Tonometry Lecture Notes PDF

Attendance code QZ-QO-FH Attendance code: Lecture 5: Tonometry Ellie Livings OPT505  Attendance code: Intended Learning Outcomes Understand the term ’intraocular pressure’ Be aware of the factors that affect intraocular pressure (IOP)...

Attendance code QZ-QO-FH Attendance code: Lecture 5: Tonometry Ellie Livings OPT505  Attendance code: Intended Learning Outcomes Understand the term ’intraocular pressure’ Be aware of the factors that affect intraocular pressure (IOP) Understand the importance of measuring IOPs Begin to understand how to measure IOP Understand different tonometry techniques Pros and cons of contact and non- contact tonometry How and when to refer  Attendance code: Main relevant GOC core competencies O3.1 Undertakes safe and appropriate ocular examinations using appropriate techniques and procedures to inform clinical decision-making within individual scope of practice. O3.4 Analyses visual function from a range of diagnostic sources and uses data to devise a clinical management plan for a patient in areas that include the following: Ocular and systemic disease 03.5b (iv) Accurately identifies patients’ conditions and their potential need for medical referral in a timely way, including when urgent or emergency attention is required.  Attendance code QZ-QO-FH Tonometry= measuring the IOP An eye is a fluid filled sphere. -2 main chambers: anterior (aqueous) and posterior (vitreous) -The aqueous fluid is generated and drained in a continuous process. -The rates of aqueous generation and drainage gives rise to the intra-ocular pressure (IOP) IOP should ideally remain within a safe limit: not too high or low -If it gets too high, it squashes the structures inside the eye -If it gets too low, they are not supported  Attendance code QZ-QO-FH Aqueous Circulation Produced: Non-pigmented ciliary epithelial cells of the pars plicata 2ndry exit: 10- Circulates into 30% via the anterior uveoscleral chamber via outflow pupil pathway 1ry exit:70- 90% via trabecular meshwork and canal of Schlemm  Attendance code QZ-QO-FH Anterior Chamber Angle Fu, Huazhu & Xu, Yanwu & Lin, Stephen & Wong, Damon & Baskaran, Mani & Mahesh, Meenakshi & Aung, Tin & Liu, Jiang. (2019). Angle-Closure Detection in Anterior Segment OCT based on Multi-Level Deep Network. IEEE Transactions on Cybernetics. PP. 10.1109/TCYB.2019.2897162.  Attendance code QZ-QO-FH Anterior Chamber Angle ”…majority of the narrow angle patients were of low risk and it is probable that these patients would not require a PI without any other evidence. Common practice however is to offer all of these patients a peripheral iridotomy. ” Jain N, Zia R. The prevalence and break down of narrow anterior chamber angle pathology presenting to a general ophthalmology clinic. Medicine (Baltimore). 2021 Jun 18;100(24):e26195. doi: 10.1097/MD.0000000000026195. PMID: 34128851; PMCID: PMC8213274.  Attendance code QZ-QO-FH Gonioscopy https://www.touchophthalmology.com/glaucoma/journal- articles/gonioscopy-a-primer/ https://www.yoptoms.com/Blog/10498873  Attendance code QZ-QO-FH Dilation, ACA and the IOP If we are going to dilate a patient, we must: 1) Check IOPs 2) Check anterior chamber angle (AC) (Van Herricks technique) 3) Check allergies/contraindications 4) Driving status Record: 1) Drop info, time and date 2) Advice given 3) Give px CoO information sheet on drops used 4) Post-dilation IOP* https://www.college-optometrists.org/patient-resources  Attendance code QZ-QO-FH Caution: When not to Dilate? Weigh pros/cons, what is in the px’s best interest? -cases of known drug allergy -pregnancy 1st trimester (v small risk) punctal occlusion -Iris-fixed IOL -Following pupil signs with head trauma -Occludable narrow angles -Px taking miotics for glaucoma (rare now) -lens subluxation -suspected penetrating ocular injury Work within scope of practice, call hospital for advice if unsure  Attendance code QZ-QO-FH When do we measure IOP? People aged 40 (35) or over Family history of glaucoma (direct family member) Suspicious discs/ asymmetric discs Prior to dilation Assist with detection of some ocular diseases Narrow anterior chamber angles Patients with painful, red eye (if possible-which technique?)  