Hyperopia

• Hypermetropia


  Refractive state of eye where parallel rays of light coming from infinity are focused behind the sentient layer of retina with accommodation being at rest

  
• Hyperopia


  Also called longsightedness
• Hypermetropia first suggested by KASTNER

  1755
• The posterior focal point is behind the retina which receives a blurred image

  
• Etiology of hypermetropia

  • Axial
  • Curvature
  • Index
  • Positional
  • Absence of lens

  
• Axial hypermetropia


  • Most common
  • Total refractive power of eye is normal
  • Axial shortening of eyeball
  • 1mm short- 3 D of HM
  • Physiologically more than 6D HM are uncommon
  • At birth +2.5 – 3 D of HM (physiologically)
  • Pathologically seen in cases like orbital tumour, inflammatory mass , oedema, coloboma and microphthalmos

  
• Curvature hypermetropia


  • Flattening of cornea, lens or both
  • 1mm increase in Radius of curvature- RESULTS IN 6D of HM
  • Never exceed 6D HM physiologically
  • Congenitally flattened (cornea plana)
  • Result (trauma and disease)
• Index hypermetropia


  • Change in refractive index with age
  • Physiologically in old age
  • Pathologically in diabetics under treatment
• Positional hypermetropia


  • Posteriorly placed crystalline lens
  • Occurs as congenital anomaly
  • Result of trauma or disease

  
• Absence of lens


  • Causes hypermetropia
• Clinical types of hypermetropia

  • Simple hyperopia
  • Pathological
  • Functional hyperopia
• Simple hyperopia


  • Most common form
  • Results from normal biological variations in the development of eyeball
  • Include axial and curvature HM
  • May be hereditary
• Pathological hypermetropia


  • Anomalies lie outside the limits of biological variation
  • Acquired hypermetropia - Decrease curvature of outer lens fibers in old age, Cortical sclerosis
  • Positional hypermetropia
  • Aphakia
  • Consecutive hypermetropia

  
• Functional hypermetropia


  • Results from paralysis of accommodation
  • Seen in patients with 3rd nerve paralysis & internal ophthalmoplegia
• Optical condition in hypermetropia

  • Parallel rays focus behind retina
  • Diffusion circles produce blurred & indistinct images
  • Retina is nearer to nodal point
  • Image is smaller than in emmetropic
  • Rays diverge from retina
  • Formation of clear image is possible only when converging power of eye is increased

  
• Components of total hypermetropia

  • Latent
  • Manifest (facultative + absolute)
• Total hypermetropia


  Total amount of refractive error, estimated after complete cycloplegia with atropine
• Latent hypermetropia


  • Corrected by inherent tone of ciliary muscle
  • Usually about 1D
  • High in children
  • Decreases with age
  • Revealed after abolishing tone of ciliary muscle with atropine
• Manifest hypermetropia


  • Remaining part of total hypermetropia
  • Correct by accommodation and convex lens
  • Measure by add strongest lens with max. vision
  • Consists of facultative & absolute

  
• Facultative hypermetropia


  Corrected by patients accommodative effort
• Absolute hypermetropia


  • Residual part. Not corrected by patients accommodative effort
  • Can be measured by the weakest convex lens with which maximum visual acuity

  
• Manifest hypermetropia - absolute hypermetropia = Facultative hypermetropia
• Total hypermetropia - Manifest hypermetropia = Latent hypermetropia

  
• Normal age variation in hypermetropia

  • At birth +2+3D HM
  • Slightly increase in one year of life
  • Gradually diminished until by the age 5-10 years
  • In old age after 40 year again tendency to HM - Tone of ciliary muscle decreases, Accommodative power decreases, Some amount of latent HM become manifest, More amount of facultative HM become absolute
  • Practically after 65 year all of it become absolute
• Symptoms of hypermetropia


