**2.6 Leber hereditary optic neuropathy**

Leber hereditary optic neuropathy (LHON) is the most common inherited mitochondrial disorder and typically affects young males. It typically begins as a unilateral progressive optic neuropathy with sequential involvement of the fellow eye months to years later. Fundus examination may initially reveal normal or pseudo-edematous optic nerves and telangiectatic peripapillary vessels (**Figure 21**) [25]. In late phases, the affected optic disc becomes pale and atrophic. Peripapillary OCT shows axonal swelling, which occurs during the acute phase of the disease (**Figure 22**). Furthermore, OCT clearly detects atrophy of the RNFL following the acute event [26]. In some asymptomatic eyes, OCT may demonstrate an increased RNFL thickness of the temporal quadrant (papillo-macular bundle). In FA of acute involved optic nerve head, no leakage is detected. OCTA may reveal peripapillary telangiectasia in acute phase, followed by capillary dropout, especially in the papillo-macular bundle and also disc cupping (**Figure 23**) [27].

**Figure 20.** *FA of the same patient with lead poisoning: both discs have leakage, suggestive of bilateral disc swelling.*

#### **Figure 21.**

*LHON: right optic disc seems to be elevated with peripapillary telangiectatic vessels. About the left optic disc, it has mild temporal pallor.*

#### **Figure 22.**

*OCT of LHON: mild peripapillary sectoral RNFL edema in both eyes with a decrease in temporal sector of peripapillary RNFL thickness in the left eye.*

#### **Figure 23.**

*OCTA of LHON: A, B, C, acute phase of the disease. Optic disc is hyperemic with peripapillary telangiectatic vessels. C, E, F, three months after the onset of the signs, significant capillary dropouts in the temporal side (papillo-macular bundle) and disc cupping are visible.*
