Outcomes of Subthreshold Laser Versus Intravitreal Injection of Ranibizumab in Diabetic Macular Edema

Diabetic macular edema (DME) causes significant visual loss in diabetic patients. About 20% and 40% of patients with Type 1 and Type 2 diabetes mellitus (DM), respectively, develop DME. One-third of diabetic patients who have had DM for more than twenty years will develop DME . Early impairment in the function of the middle and inner layers of the retina has been reported in diabetic patients before appearance of vascular complications . A good independent guide of macular function in patients with DME is multifocal electroretinogram (mfERG) readings from the macular area, which strongly associate with morphologic alterations in the macula. Some investigators suggested that temporal characteristic (implicit time) of mfERG waves are more important than amplitudes for evaluation of retinal function in diabetic patients. They concluded that patients with DM show temporal changes indicating delayed neural transmission due to local impairment of blood glucose metabolism. In contrast, others emphasize the importance of both parameters (implicit time and amplitude) in identifying retinal affection in DM.

Intravitreal (IV) injections of anti-vascular endothelial growth factor (VEGF) agents provided good visual outcomes in treatment of DME. However, IV anti-VEGF injections are expensive, need to be repeated many times and have the potential risk of causing endophthalmitis . Subthreshold micropulse laser (SML) treatment of DME has the same effect as conventional laser treatment, nonetheless, there is less damage to adjacent tissues of the burn area in the retinal pigment epithelium (RPE). SML allows laser emission to be divided into bursts of short cyclic pulses that remain for microseconds permitting substantial cooling amid these short pulses .

Inclusion criteria

• DME with BCVA<0.5 decimal Snellen acuity.
• Controlled blood glucose (HbA1c) <6.5%.

Exclusion criteria

• History of previous intraocular surgery,
• History of previous laser treatment,
• History of previous IV injection,
• Macular disease or ischemia,
• Proliferative diabetic retinopathy,
• Vitreoretinal traction,
• Interruption of external limiting membrane (ELM) or ellipsoid zone (EZ).
• Dense media opacity,
• Optic disc pathology
• History of strokes or ischaemic heart diseases.
• patients with (CST) > 400 µm on OCT .