Glaucoma progression after cataract surgery
New baseline warranted postoperatively due to potential impact of cataract removal and IOL choice
Findings on glaucoma diagnostic tests can change after phacoemulsification cataract surgery, said Carroll A B Webers, MD, at the 2020 ESCRS Virtual meeting.
Therefore, it is very important to have a new baseline measurement after phacoemulsification and IOL implantation in a glaucoma patient, he advised.
Addressing the question, “Does an IOL choice impact my glaucoma diagnostics”, during a session on glaucoma pearls for the cataract surgeon, Dr Webers reviewed changes in standard white-on-white perimetry parameters measured with the Humphrey Field Analyzer and on OCT-measured peripapillary nerve fibre layer (PP NFL) thickness in glaucoma patients.
IMPACT ON VISUAL FIELD
His discussion of visual field changes focused on foveal sensitivity, mean deviation (MD) and the Visual Field Index (VFI).
Dr Webers said that the fovea threshold, which is the retinal sensitivity in the fovea, is generally increased (improved) after phacoemulsification. The MD, which is a weighted average of the values presented in the total deviation plot (ie, the mean depression of the patient’s overall visual field), is also improved after cataract surgery. Similarly, the VFI, which is an enhancement of the MD, also generally improves.
“However, the VFI is less affected by cataract and it is more sensitive to changes near the centre in order to better correlate with the ganglion cell loss,” said Dr Webers, Professor and Chair, Department of Ophthalmology, Maastricht University, Maastricht, The Netherlands.
He also noted that the impact of phacoemulsification on the visual field parameters will vary depending on the density and type of cataract and on the glaucoma stage, determined by the number of defects, the depth of the defects and their localisation. Dr Webers illustrated this point by discussing three case examples.
The first case involved a patient with a relatively dense cataract and mild glaucoma whose VF showed multiple changes, including improvements in foveal sensitivity, MD and VFI. He contrasted the visual field effects in that case with those of a case of a patient who had end-stage glaucoma. In this latter case, the visual field showed an increase in foveal sensitivity, but neither the MD nor VFI had changed.
“The MD and VFI values in this patient are mostly caused by the glaucoma and not affected so much by the cataract. The foveal sensitivity, however, increased since the cataract was removed,” Dr Webers explained.
The third example described a patient with moderate glaucoma in whom cataract density would be a more critical factor for predicting visual field changes. In such a case, any change can occur on the visual field, Dr Webers said.
“Normally the fovea sensitivity will stay the same or increase – it depends on how far the scotoma reaches. The MD change will depend on the intensity of the cataract, improving if there is a lot of cataract and staying the same if there is only little cataract,” he explained.
Discussing the impact of IOL choice on the VF parameters, Dr Webers noted there is little literature relating to this topic in normal eyes and even less pertaining to patients with glaucoma. Summarising the available information, he said that on average, a monofocal IOL will have minimal to no effect on the MD value while a multifocal IOL will be associated with a significant nonspecific reduction of up to -3dB.
“This loss does not improve with time or neuroadaptation. The reduction seems to be related to the multifocal design of the implant rather than to pseudophakia, and is a generic property for all diffractive IOL types,” he said.
Reports in the literature are relatively consistent in showing that PP NFL thickness in normal eyes increases following cataract extraction in the range of +4 to +19μm. Data on the change in patients with glaucoma are limited, but the available reports indicate that an increase in PP NFL thickness is also seen after cataract surgery in eyes with primary open angle glaucoma.
“I found a single study investigating patients with pseudoexfoliation glaucoma that found no change in PP NFL thickness, but it also found no change in normal control eyes,” Dr Webers said.
The postoperative increase in PP NFL thickness following phacoemulsification is seen regardless of the OCT machine used and is the result of an increase in signal strength following cataract removal, Dr Webers said.
“The cataract impedes signal transmission to and from the retina, and the delayed time-of-flight affects the delineation of the NFL, leading to a falsely low measurement,” he explained.
Information on potential differences relating to cataract type is variable.
“Some papers say the impact is greatest with nuclear cataracts, others say it is more with cortical cataracts, and even others say it is more with posterior subcapsular cataracts.”
Quotes cited from various papers addressing the impact of IOLs on OCT imaging show some lack of agreement. However, Dr Webers concluded that OCT image quality can be affected by multifocal IOLs.
Carroll A B Webers: firstname.lastname@example.org