CORNEAL DIAMETER-HVID

OPTOM FASLU MUHAMMED

Technique 1:  Corneal Topographer :use the biometric ruler

within the corneal topography software program to measure your patient’s horizontal visible iris diameter (HVID).

  It may be necessary to measure at a 45 degree oblique angle as the topographer may cut off part of the cornea in the horizontal plane. 

For accuracy and consistency, always measure from the white part of one side of the eye directly across to the white part of the other side of the eye. 

Reference the example image below; the corneal diameter or visible iris diameter measures 12.01mm.

Technique 2:  :  Slit Lamp & Reticle – remove an eye piece from the slit lamp and insert the reticle. 

Use the slit lamp and integrated reticle to obtain a direct horizontal measurement of the patient’s visible iris diameter. 

Reference the example image below; the corneal diameter or horizontal visible iris diameter measures 11.8mm

Technique 3:  Loupe, 7X, Peak Scope – this device is commonly used for measuring the diameter of a GP contact lens, but can be an easy and efficient method to measure the horizontal visible iris diameter (HVID).  Looking through the loop get close to the patient’s cornea; almost uncomfortably close similar to direct ophthalmoscopy. 

Use the measurement ruler built within the loop to measure the patient’s HVID as accurately as possible.  Reference the example images below.

HVID- ( SIMPLE MILLIMETER SCALE)

Cornea is a curved surface so an easy way to measure its diameter is by measuring the HVID-horizontal visible iris diameter.

This measurement is taken by a simple millimeter scale, measuring the limbus to limbus size both across the horizontal length.

The corneal diameter aids in determination of the Total diameter of the contact lens.

CORNEAL DIAMETER

HVID=10 to 14mm(average:11.6 to 12.0mm)

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