Occupational Optometry and Display Screen Equipment (DSE) Notes

Occupational Terminology and Historical Context

• Visual Display Unit (VDU), Screen Based Equipment (SBE), and Display Screen Equipment (DSE) are synonymous terms for electronic displays.
• Early safety investigations focused on electromagnetic (EM) spectrum radiation, including ionizing (X-rays) and non-ionizing (microwaves) radiation.
• The Newspaper Guild of New York and the New York Times arbitration found no scientific link between computer use and cataracts, though health monitoring was mandated.

Defining Visual Comfort and Usage Demographics

• Computer Vision Syndrome (CVS) (coined by James Sheedy): Eye and vision problems related to near work during computer use.
• Digital Eye Strain (term promoted by Mark Rosenfield).
• Visual discomfort is often multifactorial, linked to external factors like stress, work pressure, and environmental conditions rather than just the visual system.
• 2018 UK Usage Data: 87% of adults use digital devices. Non-user proportions increase with age: $16\text{-}24$ ($1\%$), $65\text{-}74$ ($15\%$), and $75+$ ($48\%$).
• Non-use is highest in the DE socio-economic group ($23\%$).

SBE Symptomatology and Ocular Complaints

• Pain Classification: "Internal" (behind eyes, frontal headaches) or "External" (irritation, itching, tearing).
• VDU issues often arise from task demands (distance, angle, text size, duration) making underlying issues noticeable, rather than causing direct damage.
• Blinking Dynamics: Blinking frequency drops from $22$ per minute (relaxed) to $10$ (reading a book) and $7$ (reading a computer screen).
• Research by Rosenfield et al. identified "incomplete blinks" in screen users as a contributor to dry eye.
• Corneal exposure increases on desktops due to higher gaze angles.

Clinical Assessment and Binocular Vision

• Acuity Reserve: A $3:1$ ratio is recommended for comfort ($2:1$ minimum). Required targets include:
  • $3\,mm$ characters at $68.7\,cm$ (Desktop).
  • $2\,mm$ characters at $45.8\,cm$ (Laptop).
  • $1\,mm$ characters at $22.9\,cm$ (iPhone).
• Accommodative Facility: Symptomatic patients may manage only $2\text{-}3$ cycles per minute with $\pm 1.50\,DS$ or $\pm 2.00\,DS$ flippers, compared to $10+$ for asymptomatic patients. Management may involve $+0.75$ adds for pre-presbyopes.
• Phoria and Convergence: Use the Mallett unit at the specific DSE distance for fixation disparity. Near Point of Convergence (NPC) should be checked $3$ times.
• V-pattern exophoria: Coordination is poorer in up-gaze due to cyclo-rotation of the eyes.

Management Rules and Recommendations

• Ideal Monitor Position: $10^{\circ}$ downward gaze, at a distance of $60\text{-}70\,cm$, with eyes level with the screen top.
• 90-90-90 Posture Rule: Elbow, knee, and ankle joints at $90^{\circ}$ angles.
• The 20-20-20 Rule: Every $20$ minutes, look at something $20$ feet away for $20$ seconds.
• Lighting: Manage glare by repositioning lights or monitors; anti-reflection (MAR) coatings on lenses do successfully stop lens reflections but do not stop screen glare.

Legal Framework and Occupational Responsibilities

• Health and Safety (Display Screen Equipment) Regulations 1992 (SI 2792): Governs UK DSE eye care.
• Habitual User: Defined as anyone using DSE for more than $1\,hour$ per day.
• Employer Obligations: Employers must fund full eye exams for habitual users. They must pay for spectacles only if they are specific for VDU use (e.g., intermediate single vision).
• Screening: Can be in-house or by an optometrist, but a failure requires referral for a full eye examination.

Lens Selection and Blue Light Debate

• Enhanced Single Vision Lenses: Low reading additions for non-presbyopes (e.g., Zeiss Digital $+0.50D$ to $+1.25D$; Essilor Eyezen $+0.40D$ to $+0.85D$). There is little concrete clinical evidence for their benefit beyond subjective satisfaction.
• Blue Light Damage: Retinal damage from screens is physically impossible under regular use. Reaching safety thresholds requires staring at a smartphone for $234$ days straight or a computer for $314$ days straight ($24/7$).
• Circadian Rhythms: Peak sensitivity is at $470\text{-}480\,nm$. Melatonin suppression at the Suprachiasmatic Nucleus (SCN) requires brightness ($1000\text{-}2000\,lux$). Practitioners should recommend lowering brightness and increasing distance rather than tints.
• Regulatory Action: In 2015, the Advertising Standards Authority (ASA) banned a Boots Opticians advert for misleading claims about blue light damage.