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  • Title: Cone and rod ERG phototransduction parameters in retinitis pigmentosa.
    Author: Tzekov RT, Locke KG, Hood DC, Birch DG.
    Journal: Invest Ophthalmol Vis Sci; 2003 Sep; 44(9):3993-4000. PubMed ID: 12939320.
    Abstract:
    PURPOSE: To analyze cone and rod phototransduction parameters from ERG a-waves in patients with RP and to determine the relationships among these parameters, age, and mode of inheritance. METHODS: Sets of four white flashes (3.2-4.4 log scotopic troland [scot td-s]) were presented in the dark. The same stimuli were later presented against a rod-saturating background and the generated cone a-waves were subtracted from the dark-adapted responses to produce rod-only a-waves. The rod-only and cone a-waves were fit with computational models. RESULTS: Of 418 consecutive patients with retinitis pigmentosa (RP), cone a-waves were quantifiable in 136 (33%), whereas rod a-waves were quantifiable in 125 (30%). Cone R(max) (maximum response) and cone S (sensitivity) parameters were significantly below normal in all RP subgroups. Cone R(max) was lower in XlRP than in other forms of inheritance (P < 0.05). Cone S was abnormal in 77.9% of all patients with RP and in 96.8% of those with XlRP. More than 95% of the rod R(max) values were abnormal, whereas rod S was abnormal in 61.6% of these patients. CONCLUSIONS: The efficiency of cone phototransduction appears to be affected in all forms of RP, even in some patients in whom the sensitivity of rod phototransduction is normal. In this cross-sectional sample, there was no evidence that transduction efficiency decreased with increasing age of the patient. The X-linked mode of inheritance is associated with greater abnormalities in cone and rod photoreceptor function at a younger age compared with the other modes of inheritance.
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