Attendance code QZ-QO-FH What is a normal IOP? Normal range between 8 and 21mmHg BUT… Significant fluctuations in IOP, even in healthy eyes A large overlap between normal & glaucomatous IOP damage threshold varies (OHT & NTG) Lower IOP can be normal, Higher IOP can be normal for the px We can use knowledge of average IOP, known variations and guidelines from the NHS to help us determine whether IOPs are normal or abnormal  Attendance code QZ-QO-FH Ideal IOP 3 D) is to align the red mark of the prism with the axis of the minus cylinder. European Glaucoma Society Terminology and Guidelines for Glaucoma, 4th Edition - Part 1 Supported by the EGS Foundation British Journal of Ophthalmology 2017;101:1-72.  Attendance code QZ-QO-FH Troubleshooting If mires unequal in size: If mires are too thin: Move probe to largest Add more fluorescein If mires too thick: Remove probe, blot with tissue and try again If mires aren’t centred: Move probe towards bulk of image  Attendance code QZ-QO-FH Perkins Contact Tonometry Same principle as GAT Own light source and viewing system Coiled spring and counterbalanced mounting, so can be used on patient sitting or lying down Patient set up the same as for GAT  Attendance code QZ-QO-FH Perkins Advantages Disadvantages Directly comparable to Goldmann Corneal anaesthesia required Some question over whether NICE will accept readings Requires skilled operator Portable Magnification and lighting not as good so can be more difficult to see inner mires accurately Can be used with patient sitting or supine Less stable than GAT - difficult to gain steady view of mires - greater risk of corneal staining Easier to manipulate eyelids Problems with scarred corneas and nystagmus Accurate Subjective endpoint Low cost  Attendance code QZ-QO-FH Perkins set up 1. Clean down equipment 2. Insert probe into holder, ensuring bi-prism is horizontal 3. Switch on Perkins 4. Set dial to approx. 16mmHg  Attendance code QZ-QO-FH Perkins procedure 1. Headpiece rested on patient’s forehead and locked so it doesn’t move 2. Look through the observation piece as you move towards eye 3. Make contact with the cornea 4. The force is then adjusted until the applanated area has a diameter of 3.06mm 5. The prisms in the probe shift the upper half of the field of view to the left and the lower half to the right 6. The centre of the two halves are separated by a distance of exactly 3.06mm 7. When the applanated diameter is exactly 3.06mm the inner edges of the semi- circles will be in contact  Attendance code QZ-QO-FH Calibration Regular calibration needed in order to maintain accuracy: Monthly calibration check needed – Adjust readings to compensate for small errors – Return for service if 2.5mmHg or more error 40-50% of tonometers are incorrectly calibrated at any given time – This could be because 85% of people do not check The procedures for calibrating Goldmann and Perkins tonometers are in your Clinic Book and in the following videos – Make sure that you know how to do it – Ask in the practicals if you need clarification  Attendance code QZ-QO-FH When IOP is a problem (high /low) Intraocular inflammation (Uveitis) Choroidal detachment Glaucoma Fluid leakage Retinal detachment  Attendance code QZ-QO-FH IOP and glaucoma The higher the IOP, the higher the risk of Glaucoma IOPs over 30mmHg are dangerous CRVO & acute ONH damage Main form of glaucoma = primary open angle glaucoma (POAG) “Optic nerve damage, visual field loss and an IOP of 24 mmHg or over” But… Normal Tension Glaucoma (NTG) (approx. 33%) have IOP