Lasers in Diabetic Retinopathy

Dr Debdulal Chakraborty

Consultant

Vitreoretina service

Sri Sankaradeva Nethralaya

Guwahati

E mail devdc@rediffmail.com

Tel no 0361 2228921

Fax no 0361 2228878

 

n      Diabetic retinopathy is one of the leading causes of acquired blindness under the age of 65 yrs.

n      A large percentage of this blindness can be prevented with proper examination and Rx by ophthalmologists

Vision threatening complications of diabetic retinopathy include macular edema, haemorrhage, retinal detachment, and neovascular glaucoma

Prevalence of diabetic retinopathy

n      18% of patients with DM for 5 years

n      98% of patients with DM for 15 years

Unfortunately, patients who are not properly referred for evaluation and management or those who, for any reason, fail to get proper care from an ophthalmologist, are at the greatest risk of vision loss.

 

n      German ophthalmologist Gerd Meyer-Schwickerath first used photocoagulation for the eye.

n      He experimented with natural sunlight and a heliostat and then a carbon arc lamp before the xenon photocoagulator was developed

n      This light source would later be replaced by the first ophthalmic lasers

n      Thus far photocoagulation has remained the only established non-invasive mode of Rx for DME & PDR that has not reached a stage warranting surgery.

 

n      LASER is an acronym for Light Amplication for Stimulated Emission of Radiation

n      Laser light is Monochromatic & Coherent

n      Therefore it can be pointed at one spot on the retina very accurately.

 

 

Argon green (514 nm) or double freq NdYAG (532 nm) are the preferred laser wavelengths for treatment of diabetic retinopathy.

 

Treatment goals in PDR

Decrease complications of diabetic retinopathy such as rubeosis, vitreous hemorrhage, tractional and combined retinal detachment

 

Treatment goals in CSME

Resolution of retinal thickening & in some cases absorption of hard exudates.

 

Indications of laser

n      Focal / grid laser indicated in CSME

 

n      Panretinal laser Indicated in PDR with high risk characteristics

NVD to ⅓ disc area

NVD associated with Pre ret / vit haem

NVE disc area with Pre ret / vit haem Rubeosis iris

 

 

Laser settings in PRP

n      Wavelength

Argon green, Double freq NdYAG, Dye yellow, red or diode laser

n      Duration - 0.1 0.5 sec

n      Spot size 300- 500

n      Intensity -

moderately intense burn

n      No of burns / day - 900

 

Laser settings in Focal/ Grid

n      Wavelength

Argon green, Double freq NdYAG,

dye yellow, red or diode laser

n      Duration - 0.1 sec

n      Retinal spot size -50-200

n      Intensity light retinal burn

n      No of spots variable

 

Panretinal photocoagulation

n      Anterior edge should extend beyond the equator

n      Posterior edge includes an area 500 nasal to optic disc margin and 3000 temporal above & below foveal center.

n      Laser may extend within vascular arcades for retinal NV within 3000 from centre

n      When the compliance for follow-up is doubtful, laser may be performed in eyes with PDR without HRC.

n      Photocoagulation of CSME (if coexistent) is done 4 weeks prior to PRP or along with first session of PRP since scatter photocoagulation may worsen macular edema.

Various Lenses are used for laser such as mainster standard, high magnification etc

 

Post-laser follow-up

n      There are no post op physical restrictions

 

n      The first routine follow-up visit is scheduled for 4-6 wks following completion of PRP

 

n      Individual variation in examination may be warranted

Causes for Additional laser are-

n      Multifactorial

n      Individualised

n      Enlarging NV

n      Increasing activity of NV

n      freq / extent of vit haem

Additional laser may be done anterior to, posterior to or in between previous laser

Treatment at any given sitting of more than 1000 burns is not recommended due to higher risk for the iatrogenic development of CME, choroidal effusion, exudative retinal detachment, and angle closure.

Patients are told that there would be mild discomfort following the treatment session and also instructed to return immediately if severe pain occurs.

 

Mechanism of action of laser

  1. Conversion of hypoxic to anoxic retina reducing stimulus for neovascularization,
  2. Decreased oxygen requirement of inner retina,
  3. Improved oxygen transport through RPE,
  4. Liberation of vaso-inhibitive factors,
  5. Induction of posterior vitreous detachment.

 

Side effects of photocoagulation

n      Inadvertent foveal burn

n      Secondary choroidal neovascularization

n      Exacerbation of edema

n      Delayed dark adaptation

n      Mild restriction of peripheral visual fields.

n      Secondary RD due to "heavy treatment"

n      Vitreous hemorrhage from NV during laser

 

Before starting laser,

n      One should try to make it a point to start the laser sessions once the blood sugar and lipid levels are well controlled.

n      The laser efficacy increases manifold in a systemically stable patient.

Long term metabolic control results in decreased incidence & progression of DR

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