venous oxygen saturation (M: 44(±11)%, E: 40(±13)%; p<0.001) and arterio-venous oxygen saturation difference (M: 45(±10)%, E: 48(±11)%; p<0.001). Other significant findings were a thinner average GCL thickness in myopes (77(±6)μm) compared to emmetropes (85(±5)μm; p=0.048), while the average RNFL thickness was comparable (p=0.782). No relationships were found for emmetropes. In contrast, myopes exhibited a relationship between nasal RNFL thickness and CRAE, arterial oxygen saturation and IOP (multiple regression: R²=0.626; p=0.002). Overall and inferior GCL thickness were related with inferior arterio-venous oxygen saturation difference (R² =0.388; p=0.004 and R² =0.395; p=0.004; respectively).

Conclusions : The relationship between structural and metabolic parameters in myopic retinas raises the question if this dependency might impact future pathology. Our findings suggest that local tissue changes may contribute to an imbalance in retinal oxygen metabolism which could lead to long term alterations in visual function.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.