Roland Lee Changes in Intraocular Pressure and Anterior Chamber Spring 2010 Angle Following Cataract Surgery 1Comparison of Changes in Intraocular Pressure and Anterior Chamber Before and After Cataract Surgery Roland Lee ABSTRACT Cataract is the leading cause of blindness worldwide. Fortunately, cataract-induced blindness is reversible by cataract surgery. In addition to reclaiming lost vision, cataract surgery lowers intraocular pressure, but the reason for this remains unclear. Understanding the mechanism behind intraocular pressure reduction following cataract surgery has implication for treating glaucoma, which involves lowering intraocular pressure through glaucoma medications or surgeries. Adequate control of intraocular pressure through cataract surgery would render glaucoma treatment nonessential and could become an optimal solution for patients with co-existing cataract and glaucoma. To answer the research question of whether anterior chamber angle alteration induces intraocular pressure reduction, we compared changes in intraocular pressure and anterior angle before and after cataract surgery. Age, ethnicity, and gender are risk factors related to cataract development, but their effects on the degree of changes in intraocular pressure and anterior chamber angle following cataract surgery are unclear. The degree of change in intraocular pressure and anterior chamber angle following cataract surgery is evaluated in terms of these risk factors, to assess whether a relationship exist between them. Statistical analysis revealed a significant decrease in intraocular pressure and an increase in anterior chamber angle opening distance following cataract surgery. However, comparison of the degree of changes in intraocular pressure and angle opening distance in terms of age, ethnicity, and gender revealed insignificant difference within each group. In conclusion, we found that anterior chamber angle extension is a mechanism for intraocular pressure reduction following cataract surgery and this is consistent regardless of age, gender, and ethnicity. Repeated studies with this experimental design at other clinical sites are needed to substantiate the applicability of our findings to the general population. KEYWORDS Phacoemulsification, Glaucoma, Visual Acuity, Age, Ethnicity, GenderRoland Lee Changes in Intraocular Pressure and Anterior Chamber Spring 2010 Angle Following Cataract Surgery 2INTRODUCTION Cataract causes about 70% of blindness globally and is projected to account for vision impairment in more than 75 million people by 2020, but fortunately cataract-induced blindness is reversible by surgical intervention (Roodhooft 2002; Allen 2006). A cataract is any discoloration of the human lens that reduces its transparency and lowers light transmission through the eye (Bradford 1998). Left untreated, a cataract grows and progressively reduces vision until blindness occurs (Allen 2006). Surgery is needed to reclaim vision lost to cataract. In phacoemulsification, the most common surgical technique used in the developed world to address cataract, a surgeon makes a small incision through the cornea to expose the lens to a probe that emits ultrasound waves to break the lens into small pieces, which are suctioned out and replaced with an artificial lens (Bournias 2005). Cataract surgery has the beneficial side effect of intraocular pressure reduction, but the reason for this remains unclear (Issa et al. 2005). Noting a decrease in the outflow facility’s resistance to the aqueous humor flow after surgery, Meyer proposed that an improvement in the aqueous outflow facility of the eye leads to intraocular pressure reduction (Meyer et al. 1997). Resistance to the flow of aqueous humor elevates intraocular pressure in the eye (Bournias 2005). So a decrease in the outflow facility’s resistance should subsequently lead to lower intraocular pressure. Excluding Meyer’s work, no studies provide evidence for possible mechanisms behind reduction in intraocular pressure after cataract surgery. Identifying possible mechanisms for reduced intraocular pressure after cataract surgery has implications in the field of ophthalmology. Intraocular pressure is associated with glaucoma, the second leading cause of blindness in the world, which is projected to affect more than 60 million people by 2010 (Quigley and Broman 2006). Glaucoma treatment involves lowering intraocular pressure through medication or surgery (Bournias 2005). Better understanding of the mechanism behind intraocular pressure reduction after cataract surgeries may allow for adequate control of intraocular pressure through the phacoemulsification, which would render anti-glaucoma medications and surgeries nonessential to the treatment of glaucoma. This will eliminate the patient’s risk of side effects from anti-glaucoma medication or potential complications from glaucoma surgery. Furthermore, because some risk is associated with all surgical interventions, cataract surgery is currently only considered when the prospects for recovery of vision outweigh any possible surgical complications (Kim and Choi 2008). But if cataract surgery succeeds inRoland Lee Changes in Intraocular Pressure and Anterior Chamber Spring 2010 Angle Following Cataract Surgery 3adequately controlling intraocular pressure, this could lead to reformation of clinical guidelines, in which the prerequisites for cataract surgeries could be lowered for patients with co-existing cataract and glaucoma, as cataract surgery would be an optimal solution for such patients. Variationin the eye’s anterior chamber angle affects intraocular pressure (Bournias 2005). The anterior chamber houses the ciliary body, which produces aqueous humor, a watery fluid that circulates through the pupil, trabecular meshwork, Schlemm’s canal, and uveoscleral outflow facility. Resistance to the flow of aqueous humor anywhere along this pathway causes a rise in intraocular pressure. If the anterior chamber has a wide outflow angle, the aqueous humor is stored in a voluminous compartment with a spacious outlet, allowing for great ease of flow. But if the anterior chamber has a narrow outflow angle, the aqueous humor is confined in a small space with a tiny exit channel, resulting in more constricted flow (Bradford 1998). Intrinsic factors, including age, ethnicity, and
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