Tích cực áp lực về phía trước áp lực tích cực về phía trước trên màng mống mắt ống kính thay đổi các lực lượng trên các viên trước và có thể gây ra mất kiểm soát của các rhexis rách ra vào zonules. Nếu có thể nguyên nhân của áp lực nên là 32 | CATARACT SURGERY Figure Capsulorhexis in a white cataract using trypan blue dye Vision Blue courtesy of Dorc edge is possible but requires considerable experience. It should be noted that the ideal capsulorhexis diameter should be larger than the small pupil in order to avoid synechiae between iris and rhexis margin. Positive forward pressure Positive forward pressure on the lens-iris diaphragm alters the forces on the anterior capsule and may cause loss of control of the rhexis with tearing out into the zonules. If possible the cause of the pressure should be identified. For example is the speculum pressing on the eye has a large volume of anaesthetic been used or has a suprachoroidal haemorrhage occurred If forward pressure cannot be relieved then the capsulorhexis should commence with an intentionally small diameter using pronounced centripetally directed traction on the flap with frequent small steps regrasping close to the tearing edge. Exerting counter pressure by pushing the lens back with a high viscosity viscoelastic is essential and additional viscoelastic should be injected if loss of control of the tear occurs. If the 32 CAPSULORHEXIS forward pressure is relieved the rhexis can then be increased in width. The intumescent white cataract The intumescent lens combines the difficulties of forward pressure with those of a lack of red reflex. Logically therefore all of the above mentioned advice should be observed. A forceps technique is preferable because the cortex is often liquefied and presents no resistance to a needle tip. The lens can be decompressed using a small puncture in the anterior lens vertex and some of the liquid content aspirated 13 but this carries a substantial risk of causing an uncontrolled capsule tear into the zonules. The fact that a wide variety of approaches are described to deal with the intumescent lens highlights the fact that there is no ideal method to tackle these technically difficult situations. Even the most experienced