  • Blurring of vision for close work
  • Asymptomatic - small error produces no symptoms, Corrected by accommodation of patient
  • Asthenopia - Refractive error are fully corrected by accommodative effort, Sustained accommodation produces symptoms like tiredness, frontal or fronto temporal headache, watering of the eyes, mild photophobia
  • Defective vision with asthenopia - Not corrected by accommodation, Defective vision for near more than distance, Asthenopia due to sustained accommodation, Refractive error more(>4D)
  • Defective vision only - Refractive vision more than 4D, Adults usually do not accommodate, Marked defective vision for near and distance

  
• Signs of hypermetropia


  • Defective visual acuity
  • Eyeball small or normal in size
  • Cornea may be smaller than normal, There can be cornea plana
  • Anterior chamber may be shallow
  • Lens could be dislocated backwards
  • A-Scan ultrasonography (biometry) reveal short axial length

  
• Complications of hypermetropia


  • Recurrent styes, blepharitis or chalazia
  • Accommodative convergent squint
  • Amblyopia - Anisometropic, Strabismic, Uncorrective bilateral high hypermetropia
  • Predisposed to develop primary narrow angle glaucomas
• Basis for treatment of hypermetropia

  • No Treatment - Error is small, Asymptomatic, Visual acuity normal, No muscular imbalance
  • Treatment required in young children (<6 or 7yrs) - if error is high or strabismus is present, when working in school small error may require correction, error tends normally to diminish with growth so refraction should be carried out every six months and if necessary, the correction should be reduced
  • In adults - If symptoms of eye-strain are marked, correct as much of the total hypermetropia as possible, When there is spasm of accommodation correct the whole of the error, Some patients with hypermetropia do not initially tolerate the full correction indicated by manifest refraction so undercorrect them, Exophoria hyperopia should be undercorrected by 1 to 2D, Patients with absolute hypermetropia are more likely to accept nearly the full correction, In pathological hypermetropia the underlying cause rather than the hypermetropia is chief concern
• Modes of treatment for hypermetropia

  • Spectacles
  • Contact lens
  • Surgical
• Spectacles for hypermetropia


  • Prescribe convex lenses(Plus lenses) so that rays are brought to focus on the retina
  • Comfortable, Easier method, Less expensive, Safe idea

  
• Contact lenses for hypermetropia

  Cosmetically good, Increased field of view, Less magnification, Elimination of aberrations & prismatic effect
• Refractive surgery for hypermetropia

  • Hexagonal keratotomy (HK) - Low to moderate degrees of hypermetropia, Risk/benefit ratio is not low enough to warrant its continued use
  • Laser thermal keratoplasty (LTK) - Procedure done using laser energy to heat the cornea (contraction of collagen) and increase its curvature
  • Photorefractive keratectomy (PRK) - Direct laser ablation of corneal stroma after removal of corneal epithelium mechanically
  • Laser assisted in situ keratomileusis (LASIK) - Anterior flap of cornea lifted with keratome and excimer laser is used to sculpt the stromal bed to change the refractive error of eye, Can correct up to 4D of hypermetropia and 8D of astigmatism
  • Phakic IOL and clear lens extraction - Done by Phaco technique, Clear lens extraction with the implantation of an IOL
• Visual hygiene for hypermetropia

  • Take a break about every 30 min while reading or doing intensive near work
  • Maintain proper distance when reading, the book should be at least as far from your eyes as your elbow
  • Sufficient Illumination
  • Place a limit spent watching television & watching videogames, Sit 5-6 feet away from the television
• Appropriate optical correction almost always leads to clear and comfortable single binocular vision

  
• Younger children who have significant hyperopia associated with amblyopia, strabismus,or anisometropia require treatment, starting as early as 3-6 months of age
• Hyperopia is a common refractive disorder that has been overshadowed by myopia in public perception,vision research & the scientific literature
• Although uncorrected myopia has a greater adverse effect on visual acuity than uncorrected hyperopia,the close association between hyperopia,amblyopia & strabismus,especially in children,makes hyperopia a greater risk factor for more permanent vision loss than myopia

  
• The early diagnosis & treatment of significant hyperopia & its consequences can prevent a significant amount of visual disability in the general population