India is the country with the second-largest number of people with Diabetes worldwide affecting about 72 million people, with 8.8% prevalence in adults according to the International Diabetes Federation. Diabetes causes an array of long-term systemic complications, which have a considerable impact on both the patient and the society because it typically affects individuals in their most productive years.
Diabetic Retinopathy
Diabetic retinopathy is defined as progressive dysfunction of the retinal vasculature caused by chronic hyperglycemia resulting in structural damage to the neural retina. Diabetic retinopathy is a leading cause of blindness and visual disability in diabetic patients. Risk factors of diabetic retinopathy are prolonged duration of diabetes, poor control of diabetes, hypertension (high blood pressure), diabetic nephropathy, hyperlipidemia, pregnancy, smoking, obesity and anemia.
The severity of DR can range from very mild, i.e., Non-proliferative type to very severe Proliferative type. NPDR, i.e. Non-Proliferative Diabetic Retinopathy is the early stage where the small blood vessels in retina leak, making the retina swell. PDR, i.e., Proliferative Diabetic Retinopathy is the severe form of diabetic eye disease in which there is growth of abnormal new blood vessels in the retina. It happens when abnormal new blood vessels start growing in the retina. This is called Neovascularization. The growth of new vessels can lead to a host of subsequent problems, including vitreous hemorrhage, tractional retinal detachment, and neovascular glaucoma.
Center of the retina i.e., “Macula”, the center of which is called “Fovea” is responsible for a sharp vision in human eye. Diabetic macular edema (DME) is the most common cause of vision loss among diabetic patients. DME is manifested as retinal thickening caused by the accumulation of intraretinal fluid. In macular ischemia, blood cannot reach the macula, thus affecting the vision permanently.
Diabetic Cataract
Cataract is an opacification of the lens of the eye which leads to a decrease in vision. Cataract is one of the major causes of visual impairment in diabetic patients. Patients with DM are reported to be up to five times more likely to develop a cataract, in particular at an early age. Due to increasing numbers of type 1 and type 2 diabetics worldwide, the incidence of diabetic cataracts steadily rises. Cataract surgery is the most common surgical ophthalmic procedure performed worldwide.
Cataract and Diabetic Retinopathy
Cataract surgery in diabetic patients may become necessary, not only to improve vision but also to allow assessment and treatment of diabetic retinopathy. Compared to non-diabetic patients, visual outcome after cataract surgery was reported to be worse in diabetic patients, especially in those with diabetic retinopathy.
Preoperatively in diabetics, it is recognized that there is a higher incidence of pigment dispersion and fibrinous reaction in the anterior chamber, together with the development of posterior synechiae, as well as increased risk of capsule rupture and vitreous loss. Cataract surgery in diabetic retinopathy is associated with a higher incidence of postoperative complications, including corneal decompensation, fibrinous uveitis, neovascularization of anterior segment, accelerated progression of diabetic retinopathy and macular edema.
Patients with pre-existing proliferative diabetic retinopathy are more likely to progress rapidly after cataract surgery, therefore panretinal photocoagulation (PRP) is recommended preoperatively. When lens opacity precludes PRP, it can be performed after surgery or the surgeon may consider preoperative panretinal cryopexy or combined cataract surgery with vitrectomy and endolaser photocoagulation, especially for cases with posterior pole tractional retinal detachment (TRD). Treatment of neovascular glaucoma must take priority over cataract treatment because prolonged increase in intraocular pressure can cause permanent damage to the optic nerve and severe visual loss. Macular edema should be adequately treated prior to surgery because pre-existing maculopathy may aggravate postoperatively and is strongly associated with a poor visual outcome. Treatment of the maculopathy maybe with laser photocoagulation or pharmacotherapy with intravitreal injections of anti-VEGF agents or steroids
Prior to surgery, patients should have good glycemic control and no evidence of ocular or periocular infection. Thorough and comprehensive ophthalmologic examination including assessment of visual acuity (VA), best-corrected visual acuity (BCVA), relative afferent pupillary defect (RAPD), slit-lamp biomicroscopy, gonioscopy (with particular attention to new vessels), tonometry and dilated fundoscopy is mandatory. Ancillary diagnostic evaluations such as fluorescein angiography, optical coherence tomography (OCT) and B-scan ultrasonography may be helpful in the selected case.
Surgical outcome in patients without diabetic retinopathy is comparable to non-diabetic patients, and the outcome of patients with retinopathy appears to depend on the degree of retinopathy at the time of surgery. In general, patients with mild non-proliferative retinopathy without laser indication have been proposed to have a good prognosis. Diabetic patients with severe non-proliferative diabetic retinopathy and proliferative diabetic retinopathy have a high risk of progression of diabetic retinopathy following cataract surgery.
Therefore, performing cataract surgery at an earlier stage is often beneficial for diabetic patients because it is associated with fewer complications and better postoperative recovery of sharp vision.
Cystoid macular edema is about 14 times more common in diabetics than in nondiabetics. Macular edema is the most frequent cause of poor visual acuity after cataract surgery in patients with diabetes mellitus. Clinically significant macular edema (CSME) present at the time of surgery is likely to progress and eyes with previously treated CSME are at increased risk of recurrence. The risk of progression is increased if the operation is complicated by excessive manipulation, vitreous loss, or severe post-operative inflammation. Risk factors associated with worsening retinopathy after cataract surgery include pre-existing severe retinopathy, poor glycemic control, increasing age and posterior capsular disruption.
The progression of diabetic retinopathy may be caused by breakdown of the blood ocular barrier or enhanced inflammation in diabetic patients after cataract extraction. The smaller incision size and shorter surgical time in phacoemulsification decrease inflammation and may induce less breakdown of the blood ocular barrier.
Postoperatively topical non-steroidal anti-inflammatory drugs in addition to routine topical steroid preparations, are prescribed because they control inflammation and may play a role in the prevention and treatment of macular edema. Macular thickness can be evaluated at serial postop visits via OCT before the topical medications are stopped. Patients should aim to keep their systemic blood glucose levels controlled during the postoperative period to aid with healing.
