OPT505 Lecture 9: Accommodation & Eye Examination PDF

OPT505 Lecture 9: Accommodation & Eye Examination Ellie Livings Intended Learning Outcomes Understand the role, purpose and mechanism of accommodation Understand how accommodation is relevant in ametropia and its correction Know how to measure AoA Understand far point, range of accommod...

OPT505 Lecture 9: Accommodation & Eye Examination Ellie Livings Intended Learning Outcomes Understand the role, purpose and mechanism of accommodation Understand how accommodation is relevant in ametropia and its correction Know how to measure AoA Understand far point, range of accommodation, accommodative demand Know how to calculate accommodation required and range of accommodation Relevant GOC LO O2 Communication, O3 Clinical practice Undertakes safe and appropriate ocular examinations using appropriate techniques and procedures to inform clinical decision-making within individual scope of practice. -Refractive management -Paediatrics -Patients with learning disabilities & complex needs -Occupational optometry Interprets the results of history-taking and the examination of the refractive and ocular motor status Manages and dispenses appropriate spectacles for paediatric patients and for patients with complex or additional needs, including by adapting the practice environment and practice activity in line with individuals’ needs health of individual patients to inform clinical decision-making and care management plans.  Recap optics: Simple Myopia ∞ Dioptric power of eye too strong Axial length too long Point focus in front of retina Blur circle Too weak 0 Too strong Simple Hypermetropia Dioptric power of eye too weak ∞ Axial length too short Point focus (theoretically) behind eye Blur circle Dioptric power of eye and correcting lenses 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 correcting lenses 55 56 57 58 64 65 66 67 68 69 Dioptric power of eye Too weak= plus lens Too strong=minus lens Far point Near point Focus is at nea Far point Near point Focus is at nea  Near point Far point Focus is at nea Increase in effective ‘plus’ power of eye to see objects closer than Correct if emmetropic & infinity in emmetropic eye non-accommodated Slido Poll:  Simple Myopia: effect of accommodation ∞ Non-accommodated: Already near focused as myopic far point Minus correcting 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 lenses 0 Accommodated: even more near focussed (near point closer to px) ∞ Near point  Simple Hyperopia ∞ Non accommodated: blur circle beyond retina, DV is blurred 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 Plus Minus correcting correcting lenses lenses Accommodated for D: More plus power to eye, blur circle on retina, DV is clear. Requires effort. ∞ Accommodated for N: More plus power to eye, blur circle on retina, DV is Near point blurred, near vision is. Requires effort++.  ∞ 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 56 57 58 59 60 61 62 63 64 65 Too weak ∞ OR a plus lens Simple hyperopia corrected for D with plus lens=no effort @ D Still needs to accommodate to see at near. End goal of refraction: =point focus on or just behind retina 9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9  Accommodation: Range In an emmetropic (or distance- corrected px), the accommodation stimulus when looking at a near object is the reciprocal of the target distance (m) The distance between the far point of the eye and the near point of accommodation is called the range of accommodation Slido : Accommodation over time Donders (1864) and Duane (1912) AOA declines with age AOA is drastically reduced@ 60years, but due to depth of field/focus, subjective AOA does not reach 0D It is assumed that any distance Rx is corrected when measuring subjective AOA Depth of (object ) field & depth of (image) focus https://www.cyberphysics.co.uk/topics/medical/Eye/Depth_of_field_and_focus.htm Blur circle increases Larger pupil diameter Longer axial length Increased focussing error Accommodation Amplitude of Accommodation (AOA) =The maximum amount of accommodation an individual can exert Measured in dioptres (D) Pupil constriction AOA can be measured subjectively (actual change in power plus subjective depth of focus) and objectively Measured using RAF rule – pull up/push down method How do we measure Amplitude (AoA)? (Pre-presbyopes) Amplitude of accommodation - Push-up/pull-down method (RAF rule/Mallet unit) Review OPT402 (most common test) notes - Minus lens technique Accommodative facility - Lens rock See OPT503 Accommodative lag - Dynamic retinoscopy (MEM/Modified Nott) - May be only form of assessment in young children AOA: real life Px cannot maintain max accomm. effort for very long Over-exertion causes asthenopia If AoA is reduced wrt normal limits, asthenopia may also occur when attempting near tasks. Rule of thumb: px can exert about 2/3 of their AoA  AOA – Clinical Significance H&S may reveal symptoms which indicate reduced AoA What are possible causes? (or uncorrected hyperopia): HA-normally frontal and associated with near work Latent hyperopia Difficulty changing or maintaining focus Medication (anti psycotics) Near blur Pathology: Uveitis, Adie’s pupil, MS, Chronic (Sometimes distance blur) fatigue etc. Struggling to read Trauma (head trauma, often unequal AoA) Asthenopia (eye strain) Down’s syndrome and cerebral palsy Stress Drug/alcohol misuse Cataract/lens damage History & symptoms is important Accommodative lag Measure with near retinoscopy (dynamic ret) Some lag is normal (0.50-0.75D) Larger amount of lag has been linked to myopic progression: Hyperopic defocus during near work→ increasing myopia (some debate) Associated with near esophoria in young myopes → myopic progression. Accommodative anomalies Often occur with BV issues Combined accommodative and convergence insufficiency is quite common (exercises/specs) Accommodative insufficiency/infacility/fatigue/spasm →exercises or plus lenses/multis AC/A ratio: measurement of changes in convergence (prism dioptres) induced by 1D of accommodation. If high: they converge “too much” when accommodating. Can mean full cyclo rx does not resolve near esotropia (may need bfs) May effect post-surgical orthoptic outcomes In px (esp child) with symptoms → cycloplegic refraction, specs and possible orthoptic referral Case scenario 1 For an emmetropic patient what level of accommodation is required for an object at 40cm? Case scenario 2 What is the far point for a myope with prescription of -6.00DS? Case scenario 3 For an uncorrected +3.00D hyperopic patient what level of accommodation is required for an object at 25cm? Case scenario 4 For an uncorrected -5.00D myope, what level of accommodation is required to see an object at 10cm? Case scenario 5 What is the far point for a -6.00DS myope with 8D of accommodation? Case scenario 6 For an uncorrected -5.00D myope, what level of accommodation is required to see an object at 10cm? Further reading Keirl (2007) Clinical Optics and Refraction – Chapter 12 pages 124- 131 (very good for theoretical and practical principles) Benjamin, W.J. (2006) Borish’s Clinical Refraction. 2nd edn. St Louis, Mo: Butterworth- Heinemann/Elsevier. Elliot, D.B. (2014) Clinical Procedures in Primary Eye Care. 4th edn. Philadelphia: Saunders/Elsevier. Grosvenor, T. (2007) Primary Care Optometry. 5th edn. St Louis, Mo: Butterworth- Heinemann/Elsevier. Rosenfield, M. & Logan, N. (2009) Optometry: Science, Techniques and Clinical Management. 2nd edn. London: Butterworth-Heinemann/Elsevier Tunnacliffe, A.H. (1993) An introduction to visual optics. 4th edn. Canterbury : Association of British Dispensing Opticians Rabbetts, R.B. (2007) Bennett and Rabbetts' Clinical visual optics. 4th edn. Edinburgh : Butterworth-Heinemann/Elsevier