Сборник полезных фактов по поведению цилиндров при разных патологиях:
1) Limbal dermoid - flattest meridisn of cornea is adjacent to it
2) pterygium - flattens the onvolved meridian, changes central ast.
3) Terrien's corneal degeneration - ATR Ast. (if starts superiorly)
4) pellucid M.D. - irregular high Ast.
5) Astigmatic keratotomy: incision to be put perpendicular to the steepest meridian (6-7 mm away from center, arcuate or transverse; the closer - the bigger effect)
6) tight radial suture in the cornea - adjacent cornea is flattened, curvature along that meridian is increasing, perpendicular meridian's curvature is decreasing; the deeper suture the more effect on curvature; the closer to the center the more effect on curvature)
7) RK flattens both ant. and post. corneal surfaces in small central optical zone (persists for several months; hyperopic sgift - for years)
8) Cataract surgery - corneal edema flattens the cornea centrally
9) Excimer laser flattens anterior surface, but not posterior (normal ant/post corneal curvature ratio altered!)
10) Pterygium: every 1,1 mm of cornea involvement gives ~ 1D of WTR irregular corneal astigmatism - flattening)
11) RLI - at the steepest meridian; for ATR Ast - at 9 or 3 o'clock, WTR - 12 or 6 o'clock
12) Toric IOL rotated 90 degree away from needed axis - residual Ast will increase.
13) Superior sclerocorneal tunnel incision -> will drift Ast towards ATR (and decrease WTR): cyl -2,0/180 (K1 40, K2 42) -> will be eliminated with 6mm tunnel (1,5 +/- 0,5D elimination).
3,5 mm scleral incision will eliminate 0,5 +/- 0,3 cyl
14) Goldmann Tonometry: WTR Ast >3D -> underestimation
ATR >3D -> overestimation
15) Phaco/SICS incisions: 1D flattening at incision meridian will correspond with equivalent steepening (1D) at orthogonal meridian (almost 1:1). ~2,8 mm = flattening by 0,5D.
16) Congenital ptosis -> 90% WTR Ast, 6,7% -> ATR, 3,3% - oblique. 25,3% - high Ast; 27,5% - reduction of Ast postoperatively
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