Clinical examples of correct orientation of a toric intraocular lens in patients with postkeratotomic corneal ectasia

BACKGROUND: Surgical treatment of cataract in patients with postkeratotomic corneal ectasia has various features. First, difficulties arise when calculating the optical strength of an intraocular lens and its cylindrical component and determining the location of the main axes of astigmatism for toric intraocular lens implantation. Additionally, not all modern keratotopography installations are able to accurately determine the refractive power of the cornea in such patients owing to pronounced irregular astigmatism and a large difference in keratometric parameters in the main meridians.

CLINICAL CASES DESCRIPTION: Two clinical cases of surgical treatment of cataract in combination with postkeratotomic keratectasia are presented. Patients underwent a standard preoperative ophthalmological examination. TMS-4 Tomey keratotopograph was used to accurately determine the refractive power of the cornea. The optical power of toric intraocular lens were calculated using the Holladay 2 formula with amendments for radial keratotomy and the Johnson & Johnson VISIC online calculator. SN6AT9 intraocular lens (Alcon) and a Tecnis ZCT800 toric intraocular lens (Johnson & Johnson) were implanted in patients. The orientation of the position of the cylinder axis of toric intraocular lens was performed perpendicular to the most flattened meridian, corresponding to the position of the keratectasia zone, determined by the most expanded keratotomy scar. Before surgery, the best corrected visual acuity of patient M was OD=0.2, OS=0.4 and that of patient K was OD=0.4, OS=0.2. After surgery, the best corrected visual acuity of patient M was OD=0.8, OS=0.8 and that of patient K was OD=0.8, OS=0.7.

CONCLUSION: This study aimed to familiarize practicing ophthalmologists, clinical residents, and postgraduates with a possible treatment option for cataracts by phacoemulsification with implantation of a toric intraocular lens in patients with postkeratotomic keratectasia. The resulting high visual acuity and subjective satisfaction of patients indicate the accuracy of chosen treatment tactics. A reliable visual guide for choosing the cylinder axis is the meridian of the greatest degree of keratectasia (cornea flattening), which is determined by the maximally expanded keratotomy scar position. The intraocular lens cylinder axis is oriented perpendicular to the keratectasia meridian. Ultrasound phacoemulsification of cataract with implantation of a toric intraocular lens is an effective method for correcting induced ametropia after radial keratotomy against the background of postkeratotomy keratectasia with high astigmatism.