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Ali S Raza, Donald C Hood; Is There a Difference in the Structure-Function Relationship between Low-Tension and High-Tension Glaucoma?. Invest. Ophthalmol. Vis. Sci. 2014;55(13):961.
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It is often thought that the nature of damage differs between low-tension (LT) and high-tension (HT) glaucoma for both structural1 and functional2 measures, though it is difficult to determine to what extent such differences (e.g., “focal” versus “diffuse” damage) reflect underlying disease physiology. Here, we compare the structure-function relationship between LT and HT glaucoma patients and suspects, as measured by standard automated perimetry (SAP) and swept-source optical coherence tomography (SSOCT).
Both 10-2 and 24-2 SAP (HFA II; Zeiss, Inc.) were obtained for 71 eyes of 71 glaucoma patients and suspects (52.5 ± 14.9 yrs; 36 HT, 35 LT) with glaucomatous optic neuropathy and a 24-2 MD better than -6 dB. SSOCT (9x12 mm widefield, DRI; Topcon, Inc.) data were also collected on this group and for 14 eyes of 14 healthy controls (54.9 ± 10.3 yrs). Total deviation (TD) values for the SAP points between 3° to 8° eccentricity in each hemifield were anti-logged and averaged, and then plotted against the average corresponding retinal ganglion cell plus inner plexiform layer (RGCP) thickness values, normalized relative to control thickness. RGCP thickness was determined by a previously-validated algorithm and the location of SAP points was corrected for ganglion cell displacement.3 The structure-function relationship was assumed to be linear for TD values ≤ 0 dB and assessed for both HT and LT by analysis of covariance (ANCOVA).
The slopes for the HT and LT linear models were not different; therefore, a reduced model with constant slope was used. The difference in the intercept for either the superior (Fig 1A; p=0.18) or inferior (Fig 1B; p=0.16) field was not statistically significant between HT and LT, though the overall relationship between RGCP and SAP was statistically significant (p<0.01) for both hemifields.
Though the HT individuals exhibited a slightly greater structural loss per unit of functional loss than the LT individuals, there is no significant difference in the structure-function relationship. Thus, further work is necessary to better understand previously reported differences between HT and LT glaucoma. 1Yamazaki Y et al. Graefe’s. 1991. 2Chauhan BC & Drance SM. IOVS. 1990. 3Raza et al. AO. 2011.
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