Management of Astigmatism in MSICS

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Manual small incision cataract surgery(MSICS) offers advantages with wider applicability, lesser time consuming, a shorter learning curve, and a lower cost. Technological advances in ophthalmology has grown by leaps and bounds. An ophthalmologist’s duty is not only to improve the vision but also to refine it. The target nowadays is to achieve emmetropia even if it is MSICS. This article deals with the management of astigmatism in MSICS. 

What is Astigmatism? 
Variations in the curvature of refractive elements of the eye which prevent light rays from focusing to a single point of retina.  


Types of astigmatism 

  • With the rule- steeper at the 90-degree axis and is more common in younger patients
  • Against the rule- steeper at the 180-degree axis and is more common in older patients and the patients who we deal during cataract surgeries.
  • Oblique astigmatism

Measurement of Pre-existing Astigmatism can be done by 

  • Keratometry- in patients with poor fixation, corneal abnormalities, distorted mires, highly toric cornea or dry cornea.
  • Corneal Topography- is preferred
  • Factors Affecting Astigmatism in SICS1 
  • Incision Characteristics 
  • Size of the incision- Larger the incision greater the flattening and vice versa. 
    Distance of the incision from cornea- Farther the incision from cornea lesser the astigmatism and vice versa.
  • Site of incision- Superior Incision Easy to learn 
    Wound is protected with the eyelid 
    Less Foreign body sensation
  • Temporal Incision 
    Easier in deep sockets 
    Small eyes 
    Conjunctiva is spared for future trabeculectomy
  • Supero-temporal Incision 
    Free from effect of gravity 
    Eyelid pressure tends to induce less astigmatism
  • Configuration of the incision 
    Straight, smile, frown, chevron and Blumenthal incision. 
    Frown incision is the preferred one. 
    Chevron and Blumenthal incisions induce the least astigmatism. 
    The target is to hit the “Astigmatically neutral zone” 
    A concept given by Paul Koch in 1990. It is funnel shaped with base at the limbus and as it moves away it widens. The incision which is made within this funnel is astigmatically neutral.  
     
  • Surgically Induced Astigmatism(SIA) 
  • Use of Cautery 
    Excessive cautery increases the Surgically induced astigmatism due to scleral shrinkage or necrosis.
  • Use of Suture 
    If we have to apply a suture, then we have to be aware of the astigmatism caused by it.  
    Tight suture causes steepening of the cornea while loose suture flattens it.
  • Management of Pre-existing Astigmatism 
    We should be aware of the theory of corneal coupling action which states that “When we flatten one meridian of the cornea, we will steepen the other meridian (90° away)” 
     
  • Mild Astigmatism 
    Can be neutralised by changing the site of the incision or 
    Varying the construction of the incision. 
    Always operate on the steep axis.
  • Moderate to High Astigmatism 
  • Limbal Relaxing Incisions(LRI) 
    To manage high pre-existing astigmatism, we can give LRI. 
    The incision should be of 90% depth (around 600 micron), on the steeper meridian and just in front of the limbus. 
    It is imperative to check the calculations to prevent any mishap. 
    Nomograms of Miller, Gill and Nichamin are helpful. There are online calculators too http://www.lricalculator.com. 
    Usually, 1 clock hour (30 degree) of paired incisions is used to treat 1D of corneal astigmatism. 
    They are easier to perform than shorter and centrally placed corneal relaxing incisions. 
    Paired LRIs exhibit consistent 1:1 coupling ratio which gives regular corneal flattening and less chances of irregular astigmatism.

 

  • Opposite Clear Corneal Incisions(OCCI) 
    Technique involves creating two bi-planar 3.2mm incisions 180 degrees from each other. 
    They are placed 1.5-2 mm inside the edge of the limbal vessels along the steeper meridian of the cornea.  
    The mean astigmatism correction achieved with this technique is 2.06 D. 4
  • Newer Advances 
    SMART SICS which uses the concept of Coupling. 
    Neutralises the steepness in the upper half of the vertical meridian and maintains the steepness of inferior hemi-meridian to give good bifocality.

References 

  1. Singh K, Misbah A, Saluja P, Singh AK. Review of manual small-incision cataract surgery. Indian J Ophthalmol 2017;65:1281-8
  2. Gokhale NS, Sawhney S. Reduction in astigmatism in manual small incision cataract surgery through change of incision site. Indian J Ophthalmol 2005;53:201-3.
  3. Burgansky Z et al. Minimal astigmatism after sutureless planned extracapsular cataract extraction. J Cataract Refract Surg 2002;28:499-503.
  4. Khokhar S, Lohiya P, Murugiesan V, Panda A: Corneal astigmatism correction with opposite clear corneal incisions or single clear corneal incision: comparative analysis. Journal of cataract and refractive surgery 2006; 32:1432-7. 
     

By,

Dr. Pranav Saluja 
Regiional Institute of Ophthalmology 
Motlal Nehru Medical College 
Allahabad 
E-mail id : saluja.pranav@gmail.com