What is the role of cryotherapy in treating absolute glaucoma?

Cryotherapy for Absolute Glaucoma

Cryotherapy is now rarely used for absolute glaucoma as laser cyclophotocoagulation causes less postoperative pain and inflammation while achieving similar intraocular pressure reduction. 1

Understanding Absolute Glaucoma and Cyclodestructive Procedures

Absolute glaucoma refers to an end-stage, painful, blind eye with elevated intraocular pressure (IOP). Management focuses on pain control and IOP reduction through cyclodestructive procedures, which reduce aqueous humor production by targeting the ciliary body.

Types of Cyclodestructive Procedures:

• Cyclocryotherapy (using freezing temperatures) 1
• Transscleral and noncontact Nd:YAG laser cyclophotocoagulation 1
• Transscleral and noncontact endodiode laser cyclophotocoagulation 1

Current Role of Cryotherapy in Absolute Glaucoma

Limited Current Use:

• Cyclocryotherapy has been largely replaced by laser-based cyclodestructive procedures due to their superior side effect profile 1
• Success rates of cyclodestructive procedures generally range from 34% to 94% 1

Disadvantages of Cyclocryotherapy:

• More severe postoperative inflammation compared to laser procedures 1
• Greater postoperative pain than laser alternatives 1
• Risk of hypotony (abnormally low IOP) 1
• Potential for cystoid macular edema 1
• IOP spikes 1
• Frequent need for repeat treatments weeks or months later 1
• Potential for vision loss and rare cases of sympathetic ophthalmia 1

Preferred Modern Alternatives

Laser Cyclophotocoagulation:

• Now preferred over cyclocryotherapy 1
• Advantages over cyclocryotherapy include:
  • Less postoperative pain 1
  • Reduced inflammation 1
  • Technical ease 1
  • Reduced postoperative care 1
  • Avoidance of incisional surgery 1

Endoscopic Cyclophotocoagulation (ECP):

• Increasingly popular (65% of Medicare cyclophotocoagulation procedures by 2007) 1
• Uses 810-nm laser delivered through a fiberoptic cable 1
• Allows direct visualization and treatment of ciliary processes 1
• Enables better titration of laser treatment 1
• IOP reduction reported in the range of 34% to 57% 1
• Can be combined with cataract surgery when appropriate 1

Special Considerations for Neovascular Absolute Glaucoma

In cases of neovascular absolute glaucoma, some evidence suggests:

• Combined transscleral panretinal cryocoagulation with cyclocryocoagulation may be more effective than cyclocryocoagulation alone 2
• Anterior retinal cryoablation has shown promise as a preliminary procedure before filtering surgery or drainage implant surgery 3

Treatment Algorithm for Absolute Glaucoma

1. First-line approach: Transscleral cyclophotocoagulation or endoscopic cyclophotocoagulation 1
2. Consider cyclocryotherapy only when:
   • Laser equipment is unavailable 1
   • Patient has failed laser cyclodestructive procedures 1
   • Special circumstances like neovascular glaucoma where combined approaches might be beneficial 2, 3

Pitfalls and Caveats

• All cyclodestructive procedures carry risks of vision loss, hypotony, and phthisis bulbi (shrinkage of the eye) 1
• Cyclocryotherapy specifically has higher risks of severe inflammation and pain compared to laser alternatives 1
• Multiple treatments may be required regardless of the cyclodestructive method chosen 1
• Careful patient selection and informed consent regarding potential complications are essential 1