חַשְׁכַת מִן רוּגְזִי עַיְינַי אִתְבְּלִיאַת בְּכָל מְעִיקָי.
1. has grown dim | עשׁשׁ – The word appears only twice more in Tanakh (in Tehillim 31:10-11), and from context appears to mean "to dim", "waste way" or "decay". See Rashi that the verb might relate to the noun עששית (lantern) in Mishnaic Hebrew, whose glass causes the candle inside to appear dimmer. Cf. Ibn Ezra that it relates to the word "עָשׁ", a moth, referring to the decay it causes as it eats clothing and the like.
2. from grief | מִכַּעַס – Though in modern Hebrew, "כַּעַס" means anger, in Biblical Hebrew it might also refer to sorrow or worry and vexation, as per its usage in Shemuel I 1:6,15 and Kohelet 1:18.
3. has aged | עָתְקָה – See Rashi and Metzudat Zion. The root "עתק" means "to move from one place to another" or "to advance", and hence can also take the connotation of advancing in years or growing old. Cf. Malbim who suggests that the psalmist is speaking of a literal removing of the eyes, or R"Y Kara that it refers to "removing [light] from the eyes".
4. my adversaries | צוֹרְרָי – The mention of enemies appears unconnected to the previous focus on sickness. See Ibn Ezra that the psalmist might refer to those foes who rejoiced at his misery, or Malbim that the palmist was afflicted by both disease and an attack by enemies.