The Mysterious Case of the Elusive 5 Diopters of K
The Patient was 80 years old and the father of a prominent doctor in town. He had traveled from the Phillipines to have cataract surgery performed in his right eye by my doctor. Pt Complained of gradual decrease in overall VA OD > OS x 3 yrs. ROS, PFSH were noncontributory and he had no history of ocular surgery. WRx was -2.00 sph OD with VA 20/100 and -1.50 sph OS with VA 20/50. Uncorrected VA was not measured.
The Refraction His BCVA (MRx) was 20/80 OD with -2.50 +0.75 x 180 and 20/30 OS with -2.00 +0.50 x 180 OS. Pupils, VF to C, Motility were all unremarkable.There were no auto-refractor findings as we did not have an AR in our office then and old records were not available due to him being from overseas.
Exam revealed dense NS and dense cortical opacities OD > OS with healthy maculas and ONs although the view of the macula was difficult OD.
Impression & Plan: Medically ready cataracts OD > OS. After informed consent was obtained, Cataract Extraction with a standard IOL OD was scheduled with a target refraction OD of plano. The patient was counseled that he would likely need only reading glasses OD after cataract surgery.
Pre-op Measurements: I was tasked to perform this patient's pre-op IOL measurements and calcs. This patient was one of my favorites not just because he was always smiling and friendly, but also because he was known for his cool ties. He always came into the office in a suit and tie and it was great fun seeing what funny or cool tie he would wear. This day he was wearing a 'Flintstones' tie. Time to do the scan! Yabba Dabba Do!
Manual Keratometry K's showed OD were 42.00/47.00 @ 90 and OS were 41.87/47.00 @ 90. I was surprised by this as he was not wearing nor was he refracted to anything close to 5 D of cyl at 90!
This Calls for Some Sleuthing I decided to perform streak retinoscopy to rule out uncorrected refractive error. It was important to document more data to prove or disprove that this cyl was real. It was important to perform the retinscopy prior to the AScan so the cornea is not altered.
If this patient needed 5 D of cyl but wasn't wearing it, the tech who did his refraction may have missed it as it is sometimes difficult to find in a standard refraction. Many times patients with large uncorrected refractive errors can't lead the tech subjectively to their true correction there because their VA is so blurry. If his VA could be corrected with the cylinder enough to satisfy his patient's visual demands, then cataract surgery was not warranted now.
Retinoscopy findings were close to the MRx: - 2.75 + 0.50 x 180 OD and -2.00 + 0.50 x 180 OS. Hmmmm... there was only one explanation.
The AScan was performed and showed an average AXL OU.
Time to Talk with the Surgeon I presented this chart to the surgeon. I told her I suspected he had lenticular AND corneal astigmatism oriented at opposite axes and the lenticular astigmatism essentially cancelled out the corneal astigmatism. This explains why his retinoscopy findings and subjective refraction were nearly spherical but the keratometer revealed otherwise. She called the patient to come into the office for a talk.
The Surgeon Counsels the Patient The surgeon explained to the patient that our measurements showed he had significant astigmatism and would have it also after the cataract was removed. She explained why. He said was not aware that he ever had astigmatism. The surgeon explained she would perform an additional procedure during the cataract surgery to minimize the amount of residual corneal astigmatism he would have but likely she could not eliminate it and he WOULD need glasses for distance AND near post operatively. This discussion was documented in the patient's record and his target Rx OD remained at plano, with a note that he was told he would require spectacle correction for distance and near.
The surgeon proceeded as planned without complications. The surgeon performed Limbal Relaxing Incisions which decreased his post operative residual corneal astigmatism to 2 D. The patient was fit with Bifocals postoperatively and was pleased with his visual outcome (after he become accustomed to wearing 2 D of cyl!). A month later he had cataract surgery OS with a similar outcome. The patient flew home to the Philippines pleased; however, we sure did miss seeing him after he left.
Lesson Learned This case demonstrates why ophthalmic medical personnel must have a thorough knowledge of anatomy, physiology, refractive errors and instrumentation and be able to put 2 and 2 together. If this patient had not received appropriate testing and counseling, he may have been disappointed and surprised to learn he had a significant postoperative refractive error. He also may have been displeased that he had to become accustomed to astigmatic correction. Additionally, if the retinoscopy was not performed prior to the AScan there may have been a question as to whether cataract surgery was medically necessary.
As you work up your patient ask yourself "Does this make sense?" Using all of your collective knowledge helps you know if things are adding up. If they don't, do additional investigations to determine why. Happy Sleuthing!